bluuebunny/crossref_metadata_2025 huggingface dataset:
Slow recovery from inactivation of inward currents in mammalian myocardial fibres
Authors: Gettes L. S. , Reuter H.
Published: December 2014

1. Reactivation kinetics of the rapid and slow inward currents in ventricular fibres have been assessed by studying the maximum rate of rise ((dV/dt)max) of the action potential upstroke and the duration of the plateau in progressively earlier premature responses. Reactivation of the slow inward current was also studied by voltage clamp technique in sheep and pig ventricular trabeculae.

2. The time constant of recovery of (dV/dt)max was voltage dependent and increased from less than 20 msec when the resting membrane potential was more negative than −80 mV to more than 100 msec when the resting membrane potential was between −65 and −60 mV. Similar results were obtained in Purkinje fibres. These results suggest that the time constant for reactivation is slower than the time constant for inactivation of the rapid inward current system by at least one order of magnitude.

3. The time constant of recovery of plateau duration was also voltage dependent and increased from 30 to 70 msec as the membrane potential was changed from −85 to −60 mV.

4. The reactivation time constant of the slow inward current determined by voltage clamp experiments were similar to the results obtained by analysis of plateau duration. At potentials less negative than −60 mV the time constant of reactivation became progressively longer. Unlike reactivation time constants of (dV/dt)max, the time constants of reactivation of the slow inward current were similar to the time constants of inactivation.

5. Our results indicate that (a) in premature action potentials, time as well as voltage are important determinants of (dV/dt)max in myocardial and Purkinje fibres, (b) the kinetics of reactivation of the rapid inward current in cardiac fibres are different from those in nerve and (c) plateau duration of premature action potentials in ventricular myocardial fibres is largely determined by the kinetics of reactivation of the slow calcium inward current.
Differential reaction of fast and slow α‐motoneurones to axotomy
Authors: Kuno M. , Miyata Y. , Muñoz‐Martinez E. J.
Published: December 2014

1. The properties of medial gastrocnemius (m.g., fast α) and soleus (sol., slow α) motoneurones of the cat were examined with intracellular electrodes 8–119 days after section of the muscle nerves.

2. The axonal conduction velocity was significantly decreased in both m.g. and sol. motoneurones after chronic section of the muscle nerves.

3. The amplitude of overshoot of action potentials was significantly increased in both m.g. and sol. motoneurones following section of the muscle nerves.

4. No significant changes in the resting membrane potential or the input resistance were observed for sol. motoneurones, whereas m.g. motoneurones showed a slight decrease in the resting potential and a slight increase in the input resistance.

5. The duration of after‐hyperpolarization was significantly decreased in sol. motoneurones, whereas that in m.g. motoneurones remained virtually unchanged or increased slightly following section of the muscle nerves.

6. The changes described above were not seen in the preparations examined 29–46 days after section of the lumbosacral dorsal roots, suggesting that alterations in the motoneurone properties observed after section of the muscle nerves resulted from axotomy of the motoneurones rather than from sensory deprivation.

7. The differences in electrophysiological properties between m.g. and sol. motoneurones were less prominent in axotomized animals than in control, unoperated cats.

8. It is concluded that fast (m.g.) and slow (sol.) α‐motoneurones have qualitatively different properties. A possible ‘dedifferentiation’ of fast and slow α‐motoneurones by axotomy is discussed.
The permeability to tetraethylammonium ions of the surface membrane and the intercalated disks of sheep and calf myocardium
Authors: Weingart Robert
Published: December 2014

1. Efflux experiments and longitudinal diffusion experiments were performed to determine the permeability of the surface membrane and of the nexal membrane of sheep and calf ventricular muscle to radioactive [1‐14C]tetraethylammonium cations ([14C]TEA) at 25° C.

2. Efflux curves were analysed as the sum of three exponential processes with time constants for TEA loss of 2·7, 13·3, and 832 min.

3. The first component was attributed to the exchange of extracellular free TEA, the second to extracellular, probably mucopolysaccharide bound TEA, and the third to intracellular free TEA.

4. From the decay of the first phase the tortuosity factor for extracellular radial movement of TEA ions was calculated as 1·59.

5. The permeability of the surface membrane to [14C]TEA was estimated as 6·06 × 10−8 cm/sec.

6. A tenfold change of [K]o from 5·4 to 54 m
M resulted in a 2·75‐fold decrease of the permeability of the surface membrane; a fifteenfold change (5·4 to 81 m
M) resulted in a 4·24‐fold decrease.

7. From longitudinal non‐steady state diffusion experiments the permeability of the nexal membrane to [14C]TEA turned out to be 1·27 × 10−3 cm/sec.

8. The permeability of the nexal membrane to TEA is 21,000 times larger than that of the surface membrane. This finding is consistent with the concept of low resistance pathways between myocardial cells.

9. From a comparison of the dimensions of radiopotassium, [14C]TEA and Procion Yellow, and the study of their diffusional properties, the pores within the nexal membrane of the intercalated disks are deduced to have a diameter of somewhat more than 10 Å.
Selective glycogen depletion pattern in human muscle fibres after exercise of varying intensity and at varying pedalling rates
Authors: Gollnick P. D. , Piehl Karin , Saltin B.
Published: December 2014

1. Glycogen depletion pattern in human skeletal muscle fibres was studied after bicycle exercise of varying intensity performed at different pedalling rates. Work intensities studied were equivalent to 30–150% of V̇O2 max. with pedalling rates of 30–120 rev/min.

