bluuebunny/crossref_metadata_2025_split huggingface dataset:
Membrane properties and inhibitory innervation of the circular muscle cells of guinea‐pig caecum
Authors: Ito Y. , Kuriyama H. 
Published: December 2014

1. The membrane properties of the circular muscle cells of guinea‐pig caecum and nervous factors influencing the muscle activity were studied with micro‐electrodes using partition and field stimulating methods.2. The mean membrane potential was −52 mV. Spontaneous discharges appeared as regular bursts between silent periods, as regular spikes without silent period, or as regular slow potential changes with superimposed spikes.3. Spontaneous spikes with overshoot were frequently observed. The mean maximum rate of rise was 5·2 V/sec. The mean conduction velocity of evoked spikes was 5·4 cm/sec.4. The amplitude of the elctrotonic potential was linearly proportional to the current applied by the partition stimulating method. The spatial decay of the electrotonic potential along the tissue was exponential, with a mean length constant of 1·7 mm.5. The time constants of the membrane calculated from the electrotonic potential, and from the conduction velocity, length constant and time course of the foot of the spike were about 200 and 100 msec respectively. These results indicate that the circular muscle of guinea‐pig caecum possesses cable like properties.6. Field stimulation (0·3 msec pulse duration) to the circular muscle evoked three different responses successively, i.e. initial depolarization (initial excitatory junction potential) with or without spike, hyperpolarization (inhibitory junction potential) and delayed depolarization (delayed excitatory junction potential) with or without spikes.7. These three different potential changes were completely blocked by treatment with tetrodotoxin (5 × 10−6 g/ml.), and both the initial and late excitatory junction potentials were blocked by treatment with atropine (5 × 10−5 g/ml.).8. The distribution of inhibitory nerves in the circular muscle cells was investigated. The results indicate that inhibitory nerves arise from Auerbach's plexus situated just beneath the taenia coli and the nerve branches spread over the whole distance from one taenia coli to the next along the ciruclar muscle cells, a width of about 3 mm.9. The mean conduction velocity of excitation of the inhibitory nerves was 16·0 cm/sec. Hexamethonium, in a concentration of 5 × 10−6 g/ml. depolarized the circular muscle membrane and lowered the rate of rise and fall of spike, but did not block the generation of inhibitory junction potentials.
Some further observations on the electrogenic sodium pump in non‐myelinated nerve fibres
Authors: den Hertog A. 
Published: December 2014

1. A study has been made of the hyperpolarization that follows a period of electrical activity (post‐tetanic hyperpolarization) and of the hyperpolarization which develops when potassium is readmitted after bathing the desheathed vagus nerve of the rabbit in potassium‐free Locke solution during 15 min (potassium‐activated response).2. Reduction of the external chloride concentration increases the membrane resistance and the potassium‐activated response without changing the time constant of the response. A linear relation between the amplitude of the potassium‐activated response and the membrane resistance was found. When chloride was replaced completely by isethionate (sodium salt) and by sulphate (other salts) the potassium‐activated response increased by a factor of 5.3. The membrane resistance is decreased during the post‐tetanic hyper‐polarization elicited in isethionate Locke solution: the decrease is more pronounced after a longer period of electrical stimulation of the nerve.4. A small increase of the membrane resistance was found during the potassium‐activated response. The changed membrane potential during the response can account for the alteration of the membrane resistance observed.5. The amplitude of the potassium‐activated response is increased during hyperpolarization and reduced during external depolarization of the nerve, whereas the time constant is not affected. The potassium‐activated response appears to be independent of polarization of the membrane after correction for the changed membrane resistance.6. The maximum amplitude of the activated response and the external potassium concentration are related following Michaelis—Menten kinetics; the time constant of the response is inversely related to the external potassium concentration.7. The area of the electrogenic response activated by high potassium concentrations (5·6–20 m
M) is almost constant, but is reduced at lower potassium concentrations. The amplitude and area of the thallium‐activated response are increased (about 1·5 times) compared with the potassium‐activated response.8. It was concluded that the electrogenic response, reflected by post‐tetanic hyperpolarization, is not directly related to activity of the electrogenic pump, which is probably due to accumulation of potassium in the periaxonal space; that the potassium activated response is produced entirely by activity of the electrogenic sodium pump; and that the current produced by activity of the electrogenic sodium pump is independent of the electrochemical gradient and membrane resistance.
Calcium entry in response to maintained depolarization of squid axons
Authors: Baker P. F. , Meves H. , Ridgway E. B. 
Published: December 2014

