bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hyperpolarizing effects of dopamine on chemoreceptor nerve endings from cat and rabbit carotid bodies in vitro
Authors: Sampson S. R. , Vidruk E. H. 
Published: December 2014

1. The effects of dopamine on DC potential changes recorded from the carotid sinus nerve were studied in vitro using carotid bodies and associated sinus nerves removed from anaesthetized cats and rabbits.2. The carotid body was placed in one compartment of a superfusion chamber and was superfused with buffered salt solution. The carotid sinus nerve was led into an adjoining compartment, containing lightweight mineral oil, for recording DC potential changes with chlorided silver electrodes.3. Dopamine injected into the superfusing solution in amounts of 50‐250 μg caused hyperpolarization of the DC potential. This effect occurred repeatedly in each preparation, the maximum number of tests in any one preparation being twenty‐seven.4. In the same preparations, acetylcholine (50‐100 μg) and NaCN (10‐20 μg) caused depolarizations of the DC potential, effects that have been described by others.5. The hyperpolarizing effects of dopamine were reduced or abolished by the α‐adrenergic antagonists, dihydroergotamine (10‐100 μg/ml.) and phenoxybenzamine (5 μg/ml.) and the dopamine antagonist droperidol (10‐25 μg/ml.).6. The results indicate that the inhibitory effects of dopamine on the frequency of carotid body chemosensory discharges in cats and rabbits are due to hyperpolarization of chemoreceptor afferent nerve endings and not necessarily to local vascular effects in the carotid body.
Voltage jump analysis of procaine action at frog end‐plate
Authors: Adams P. R. 
Published: December 2014

1. In the absence of procaine the end‐plate conductance evoked by suberyldicholine increases exponentially to a new level following a step hyperpolarization. In the presence of procaine the suberyldicholine‐evoked conductance first rapidly decreases and then slowly increases following a hyperpolarizing step. The fast relaxation has a time constant of ∼ 1 msec, and the slow relaxation a time constant of 10‐150 msec.2. The existence and sign of these two relaxations is predicted by a sequential model in which procaine enters and blocks open but not closed end‐plate channels. The concentration dependence of the fast and slow relaxation time constants agrees well with the predictions of this model, and allows the apparent dissociation constant for binding of procaine within the open channel to be estimated at about 20 μ
M at ‐80 mV membrane potential.3. This apparent binding constant is voltage sensitive. It decreases e‐fold for 50 mV hyperpolarization, suggesting that the procaine binding site is electrically half way through the channel.4. Procaine concentrations comparable to the dissociation constant for binding to open channels strongly depress the equilibrium current evoked by low suberyldicholine concentrations. This finding is not in accord with the sequential model.5. A cyclic model in which procaine binds to both closed and open channels explains well the equilibrium observations. The affinity of procaine for closed channels is similar to its affinity for open channels, and is also increased by hyperpolarization. This model also fits well the kinetic observations, if it is assumed that blocked channels open and close much more slowly than unblocked channels.6. The concentration dependence of the relaxation amplitudes disagrees with the predictions of the sequential model, but agrees well with the predictions of the cyclic model.7. No other model appears to explain the various observations as economically as the cyclic channel blocking model. If the model is correct the ‘gate’ controlling the end‐plate channel must be in the inner half of the membrane.
Caffeine and the contractility of single muscle fibres from the barnacle Balanus nubilus
Authors: Ashley C. C. , Ellory J. C. , Griffiths P. J. 
Published: December 2014

1. In single striated muscle fibres from the barnacle Balanus nubilus tension development following axial injection of caffeine (50 m
M in 150 m
M‐KCl, pH 7·1) was used as an index of releasable Ca. It was shown that fibres incubated in 0 Ca (Na replaced) salines for up to 400 min gave ca. 15% of the control tension response. Inclusion of 1 m
M‐La in the 0 Ca (Na) saline significantly reversed this decline.2. Estimates of the total fibre calcium assayed under the same experimental conditions indicated a 67% loss of fibre Ca in 0 Ca, and only a 37% loss in La‐0 Ca media. No correction was made for the loss of calcium from the extracellular space.3. Experiments with 45Ca indicated that the efflux of calcium from this preparation was inhibited by 1 m
M‐La externally and that this effect was still significant even in the presence of 0 Ca (Na) salines. The caffeine‐stimulated efflux of Ca was also reduced by ca. 70% in the presence of 1 m
M La saline externally.4. The influx and efflux of 14C caffeine were shown to be rapid, and apparently passive. The diffusion coefficient for caffeine following intracellular injection was 2·4 ± 0·2 × 10−6 cm2 sec−1 at 18‐22° C.5. There was no significant loss of 140La over a period of 2 hr following axial micro‐injection into the fibres.6. In 140La uptake experiments there was a progressive increase in the La space over 10·5 hr, in contrast to the results with [3H]inulin, whose uptake saturated in ca. 1·5 hr. The probability of surface binding and the precipitation of La salts in the extensive extracellular space was suggested as an explanation.7. It is concluded that internal Ca within the sarcoplasmic reticulum, and not cleft or extracellular Ca is the most significant source for these caffeine‐induced contractions. Fluxes across the surface membrane can however alter the internal Ca stores over longer periods of time.
Membrane properties and conduction velocity in sensory neurones following central or peripheral axotomy
Authors: Czéh G. , Kudo N. , Kuno M. 
Published: December 2014