2. Glycogen depletion increased dramatically with increasing exercise intensity; depletion was 2·7 and 7·4 times greater respectively at workloads demanding 64 and 84% V̇O2 max. than at workloads calling for 31% V̇O2 max. Even greater rates of glycogen utilization occurred at supramaximal loads.

3. Slow twitch, high oxidative (ST) fibres were the first to lose glycogen (reduced PAS staining) at all workloads below V̇O2 max. Progressive glycogen depletion occurred in fast twitch (FT) fibres as work continued. Large quantities of glycogen remained in the muscle after 3 hr of exercise at low exercise intensity. This was almost exclusively found in FT fibres. At workloads exceeding maximal aerobic power, there was an initial depletion of glycogen in both fibre types. Varying the pedalling rate and, thus, the total force exerted in each pedal thrust had no effect on the pattern of glycogen depletion in the fibres.

4. Results point to primary reliance upon ST fibres during submaximal endurance exercise, FT fibres being recruited after ST fibres are depleted of glycogen. During exertion requiring energy expenditure greater than the maximal aerobic power, both fibre types appeared to be continuously involved in carrying out the exercise.
Absence of action potentials in frog slow muscle fibres paralysed by botulinum toxin
Authors: Miledi R. , Spitzer N. C.
Published: December 2014

1. As shown previously, slow muscle fibres of the frog develop the ability to produce action potentials in 2 weeks after denervation.

2. Normal transmission at the slow fibre neuromuscular junction gives a junction potential of 11 mV average (range 6–20 mV), caused by summation of potentials from several motor axons.

3. Botulinum toxin injected intramuscularly into the iliofibularis blocks the neuromuscular junction of slow fibres in 6 days at room temperature. Single nerve stimuli give junction potentials of 0·05 mV average (range 0–1·6 mV). Contraction of slow fibres in response to tetanic stimulation is eliminated.

4. No action potentials could be elicited in botulinum treated fibres, even 6½ weeks after injection of toxin. This finding is discussed in relation to the possible involvement of a ‘trophic’ factor regulating the action potential mechanism in frog slow muscle fibres.
The absorption of a mixture of amino acids by rat small intestine
Authors: Bronk J. R. , Leese H. J.
Published: December 2014

1. The absorption of a mixture of amino acids by the small intestine has been studied in vitro with mucosal slices from rat jejunum. The mixture contained eighteen amino acids and was used at a concentration of 9·5 m
M in the incubation medium. The uptake of fifteen of the amino acids was followed in each sample with the aid of an amino acid analyser.

2. The endogenous amino acid content of the slices decreased during preparation and further substantial losses occurred when the slices were preincubated for 30 sec before the addition of the amino acid mixture to the incubation medium.

3. When the slices were incubated with the amino acid mixture for 4·5 min all of the amino acid studied were accumulated to give concentration ratios of approximately 2·0.

4. The amino acids were taken up rapidly by the tissue so that on average 82% of the amino acids absorbed in 4·5 min had already accumulated after one min of incubation.

5. The data for individual amino acids revealed no obvious competition between the various amino acids, and the extent to which the various amino acids were accumulated by the tissue was proportional to their concentrations in the mixture.

6. When the Na+ in the incubation medium was replaced by Li+, the slices accumulated all of the amino acids studied to concentrations significantly higher than those in the incubation medium. However, the concentration ratios obtained with the Li+ medium were all lower than those obtained with the Na+ medium and averaged slightly more than 1·5.

7. When the Na+ in the incubation medium was replaced by K+ there was little amino acid accumulation, although concentration ratios significantly greater than one were achieved for aspartic acid, glycine, histidine and methionine.
Indomethacin and the prostaglandin hypothesis of coronary blood flow regulation
Authors: Afonso Skoda , Bandow George T. , Rowe George G.
Published: December 2014

1. Recent experimental data support the view that prostaglandins might be involved in autoregulation of coronary blood flow. Since indomethacin blocks prostaglandin synthesis, the present study was performed to determine whether indomethacin also inhibits coronary vasodilatation induced by hypoxia.

2. Coronary and systemic haemodynamic and metabolic effects of hypoxia (5% and 8% oxygen in nitrogen) were studied in intact, anaesthetized and vagotomized dogs before and after indomethacin.

3. 30 and 60 min after administration of indomethacin coronary blood flow increases produced by hypoxia were considerably lower than those before indomethacin.

4. These results are held to lend support to the hypothesis that prostaglandins are involved in the autoregulation of coronary blood flow.
Stimulation of the hypothalamus and ovulation in the guinea‐pig
Authors: Booth Janet E. , Donovan B. T.
Published: December 2014

1. Various methods of stimulating the hypothalamus were applied to the guinea‐pig with the aim of inducing ovulation.

2. Electrochemical stimulation of the hypothalamus, or gross stimulation of the brain, was ineffective.

3. Electrical stimulation of the medial basal hypothalamus or rostral hypothalamus elicited gonadotrophin release.

4. Despite variation of the time and intensity of stimulation, follicular luteinization was more common than the formation of new corpora lutea.

5. Electrical stimulation of the medial basal hypothalamus often caused luteinization of follicles. Fewer animals responded to excitation of the rostral hypothalamus, but in those that did, ovulation occurred more frequently.