1. Intracellular aequorin was used to monitor changes in Ca entry in response to maintained depolarization either produced electrically or by exposure to K‐rich solutions.2. External K concentrations greater than 50 m
M produce a phasic light response. The light rises to a peak in a few sec and then falls in 0·5‐5 min to a new steady level that is always greater than the level in the absence of K.3. The phasic light response does not result from depletion of available aequorin at the periphery of the axon, but rather seems to reflect a phasic entry of Ca in response to depolarization.4. Similar phasic responses are produced by prolonged electrical depolarization. These results are consistent with depolarization serving both to activate and also to inactivate Ca entry.5. Following inactivation and after return to normal sea‐water, there is an appreciable relative refractory period during which the response both to K‐rich sea‐water and electrical depolarization is reduced in size. Complete recovery takes 10–15 min.6. The response to 410 m
M‐KCl is dependent on the previous treatment of the preparation. Pre‐treatment with 100 or 200 m
M‐KCl reduced the response to 410 m
M‐KCl. The potential for half inactivation was about −25 mV in 112 m
M‐Ca and −40 mV in 20 m
M‐Ca.7. The rate of onset of inactivation is potential dependent and is faster for depolarizations to zero potential than for smaller ones.8. The phasic Ca entry produced by K‐rich solutions is insensitive to external tetrodotoxin and internal tetraethylammonium ions, but is blocked by external Mn2+, Co2+ and Ni2+ ions and by the drugs D‐600 and iproveratril. This suggests that the phasic Ca entry involves the late Ca channel.9. Recovery of the outward K current after a long depolarization is much faster than recovery of the late Ca entry system. This provides further support for the view that the late Ca channel and the K channel are distinct.
Effects of biogenic amines on central thermoresponsive neurones in the rabbit
Authors: Hori T. , Nakayama T. 
Published: December 2014

1. Single unit activities were recorded with five‐barrelled micropipettes from the thermo‐responsive neurones in the preoptic area and the mid‐brain reticular formation in urethanized rabbits. 5‐hydroxytryptamine (5‐HT), noradrenaline (NA) and acetylcholine (ACh) were applied micro‐iontophoretically to the immediate vicinity of the recording cells.2. Out of seventeen warm‐responsive neurones recorded in the preoptic area, fifteen neurones responded to 5‐HT with the increase in firing rate and two showed no response. Thirteen out of seventeen warm‐units decreased their firing rate in response to application of NA and four were not affected. ACh had no effect on any of the warm‐units examined.3. Six out of seven cold‐units in the preoptic area were depressed by 5‐HT, while NA excited five of six units studied. None of the cold‐units were influenced by ACh.4. These results are in good agreement with the changes in rectal temperature produced by 5‐HT and NA micro‐injected into the hypothalamus in rabbits.5. In the mid‐brain reticular formation, 5‐HT excited all of fourteen cold‐responsive neurones. Of these, eight cold‐units were depressed and six were unaffected by NA, while ACh excited six units and had no effect on eight units. All of the five warm‐responsive units were inhibited by 5‐HT and none were influenced by NA. Thus, the responses of reticular thermoresponsive neurones to 5‐HT and NA were opposite to those of the preoptic thermo‐responsive neurones.
Effects of various secretagogues upon 42K and 22Na uptake during in vitro hormone release from the rat adenohypophysis
Authors: Kraicer Jacob , Milligan John V. 
Published: December 2014

1. The in vitro uptake of 22Na and 42K was measured simultaneously in rat adenohypophyses during hormone release produced by several secretagogues and during inhibition of hormone release in Ca‐free media.2. Intracellular adenohypophysial [Na+] and [K+] changed only slightly when the uptake changed. This would indicate that relative permeability changes were the primary effect of the treatments.3. The uptake of 42K was increased by elevated external [K+], but was unaffected by the presence or absence of Ca2+. Acid extracts of hypothalamus‐stalk—median eminence or cerebellum also increased the 42K uptake.4. The uptake of 22Na or 24Na was decreased by elevated [K+]. Uptake was increased in Ca‐free Krebs—Ringer bicarbonate; but was unaltered when [K+] was concurrently increased.5. Neither purified growth hormone releasing hormone, synthetic lysine‐vasopressin, dibutyryl cyclic AMP nor theophylline had an effect on the uptake of either K+ or Na+.6. The rapid uptake of 22Na and its smaller volume of distribution compared to absolute measurements of intracellular [Na+] suggest that the plasma membrane of adenohypophysial cells is relatively impermeable to Na+.7. We conclude that changes in the uptake of Na+ and K+ associated with hormone release are incidental to the release process.8. Hormone release produced by elevated external [K+] is most likely due to a non‐specific increase in permeability of the cell membranes, facilitating Ca2+ entry into the cytoplasm.9. The results suggest that the low resting transmembrane potentials of adenohypophysial cells may be due to their conjoint relatively high permeability to both K+ and Ca2+, rather than K+ and Na+.
The distribution of sodium and potassium in amphibian embryos during early development
Authors: Slack Christine , Warner Anne E. , Warren R. L. 
Published: December 2014

1. Intracellular and intercellular concentrations of sodium and potassium have been measured in pregastrular embryos of Xenopus laevis and Amblystoma mexicanum. Calcium and magnesium contents have also been determined.2. Between egg and gastrula stages of development the potassium concentration is near to 60 m‐mole/l. embryo. Up to the blastula stage the sodium concentration is near to 50 m‐mole/l. embryo; the amount of sodium in the embryo begins to fall just before gastrulation.3. Embryo calcium and magnesium concentrations show no significant variations prior to gastrulation. Average calcium concentrations for the different stages range from 5 to 8 m‐mole/l. embryo; magnesium concentrations lie between 12·4 and 17 m‐mole/l. embryo.4. The intercellular fluid contains 100 m
M sodium and 1 m
M potassium; the majority of the sodium is ionically active. As no net uptake of sodium or potassium occurs before gastrulation these cations must have been transferred from the cells to the cavity.5. At all developmental stages studied, the intracellular potassium concentration is close to 100 m‐mole/l. cell water. Intracellular sodium falls steadily from 80 m‐mole/l. cell water in eggs to 30 m‐mole/l. cell water at the beginning of gastrulation.6. The intracellular sodium activity, measured with sodium sensitive intracellular micro‐electrodes, is relatively constant between egg and blastula stages at about 14 m
M. During each cell division cycle the intracellular sodium activity rises transiently by 2–3 m
M.
Intracellular and intercellular potentials in the early amphibian embryo
Authors: Slack Christine , Warner Anne E. 
Published: December 2014

1. The sensitivity of the membrane potential of cells of early embryos of Xenopus laevis to variations in the extracellular concentrations of sodium and potassium has been determined.2. Alterations in the extracellular sodium concentration have little effect on the membrane potential at all pregastrular stages tested.3. Up to the 32 cell stage an increase in the concentration of potassium in the bathing medium causes a fall in cell membrane potential only when membrane newly synthesized in the furrow during cleavage is exposed at the embryo surface, during the second half of the cell division cycle.4. Beyond the morula stage (48 cells) a fall in membrane potential on raising external potassium can only be demonstrated when the seal which isolates the intercellular fluid from the bathing medium is broken so that cells lining the inner face of the embryo come into contact with the high potassium solution.5. The results suggest that the egg membrane has little selective permeability whereas membrane synthesized after fertilization is highly potassium permeable.6. No evidence could be obtained for any potential difference between the intercellular fluid and the external bathing medium.7. Dinitrophenol, sodium azide and cyanide prevented normal development only if they were injected into the intercellular cavity. Embryos reared in solutions containing these poisons turned into normal tadpoles.8. The formation of the intercellular cavity could be halted by injecting ouabain into the cavity while it was still small. Embryos reared in ouabain turned into normal tadpoles.9. The results suggest that the active transfer of sodium ions from the cells to the intercellular spaces is an integral part of the formation of the intercellular fluid. A hypothesis for the mechanism of formation of the cavity is put forward along these lines.
Biionic potentials in the proximal tubule of Necturus kidney
Authors: Anagnostopoulos Takis 
Published: December 2014