6. The present observations contrast markedly with comparable studies on the rat, where both electrochemical and electrical stimulation of the hypothalamus readily induce ovulation.
Histamine metabolism of the gastric mucosa following antrectomy
Authors: Lundell L.
Published: December 2014

1. Histamine metabolism of the gastric mucosa in rats subjected to antrectomy, antrectomy and substitution with pentagastrin and exclusion of the antrum has been investigated employing various in vivo and in vitro methods.

2. Mucosal histamine formation after antrectomy fell to about one third, whereas after antrum exclusion histamine formation increased many‐fold.

3. After antrectomy, mucosal histamine content decreased, and increased after antrum exclusion.

4. After total gastrectomy, (a) whole‐body histamine formation was reduced to about half, as judged by determining histamine excretion, and (b) pentagastrin infusion did not increase histamine excretion, showing absence of histamine mobilization from extra‐gastric sources. In rats with the stomach retained, infusion of pentagastrin induced a dose‐dependent increase in histamine excretion.

5. Kinetic studies in which [14C]histidine was injected and the resulting urinary [14C]histamine determined showed that on pentagastrin infusion after antrectomy newly formed histamine was initially mobilized to a larger extent than in the controls.

6. Antrectomized rats were subjected to substitution treatment by three injections per day of pentagastrin. After 3 weeks of substitution, histamine excretion was considerably higher than without substitution. After 6 weeks of substitution, histamine excretion was about the same in the substituted antrectomized, non‐substituted antrectomized and sham‐operated groups. Neither time nor substitution could, however, normalize the excretion of histamine on pentagastrin stimulation after antrectomy.

7. In non‐substituted antrectomized rats, pentagastrin was less effective in elevating mucosal histamine formation than in the substituted and sham‐operated groups.

8. The indispensability of the rat in this kind of study is emphasized.
Intracellular sodium and potassium concentrations in toad and frog oocytes during development
Authors: Cannon J. D. , Dick D. A. T. , Ho‐Yen D. O.
Published: December 2014

1. During growth of oocytes of Bufo bufo from approximately 700–2000 μm in diameter, intracellular Na rose from 20 to 120 m‐mole/l. cell water while K fell from 120 to 15 m‐mole/l. cell water.

2. In Rana temporaria Na similarly rose from 9 to 190 m‐mole/l. cell water and K fell from 126 to 28 m‐mole/l. cell water.

3. At the same time in both Bufo and Rana the ouabain‐sensitive Na efflux, the ouabain‐insensitive Na efflux, and the total Na influx all increased.

4. It is concluded that the predominant process is an increase of passive Na permeability. The increase of apparently active Na efflux may be secondary to the consequent rise in intracellular Na.
The dispersion of solutes during blood flow through a straight tube
Authors: Lane D. A. , Sirs J. A.
Published: December 2014

1. The dispersion of solutes in plasma and blood has been studied by observing the clearance at a point down‐stream of a bolus of labelled solution by the steady flow of unlabelled solution.

2. With a low molecular weight solute the clearance curve is qualitatively similar in 2
N‐KCl solution, plasma and whole blood.

3. The dispersion of a high molecular weight protein, [131I]HSA, in plasma is dominated by the velocity profile of the flow.

4. The clearance curves for HSA in whole blood are similar to those of plasma, except that the red blood cells speed the clearance of protein in the tail region of the curve.

5. An analysis of the data suggests that the dispersion of solutes during blood flow through a straight tube can be attributed to the combined effects of solute diffusion and laminar convection. There is no evidence that induced motion of the erythrocytes produces significant mixing, in the bulk of the flow.
Synaptic transmission and cell death during normal ganglionic development
Authors: Landmesser Lynn , Pilar G.
Published: December 2014

1. During normal embryonic development of the chick ciliary ganglion, cell death over a 4‐day period (Stages 35–39) reduces the number of ganglion cells by half, from 6500 to 3200. Both ciliary and choroid populations are affected by approximately the same amount.

2. Previous to cell death, preganglionic fibres form functional synapses on all ganglion cells, indicating that synapses form on cells which are destined to die.

3. Shortly before the period of cell death, there is a failure of transmission in approximately half the cells. Some evidence suggests that transmission failure in at least some of the cells is of preganglionic origin.

4. Cell death is nearly synchronous with the establishment of peripheral connexions by ganglion cells, at least with respect to the ciliary population which forms functional synapses with iris muscle. This implies that those cells which die do so because they have failed to form adequate peripheral connexions.

5. It is suggested that many of the cells in which transmission has failed die, bringing transmission through the ganglion back to 100%. However, transmission failure appears to be a transitory phenomenon in other cells which survive and probably results from death of their preganglionic elements. Restoration of transmission would then be brought about by the formation of new or more effective synapses by surviving preganglionic fibres.
The absorption of 125I‐labelled immunoglobulin G by different regions of the gut in young rats
Authors: Morris B. , Morris R.
Published: December 2014

1. 125I‐labelled homologous IgG was injected into different regions of the small intestine of rats aged 12, 16, 18, 20 and 22 days. At 12 days the proximal and middle regions of the intestine readily absorbed globulin and transmitted it to the circulation. The distal region of the intestine transmitted little to the circulation at all ages tested.

2. The intestine loses its ability to transmit globulin to the circulation in a distal‐proximal direction. At 16 and 18 days the ability of the middle region had declined significantly, and this decline continued so that little globulin was transmitted from this region at 20 and 22 days.

3. The proximal intestine retained the ability to transmit globulin to the circulation in significant amounts up to 20 days.

4. There is a close negative correlation between body weight and total radioactivity of the sera of rats which had received doses of labelled globulin into the proximal and middle regions of the intestine. There was no such correlation after injection into the distal intestine — suggesting a restricted throughput of radioactive material by the absorptive cells of this region.

5. These results are discussed in the context of the termination of antibody absorption, and in relation to the results obtained using polyvinyl pyrrolidone.
Evidence for the genetic control of the sodium pump density in HeLa cells
Authors: Boardman Lesley , Huett Marian , Lamb J. F. , Newton J. P. , Polson Jean M.
Published: December 2014

1. HeLa cells were grown in normal and altered growth solutions; the ion contents, volumes, K sensitive ouabain binding, the Na‐K‐ATPase and the Na and K transport measured.

2. Cells grown in 1 × 10−4
M ethacrynate or low‐K media for 24 hr have a raised [Na]i, a decreased [K]i, and an increased ouabain binding. Those grown in low‐K also have an increased Na‐K‐ATPase activity.

3. When cells are put into low‐K solutions the [Na]i initially rises to a high value, and then starts to fall some 8 hours later as the ouabain binding increases, suggesting that these additional sites represent working Na pumps. Flux measurements on low‐K cells provide some support for this view.

4. Experiments in which sorbitol replaced [Na]o showed that the increased ouabain binding and Na‐K‐ATPase was related to the increase in [Na]i rather than the decrease in [K]i and was not due to a non‐specific effect of [K]o change.

5. The protein synthesis inhibitors cycloheximide and puromycin stopped the effect of ethacrynate and low‐K solutions on increased ouabain binding. They also decreased the ouabain binding and K influx in normal cells over 24 hr. Cycloheximide had similar effects on Na‐K‐ATPase in low‐K treated and normal cells. These results suggest that protein synthesis is required for the appearance of more ouabain sensitive sites in the cell membrane, both in response to ethacrynate and low‐K treatment and for normal replacement during the cell's life.

6. The RNA synthesis inhibitors actinomycin D (AMD) and cordycepin had complex effects on ouabain binding in fresh and ethacrynate treated cells. These inhibitors increased the ouabain binding but decreased the K influx. This discrepancy was due to the appearance of ouabain binding sites with different characteristics from normal sites. A limited investigation of this phenomenon was carried out. Probably AMD stops the normal replacement of sites in the membrane.

7. These results are consistent with the hypothesis that HeLa cells have a system for controlling the number of Na pumps in their membranes. This system responds to the level of [Na]i within the cell and involves protein synthesis. It is not clear to what extent the nucleus is normally involved in this process.
Steady‐state contribution of the sodium pump to the resting potential of a molluscan neurone
Authors: Gorman A. L. F. , Marmor M. F.
Published: December 2014

1. The electrogenic contribution of the Na+‐K+ exchange pump to the membrane potential of the Anisodoris giant neurone (G cell) was examined under steady‐state and Na+ loaded conditions.

2. The membrane potential was variable for the first 1‐4 hr after impalement, but, in the absence of experimental manipulation, remained constant thereafter. The average membrane potential for ten cells maintained at 11–13 °C and measured 5‐36 hr after impalement was 55·8 ± 1·0 mV (
S.E. of mean).

3. Low concentrations of external ACh caused a reversible increase in membrane Na+ conductance. Brief exposure to ACh proved a fast and reversible technique to load the cell with Na+ ions, and transiently stimulate the electrogenic Na+ pump.

4. In ten cells maintained from 5 to 36 hr at 11–13° C the reduction in membrane potential produced by inhibition of the Na+ pump with ouabain was remarkably constant between cells and averaged + 9·7 mV.

5. Cells maintained under steady‐state conditions (at 11–13° C) for extended periods of time were shown to be relatively insensitive to changes in temperature and to small changes in external K+.

6. It is estimated that the Na+‐K+ exchange pump contributes approximately ‐ 10 mV to the steady‐state resting potential of the G cell, and that two Na+ ions are extruded for every K+ ion transported into the cell per pump cycle.
Membrane potential and resistance measurement in acinar cells from salivary glands in vitro: effect of acetylcholine
Authors: Nishiyama A. , Petersen O. H.
Published: December 2014

1. Cell membrane potential and input resistance measurements were made on segments of submaxillary glands from mice, rabbits or cats placed in a tissue bath, which was perfused with physiological salt solutions.

2. During exposure to a standard Krebs—Henseleit solution, ACh stimulation always evoked a marked decrease in input resistance and time constant. The change in potential evoked by ACh stimulation was either a monophasic hyperpolarization (low resting potential) or a depolarization followed by hyperpolarization (high resting potential).

3. Increasing [Ca]o from 2·56 to 10 m
M resulted in an enhanced input resistance. Under this condition it was sometimes possible to obtain current—voltage relations. The relationship was linear in the range −50 to −10 mV. In the absence of extracellular Ca the resting potential was reduced and ACh mostly evoked hyperpolarizations. In those cases when the resting potential remained high biphasic potentials were still observed.

4. During exposure to Na‐free solutions the resting potential was either unchanged or slightly enhanced. ACh never evoked biphasic potentials, but always large hyperpolarizations.

5. In the first period (1 hr) after exposure to a K‐free solution ACh normally evoked very large hyperpolarizations, often to more than −100 mV. After several hours of exposure to K‐free solution the input resistance gradually increased and ACh evoked a tremendous fall in input resistance and time constant with only a small potential change. Re‐introducing control solution, ([K]o = 4·7) for a short period at this stage, caused a very marked hyperpolarization (about 30 mV) unaccompanied by a change in input resistance and time constant.