1. Biionic potentials were studied in the proximal tubule of the doubly perfused Necturus kidney and subsequently analysed by means of an equivalent electrical circuit.2. Luminal membrane resistance was found to be at least 3 times greater than peritubular membrane resistance.3. Potassium contribution to peritubular membrane conductance amounts to at least 75%. Replacement of chloride in peritubular circulation by benzene sulphonate or acetyl glycinate hyperpolarized peritubular membrane.4. The peritubular membrane is more permeable to choline than to sodium. Indirect evidence suggests that the opposite may apply at the luminal border.5. The shunt pathway discriminates poorly, if at all, between sodium, potassium and choline, in short term experiments.6. Chloride permeability across the shunt pathway is about three times as great as combined cationic permeabilities.
Rate of uptake of endogenous cortisol by the left ventricle of the anaesthetized dog during ventilation with ambient air and during hypoxia
Authors: Kolanowski J. , Lammerant J. 
Published: December 2014

1. The rate of uptake of endogenous cortisol by the left ventricle was determined in eight dogs as the product of the left ventricular myocardial plasma flow and the coronary arteriovenous difference in plasma cortisol concentration. The arteriovenous difference in hormone concentration in resting skeletal muscle (M. gracilis) was also measured. The values given are means ±
S.E.2. During ventilation with ambient air (arterial PO2: 85 ± 2 mm Hg), the rate of cortisol uptake by the left ventricle averaged 382 ± 92 ng/100 g.min. The arteriovenous difference in hormone concentration in the vessels of the M. gracilis was more than twice that in the coronary vessels. Assuming a value of 3–4 ml./100 g.min for the blood flow in this muscle, the corresponding rate of cortisol uptake would be in the range of 25–33 ng/100 g.min.3. During hypoxia (arterial PO2: 35 ± 1 mm Hg), the rate of cortisol uptake by the left ventricle was not significant, averaging 26 ± 113 ng/100 g.min. By contrast, the skeletal muscle still extracted significant amounts of cortisol from the plasma. It is inferred that the suppression of a significant uptake of the hormone by the left ventricle was related, at least in part, to the changes in the mechanical and associated metabolic activity of the heart muscle elicited by the lowering of the arterial PO2.4. Hypoxia depressed the net uptake of cortisol by the left ventricle rather than the uptake mechanism itself. Indeed, bi‐directional movements of cortisol between the plasma and the heart muscle, with rates of release up to 1150 ng/100 g.min, were observed.
The thermal effects of shortening in tetanic contractions of frog muscle
Authors: Dickinson Valerie A. , Woledge Roger C. 
Published: December 2014

1. In tetanic contractions during which shortening has occurred the total heat produced is greater than in isometric controls.2. The amount of this excess, measured after relaxation, is less than the shortening heat measured before relaxation. In other words relaxation heat is less after contractions with shortening.3. Only a small part of this reduction in relaxation heat can be explained by the reduced thermoelastic heat and work dissipation due to the lower tension maintained after shortening.4. In the few experiments in which the full tension is redeveloped after shortening the relaxation heat is still reduced.5. Decreases in the tension redeveloped after shortening, caused by using shorter tetani, or slower shortening, are not accompanied by decreases in the relaxation heat greater than can be accounted for by the assumed physical results of the lower tension.6. It is suggested that the reduction in relaxation heat after shortening is due to the occurrence of a reaction in which the exothermic process causing the shortening heat is reversed.
The effect of tetanic and post‐tetanic potentiation on facilitation of transmitter release at the frog neuromuscular junction
Authors: Magleby K. L. 
Published: December 2014