6. Replacing extracellular Cl by SO4 hyperpolarized the cell membrane. ACh mostly evoked hyperpolarization under this condition, but occasionally biphasic potentials were observed. Increasing [K] of the sulphate solution depolarized the cell membrane by about 49 mV per tenfold increase in [K]. In the presence of ACh the membrane behaved as a K‐selective membrane with a slope of the linear curve relating membrane potential to [K]o of 59 mV per tenfold increase in [K]o.

7. It is concluded that ACh evokes a marked increase in surface cell membrane permeability of salivary acinar cells. The ACh evoked hyperpolarization is due to an increase in PK: the depolarization frequently preceding the hyperpolarization is probably mainly related to an increase in PNa. The membrane Na—K pump can act electrogenically at least under conditions of Na loading.
The bleaching and regeneration of rhodopsin in the cat
Authors: Bonds A. B. , MacLeod Donald I. A.
Published: December 2014

1. The processes of bleaching and regeneration were monitored by retinal densitometry in living cats.

2. Neither bleaching nor regeneration of rhodopsin can be described by the simple kinetic equation (Alpern, 1971) found valid for man.

3. After a strong 1 min bleach, the retina contains more unbleached rhodopsin than expected on the basis of the initial bleaching rate.

4. During the first 9 min after a 1 min bleach, cats regenerate rhodopsin only slowly; density changes during this period are dominated by formation and decay of metarhodopsin III. Subsequently, rhodopsin regeneration accelerates to a rate of 50%/11 min.

5. No such delay precedes recovery from a prolonged (20 min) bleach.
Mechanism of nerve membrane depolarization caused by grayanotoxin I
Authors: Narahashi Toshio , Seyama Issei
Published: December 2014

1. The mechanism of depolarization of squid axon membranes caused by grayanotoxin I has been studied by means of internal perfusion and voltage clamp techniques.

2. The depolarization induced by either internal or external application of grayanotoxin I was reversed by decreasing the external sodium concentration from 449 to 1 m
m.

3. No depolarization was observed when both external and internal media were devoid of sodium ions, indicating that the depolarization by grayanotoxin I in normal media is due to a specific increase in resting sodium permeability.

4. The resting sodium permeability as measured by voltage clamp was increased to 1·31 × 10−6 cm/sec by internal application of 1 × 10−5
m grayanotoxin I, an increase by a factor of about 90.

5. The apparent dissociation constant of internally applied grayanotoxin I in increasing the resting sodium permeability was estimated to be 4·12 × 10−5
m, and the toxin interacts with the membrane receptor on a one‐to‐one stoichiometric basis.

6. Tetrodotoxin antagonized the action of grayanotoxin I in increasing the resting sodium permeability in a non‐competitive manner.
Effects of acetylcholine and carbamylcholine on the axon and Schwann cell electrical potentials in the squid nerve fibre
Authors: Villegas Jorge
Published: December 2014

1. The effect of acetylcholine and carbamylcholine on the axon and Schwann cell membrane potential have been studied in the giant nerve fibre of the squid. The addition of carbamylcholine (10−6
M) to the external sea‐water medium has no appreciable effects on the resting and action potentials of the axon. However, it induces a long‐lasting hyperpolarization in the surrounding Schwann cells of the unstimulated intact or slit nerve fibres which is completely blocked by
D‐tubocurarine (10−9
M). Eserine (10−9
M) prolongs the Schwann cell hyperpolarizations induced by a 1 min exposure of the unstimulated nerve fibres to acetylcholine (10−7
M).

2. The addition of carbamylcholine (10−6
M) to the external medium increases the relative permeability of the Schwann cell membrane to the potassium ion in slit nerve fibres. Yet, a hundredfold reduction in external sodium concentration has no appreciable effect on the hyperpolarization of the Schwann cells of the slit nerve fibre under similar conditions.

3. Tetrodotoxin at a concentration of 5 × 10−8
M has no appreciable effects on either the Schwann cell electrical potential or on the hyperpolarizing action of carbamylcholine on the Schwann cells of the unstimulated intact nerve fibres.

4. These findings indicate the presence of acetylcholine receptors in the plasma membrane of the Schwann cell in these nerve fibres and give further support to the hypothesis on the role of the cholinergic system in the genesis of the long‐lasting Schwann cell hyperpolarizations caused by the conduction of nerve impulse trains by the axon.
Changes in colostrum composition and in the permeability of the mammary epithelium at about the time of parturition in the goat
Authors: Linzell J. L. , Peaker M.
Published: December 2014

1. Changes in milk composition and in mammary permeability to labelled sucrose and monovalent ions have been studied in late pregnancy and at the time of parturition. These data have been compared with those obtained previously in lactating goats.

2. Colostrum contained more sodium, chloride, protein, immunoglobulins and less potassium and lactose than milk. The composition of the aqueous phase changed near term and normal milk composition was reached either several days before or several days after parturition. The main decrease in the immunoglobulin concentration occurred when the animal was first milked or suckled.

3. In contrast to lactating animals, [14C]sucrose passed from blood to milk and [14C]lactose from milk to blood. There was a significant correlation between the entry of labelled sucrose into milk and the sodium concentration.

4. The rate of passage of 24Na and 36Cl into milk from blood was higher in late pregnancy than in lactation.

5. In late pregnancy, the concentrations of both sodium and chloride were inversely correlated with the concentration of lactose while there was a positive correlation between potassium and lactose.

6. Hydrostatic pressure in the lumen of the mammary gland increased during late pregnancy but there was no significant correlation with the composition of the aqueous phase of milk.

7. When one gland of 4 animals was milked twice‐daily starting 9–19 days before parturition, the composition of the secretion changed to that of normal milk only in the gland that was being milked. Similarly, [14C]sucrose, 24Na and 36Cl entry from blood decreased. Milk yield also increased but a further increase occurred post‐partum.

8. Comparison of the passage of 3HOH, 24Na and 36Cl into different fractions of milk during
I.A. infusions indicates that the mammary ducts are less permeable to ions than the alveoli, but it was not possible to decide whether the ducts are as impermeable as during lactation.

9. It is suggested that ion and lactose movements occur via a para‐cellular route and these results are discussed in relation to transport mechanisms and in terms of local and systemic controlling mechanisms.
Ionic relations and electrical properties of isolated oocytes of Bufo bufo with special reference to removal of extracellular chloride
Authors: Hannibal O. H. , Lea E. J. A.
Published: December 2014

1. The efflux rate coefficients of sodium, potassium and chloride from immature oocytes of the toad Bufo bufo have been measured and found to be respectively, 0·0069, 0·0023 and 0·0034 min−1.

2. Replacement of external chloride by sulphate resulted in a fall in chloride efflux of about 50%. This has been interpreted in terms of exchange diffusion.

3. The membrane conductance has been measured and found to be 0·14 × 10−3 mhos cm−2 in good agreement with the value calculated from the flux data, 0·12 × 10−3 mhos cm−2, after taking account of the chloride exchange diffusion fraction.
Periodic components in steady‐state activity of cuneate neurones and their possible role in sensory coding
Authors: Amassian Vahé E. , Giblin Denis
Published: December 2014

1. Individual cuneate touch, touch‐hair and proprioceptive neurones often display periodic components in their steady‐state resting or evoked discharges. The periods may be visible in the interspike interval distribution or may be revealed only by the expectation density function. Several levels of complexity were identified; from one to four mutually prime, periodic components may be present, with or without an aperiodic component.

2. The periodic components usually depend on the peripheral input, as shown by their introduction or modification by peripheral stimulation and by their disappearance following deafferentation.

3. The coefficient of variation of periodic discharges by touch and touch‐hair neurones was 0·024‐0·23 (aperiodic, driven discharges usually had CV's of 0·64‐0·77).

4. The occasional recording extracellularly of a periodically occurring, unitary prepotential preceding the spike and the intracellular recording of a periodic, ‘giant’, unitary e.p.s.p. imply that an individual periodic impulse in an afferent fibre may elicit a post‐synaptic discharge. Even with threshold stimulation, the timing of post‐synaptic discharge was quite precise.

5. The periodicity did not appear to reflect a cycle of subnormality intrinsic to the post‐synaptic neurone, because a current pulse injected through a micro‐electrode lying just external to the membrane could block the next expected periodic discharge, but did not continuously vary its waiting time.

6. A mathematical model that fits some discharge patterns predicts the interval distribution from an over‐all probability of response to the periodic input: each periodic afferent impulse is treated as an independent trial resulting in success (post‐synaptic discharge) or failure. Some other interval distributions are fitted by a ‘conditioned’ model in which a success reduces the probability of response at the next periodic trial.

7. The discussion includes a hypothesis of tactile discrimination, in which the output of a sensory relay, e.g. cuneate neurone, signals both the number of afferent fibres converging upon it and the afferent period in each.
Factors influencing plasma renin and angiotensin II in the conscious pregnant ewe and its foetus
Authors: Pipkin Fiona Broughton , Lumbers Eugenie R. , Mott Joan C.
Published: December 2014

1. Plasma renin (measured in the presence of additional substrate) was significantly higher (10·7 ± 1·1
S.E. of mean ng/ml.hr) in foetal lambs of 111–144 days gestation age (full term 147 days) than in their mothers (1·5 ± 0·2 ng/ml.hr
S.E. of mean, P < 0·001) but plasma angiotensin II concentrations were in the same range (ewe 47·3 ± 6·6
S.E. of mean, foetus 47·4 ± 14·1
S.E. of mean pg/ml.). The endogenous velocity of renin production by foetal plasma was also greater than that of maternal plasma.

2. Foetal plasma [Na+] (137 ± 0·8
S.E. of mean m‐equiv/l.), was lower than that in the ewe (142 ± 1·5 m‐equiv/l.
S.E. of mean, P < 0·01).

3. Foetal plasma renin in lambs of less than 120 days gestation was lower (9·2 ± 2·7
S.E. of mean ng/ml.hr) than that in lambs of over 130 days gestation (12·6 ± 2·6 ng/ml.hr
S.E. of mean, P < 0·01). Foetal plasma [K+] (3·8 ± 0·1
S.E. of mean m‐equiv/l.) was also lower in lambs of less than 120 days gestation than in those over 130 days (4·1 ± 0·1
S.E. of mean m‐equiv/l., P < 0·001).

4. When small volumes of blood (≤ 3% of blood volume) were withdrawn from foetal lambs, plasma renin increased. The% increase of plasma renin in hypoxaemic foetal lambs was significantly less (P < 0·05) than in control lambs. At the end of 60 min hypoxaemia, arterial pressure and plasma [K+] were significantly higher in hypoxaemic than in control foetal lambs.