1. End‐plate potentials (e.p.p.s) were recorded from frog neuromuscular junctions blocked with high Mg and/or low Ca.2. Estimates of f(t), the facilitation contributed by each impulse, were obtained during and following repetitive stimulation from the incremental change in e.p.p. amplitudes following step changes in the stimulation rate during the conditioning and testing trains.3. Estimates of f(t) increased during the conditioning stimulation and returned to control in the post‐tetanic period. This increase in f(t) was proportional to the magnitude of tetanic or post‐tetanic potentiation (PTP) present.4. These results are described by: [Formula: see text] where h(t)/hc is the e.p.p. amplitude at time t expressed in terms of the control, P(t) is potentiation, F(t) is facilitation and 1 is the base level of transmitter release. Thus, potentiation has a multiplicative (gain) effect on facilitation and the base level of transmitter release.5. PTP was present immediately following the conditioning train. However, if depression occurred during the conditioning train, PTP developed after a delay.6. It is suggested that facilitation and potentiation represent increases in two independent factors which act jointly to increase the probability of transmitter release.
An analysis of the cable properties of spinal motoneurones using a brief intracellular current pulse
Authors: Iansek R. , Redman S. J. 
Published: December 2014

1. A brief intracellular current pulse, with duration less than 500 μsec, has been applied to lumbosacral motoneurones in anaesthetized cats. The resulting voltage transients have been analysed by the procedure suggested in Jack & Redman (1971b) to obtain the cable parameters for each motoneurone.2. Forty‐three motoneurone responses were analysed. In all cases the voltage response indicated that the dendrites could be represented as uniform, finite length cables, with either a sealed distal end, or at least a high resistance distal termination. The electrical length of the equivalent uniform dendritic cable ranged from 1·0 to 2·1 space constants, with a mean value of 1·5.3. The initial decay of the membrane potential following the removal of the current pulse was more rapid than was predicted by the Rall model for the motoneurone, in approximately two thirds of the responses. Consequently a value of dendritic to soma conductance ratio could not be obtained for these motoneurones.4. The explanation given for the departure from the theoretical response to a brief current pulse is that the specific resistivity of the soma membrane is lower than the specific resistivity of the dendritic membrane. This explanation is complicated by the possibility of the electrode tip not lodging in the isopotential soma region. The contribution that each of these effects has on the early decay phase of the current pulse response has been assessed.5. It is concluded that the specific resistivity of the soma membrane could be as low as one third of the dendritic membrane resistivity. Tonic inhibitory activity restricted to the soma is suggested as an explanation.
Alterations in secretory patterns following vagotomy in rats with Pavlov or Heidenhain pouches
Authors: Lundell L. , Svensson S. E. 
Published: December 2014

1. In conscious rats provided with Pavlov or Heidenhain pouches, the acid and pepsin secretion in response to feeding and infusion of gastrin was established before and after truncal vagotomy. In Pavlov pouches the responses to 2‐deoxy‐
D‐glucose, methacholine and the combination of gastrin and methacholine were also studied.2. Interdigestive secretion of acid and pepsin after vagotomy was decreased in the Pavlov pouch and increased in the Heidenhain pouch.3. The acid response to feeding in the Pavlov pouch was substantially reduced after vagotomy, whereas the secretion of pepsin was only slightly diminished.4. In the Heidenhain pouch after vagotomy, feeding augmented the high interdigestive secretion.5. After vagotomy, the acid dose—response curve to gastrin was shifted to the right in the Pavlov pouch and to the left in the Heidenhain pouch.6. In the Pavlov pouch after vagotomy, the acid response to the highest dose of methacholine employed was significantly enhanced.7. A background infusion of methacholine reestablished in the Pavlov pouch the reduced responsiveness to gastrin following vagotomy.8. Pepsin secretion was stimulated by gastrin in the Heidenhain pouch and after vagotomy in the Pavlov pouch. The stimulatory effect of methacholine on pepsin secretion in the Pavlov pouch was increased after vagotomy.