5. During foetal hypoxaemia, plasma angiotensin II concentration increased concurrently with plasma renin.

6. Bilateral nephrectomy was performed in two foetal lambs. Plasma renin fell to very low levels and angiotensin II became undetectable.

7. Adrenaline (∼.0·42 μg/min.kg
I.V.) infused into the foetus did not alter foetal plasma renin. When adrenaline was infused into the ewe (∼0·26 μg/min.kg) maternal plasma renin increased. Maternal infusion of adrenaline raised foetal plasma renin significantly more (P < 0·05) than foetal infusion.

8. It is concluded that the foetal kidney is the major source of foetal renin in the last quarter of gestation and that renin release is stimulated by very small reductions of blood volume. Hypoxaemia does not augment renin release and cannot be responsible for high levels of renin and angiotensin associated with vaginal delivery.
Linear analysis of membrane conductance and capacitance in cardiac Purkinje fibres
Authors: Hellam D. C. , Studt J. W.
Published: December 2014

1. The membrane capacitance and slope conductance of sheep cardiac Purkinje tissue were examined under conditions of constant and slowly changing voltage within the potential range: −70 to −100 mV. Data were secured by applying constant current pulses, or by imposing ramp commands or small changes in holding potential under voltage clamp control.

2. The electrical measurements, combined with light and electron microscopic data on preparation structure, were interpreted with the aid of a core‐conductor model that permits quantitative representation of cleft‐ and lateral surface membranes for individual preparations (Hellam & Studt, 1974).

3. The analysis led to the following conclusions. The slope conductance of unit membrane area (Gm) is quite low in the normal resting potential range; at −80 mV the value is 0·09 mmho/cm2. Gm exhibits a marked decline with depolarization in the region positive to −88 mV, but only slight voltage‐dependence at more negative potentials within the range of present observations. The capacitance of unit membrane area (Cm), from voltage ramp data collected near −90 mV, is 0·9 μF/cm2.

4. Comparison with results of earlier studies indicates that the differences between present and previous experimental estimates of these membrane characteristics result from differences in modelling and structural analysis of tissue preparations.
Developmental changes of membrane electrical properties in a rat skeletal muscle cell line.
Authors: Kidokoro Y
Published: December 2014

1. The developmental changes of the cell membrane electrical properties were studied with micro‐electrodes in a rat skeletal muscle cell line. 2. The resting potentials in myoblasts were minus 71 plus or minus 3 mV (mean plus or minus S.D.) and those in myotubes which were formed by fusion of myoblasts were minus 69 plus or minus 3 mV. There was no developmental change in the resting potential during the period examined. 3. The ionic mechanism for the resting potential was the same in myoblasts and myotubes. The resting membrane was almost exclusively permeable to K ions, while permeability to Na ions was not detectable. There was a small permeability to Cl ions. 4. The specific membrane resistance and capacitance were 8 k omega. cm‐2 and 1 muF/cm‐2 for myoblasts and 12 k omege. cm‐2 and 5 muF/cm‐2 for myotubes, respectively. 5. Action potentials in myoblasts were evoked by anode break stimulation. They were small and did not overshoot zero membrane potential. The action potentials in myotubes were larger, and had an average overshoot of 32 plus or minus 7 mV and a maximum rate of rise of 93 plus or minus 28 V/sec. 6. The current‐voltage relation was examined. Delayed rectification was found in myotubes but not in myoblasts.
Natural convection around the human head.
Authors: Clark R P , Toy N
Published: December 2014

1. Factors determining the convective flow patterns around the human head in ‘still’ conditions are discussed in relation to body posture. 2. The flow patterns have been visualized using a schlieren optical system which reveals that the head has a thicker ‘insulating’ layer of convecting air in the erect posture than in the supine position. 3. Local convective and radiative heat transfer measurements from the head have been using surface calorimeters. These results are seen to be closely related to the thickness of the convective boundary layer flows. 4. The total convective and radiative heat loss from the head of a subject in the erect and supine position has been evaluated from the local measurements. For the head of the supine subject the heat loss was found to be 30% more than when the subject was standing.
Studies on the mechanism of fibrillation potentials in denervated muscle.
Authors: Thesleff S , Ward M R
Published: December 2014

1. Intracellular electrodes were used to study the origin of fibrillation potentials in chronically denervated rat muscle. 2. Fibrillation potentials were observed to start from spontaneous biphasic membrane potential oscillations. Each action potential was followed by an after‐hyperpolarization which in turn served as a pre‐potential for the next spike. The critical level (threshold) for the initiation of the first spike in a train was lower than that of the next and subsequent spikes. 3. A correlation was found between the level of membrane potential and the critical level for action potential generation. This relation was most marked around the resting membrane potential (minus 60 to minus 80 mV) where 10 mV hyperpolarization caused a 9 m V increase in the critical potential level. At higher membrane potentials the correlation was less pronounced. In innervated muscles a similar correlation existed but it was less marked and was present only at membrane polarizations below the resting potential. 4. Increasing the external calcium concentration from 2 to 8 mM reduced the membrane potential‐critical level relationship in denervated fibres towards that of innervated ones. 5. As critical level changes with membrane hyperpolarization, the rate of rise of the action potential increased, suggesting a progressive removal of sodium inactivation. 6. It is suggested that a mechanism similar to anode break excitation is important for the induction and maintenance of fibrillation potentials.
Drinking behaviour in the cat induced by renin, angiotensin I, II and isoprenaline.
Authors: Cooling M J , Day M D
Published: December 2014

1. Angiotensin I, II and hog renin, infused into the lateral cerebral ventricles (I.C.V.) of water replete cats, each induced water drinking behaviour. 2. Intravenous infusion of high doses of angiotensin I or II also elicited a drinking response. The dipsogenic effect of I.V. renin was not marked. 3. Drinking in response to I.C.V. angiotensin II was abolished after autonomic ganglion blockade with I.V. hexamethonium or pempidine and was significantly reduced after I.V. atropine methonitrate. 4. The dipsogenic response to I.C.V. angiotensin II was unaffected by either peripheral adrenergic neurone blockade with I.V. bethanidine, alpha‐adrenoceptor blockade with phentolamine or beta‐adrenoceptor blockade with sotalol. 5. Atropine, atropine methonitrate, hexamethonium and pempidine given I.C.V did not inhibit the diposgenic response to I.C.V. angiotensin II. 6. Bethanidine I.C.V. produced a dose related reduction in the dipsogenic response to I.C.V. angiotensin II. 7. The alpha‐adrenoceptor blocking agents tolazoline and phenoxybenzamine given I.C.V did not affect angiotensin induced drinking but the response was regularly inhibited by phentolamine I.C.V. 8. The beta‐adrenoceptor blocking agents propranolol and practolol given I.C.V. each inhibited angiotensin induced drinking. The L‐isomer of propranolol was a more effective blocker than the D‐isomer. 9. Isoprenaline given I.C.V induced drinking in ten of sixteen cats. Subcutaneous administration of isoprenaline also elicited drinking but the onset of the response was delayed and the amount consumed slightly less than after I.C.V infusion.
Pancreatic acinar cells: ionic dependence of acetylcholine‐induced membrane potential and resistance change.
Authors: Nishiyama A , Petersen O H
Published: December 2014

1. Intracellular recordings of membrane potential, input resistance and time constant have been made in vitro from the exocrine acinar cells of the mouse pancreas using glass micro‐electrodes. The acinar cells were stimulated by acetylcholine (ACh). In some cases ACh was simply directly added to the tissue superfusion bath, in other experiments ACh was applied locally to pancreatic acini by micro‐iontophoresis. 2. Current‐voltage relations were investigated by injecting rectangular de‐ or hyperpolarizing current pulses through the recording micro‐electrode. Within a relatively wide range (−20 to −70 mV) there was a linear relation between injected current and change in membrane potential. The slope of such linear curves corresponded to an input resistance of about 3‐8 M omega. The membrane time constant was about 5–10 msec. 3. ACh depolarized the cell membrane and caused a marked reduction of input resistance and time constant. The minimum latency of the ACh‐induced depolarization (microiontophoretic application) was 100–300 msec. Maximal depolarization was about 20 mV. The effect of this local ACh application was abolished by atropine (1–4 × 10–6 M). The blocking effect of atropine was fully reversible. 4. Stimulating with ACh during the passage of large depolarizing current pulses made it possible simultaneously to observe the effect of ACh at two different levels of resting potential (RP). At the spontaneous RP of about minus 40 mV ACh evoked a depolarization of usual magnitude (15–20 mV) while at the artificially displaced level of about −10 mV a small hyperpolarization (about 5 mV) was observed. It therefore appears that the reversal potential of the transmitter equilibrium potential is about −20 mV. 5. Replacement of the superfusion fluid C1 by sulphate or methylsulphate caused an initial short‐lasting depolarization, thereafter the normal resting potential was reassumed...
Absence of polyneuronal innervation in cat extraocular muscles.
Authors: Bach‐y‐rita P , Lennerstrand G
Published: December 2014

1. Polyneuronal innervation is known to occur in several types of vertebrate muscle, including mammalian muscle spindle (Gray, 1957). Previous work had led to the suggestion that the multiply innervated cat extraocular muscles were similarly polyneuronally innervated. 2. The presence of polyneuronal innervation in fibres that show propagated conduction was explored in the two muscles innervated by the abducens nerve: the lateral rectus (which contains multiply innervated fibres) and the retractor bulbus (which does not). 3. Under conditions of twitch and tetanic stimulation, the sum of individual tensions from the two nerve branches was compared with the tension elicited from the whole nerve. An analysis of variance indicated that the lateral rectus and the retractor bulbus did not differ significantly in terms of tension excess. The twitch condition yielded a small but statistically significant (P smaller than 0–01) amount of tension excess, whereas the tetanic condition did not. 4. Twitches elicited by stimulation of one branch of the abducens nerve showed slight potentiation when preceded by a tetanic stimulation to the other nerve branch. This effect could be ready differentiated from the post‐tetanic potentiation elicited by applying both twitch and tetanic stimuli to the whole nerve. 5. Muscle fatigue produced by intensive stimulation of one nerve branch did not decrease the amplitude of the tetanic contraction elicited by stimulation of the other branch. In fact, instead of crossed fatigue, a small but significant (P smaller than 0–05) potentiation was observed. 6. Analysis of the results of the three tests led to the conclusion that polyneuronal innervation could not be demonstrated in cat extraocular muslce fibers that showed propagated conduction. Thus, the end‐to‐end muscle fibre junctions (Floyd, 1970) apparently do not transmit conducted impulses.