1. The properties of dorsal root ganglion cells in the lumbosacral segments were examined with intracellular electrodes about 3 weeks after section of the central (dorsal roots) or peripheral processes in the cat.2. Chronic section of the peripheral nerve in the hind limb resulted in a reduction in conduction velocity of both the central and peripheral processes of sensory neurones.3. Sensory neurones arising from the triceps surae and plantaris muscles were subject to ‘disuse’ conditions for about 3 weeks by section of the ventral roots combined with severance of the Achilles tendon. Under such conditions, the central and peripheral conduction velocities of these sensory neurones tended to decrease, but the decrease was significantly less than that following peripheral nerve section.4. Chronic section of the dorsal roots produced no significant changes in conduction velocity of the central processes of muscle sensory neurones but caused a significant increase in the peripheral conduction velocity.5. The only electrophysiological property of dorsal root ganglion cells which altered following axotomy was the time‐dependent membrane rectification in response to hyperpolarizing current pulses. The rectification characteristics were modified by chronic section of the peripheral nerve but not by chronic section of the dorsal root.6. It is concluded that injuries in nerve fibres per se do not necessarily result in a decrease of their conduction velocity and that a decrease in their conduction velocity is associated with changes in the properties of the cell bodies.7. It is suggested that a decrease in conduction velocity following nerve section may require the participation of changes in the neurone cell body.
Short circuit current and total conductance measurements on rat ileum
Authors: Emílio M. Graça , De Jesus C. Henriques 
Published: December 2014

1. Short circuit current and total conductance measurements were made on preparations of rat terminal ileum, using either the intact tissue or the isolated epithelium.2. The effects of
D‐glucose, 3‐O‐methyl‐
D‐glucose, and 3‐deoxy‐3‐fluor‐
D‐glucose, added in suitable concentrations to the external bathing medium, were studied.3. An increase in both short circuit current and total conductance was detected when these sugars were used. It was possible to determine a linear relationship between the two variables and to study the kinetics of the interaction of glucose and 3‐O‐methyl‐
D‐glucose with the sodium sugar carrier by using increasing concentrations of these substances.4. The increases in short circuit current and total conductance were also verified in isolated epithelium.5. Phlorizin, or the withdrawal of glucose, reversed the increase in short circuit current, but the total conductance remained unchanged.6. Increasing concentrations of 2‐deoxy‐
D‐glucose added to the mucosal bathing medium caused a decrease in short circuit current without changing the total conductance, either in preparations of intact ileum or in isolated epithelium.7. The meaning of these variations in the electrical parameters of the preparations is discussed.
Nasal field loss in kittens reared with convergent squint: neurophysiological and morphological studies of the lateral geniculate nucleus
Authors: Ikeda Hisako , Plant G. T. , Tremain K. E. 
Published: December 2014

1. Recordings of single cells were made in layers A and A1 of the lateral geniculate nucleus of kittens raised with convergent squint in one eye, and morphological studies of cells representing the different parts of the visual fields in these layers were also made from histological sections.2. For the normal eye, cells receiving inputs from the nasal and temporal visual fields were evenly represented up to the periphery, whereas for the squinting eye, no cells which permitted quantitative studies of receptive field properties could be found in the periphery of the nasal field.3. The loss of nasal field, represented by the loss of functional cells in the LGN layer A1 fed by the squinting eye, depended on the severity of the squint. The greater the angle of convergent squint, the greater the loss of nasal field represented by the loss of functional cells.4. The cells fed by the squinting eye's temporal visual field retained their brisk function, although minor modifications in the receptive field organisation were apparent.5. The mean perikaryal size was smaller and the cell‐density higher for cells in layers fed by the squinting eye. As found for the functional loss of cells, the shrinkage of perikaryal size and the increase of cell‐density was smallest in the zones fed by the temporal visual field, and greatest in the zones fed by the peripheral nasal visual field.6. The functional and morphological changes in the cells in the LGN, which receive inputs from the nasal field of the squinting eye, are attributed to part of the temporal retina being hidden behind the bridge of the nose. It is proposed that this is a consequence of disuse atrophy, due to lack of stimulation during the sensitive period of development.
A comparison of the energy balance in two successive isometric tetani of frog muscle
Authors: Curtin Nancy A. , Woledge Roger C. 
Published: December 2014

1. Measurements were made of the energy produced as heat and work (h + w) and the chemical changes which occurred between the beginning and end of each of two periods of stimulation. The muscles contracted tetanically under isometric conditions. Each period of stimulation (tetanus) lasted 5 sec and there was an interval of 3 sec between them. The tension developed in the second tetanus was 91% of that in the first.2. The observed (h + w) was greater in each tetanus than the quantity expected from the measured chemical changes. This excess was 230 ± 43 mJ/g dry wt. (mean ±
S.E. of mean) in the first tetanus, but only 89 ± 46 mJ/g in the second tetanus (mean ±
S.E. of mean). The result for the first tetanus agrees with previous findings.3. The observed (h + w) was divided into two parts, labile and stable, which were defined by Aubert (1956). This division was made on the basis of the time course of the (h + w) production, without reference to the chemical changes. The labile part of the (h + w) has an exponentially declining rate, and the stable part has a constant rate.4. The observed (h + w) was less in the second tetanus than in the first. This was due largely to the decrease in the labile part in the second tetanus; it was only ca. 0·35 of that in the first tetanus. However, the stable part remained relatively constant, 0·83 of that in the first tetanus. Aubert & Maréchal (1963) and Aubert (1968) have reported similar results.5. Having divided the (h + w) into the stable and labile parts, we found that the stable part could be accounted for by the chemical change, but the labile part could not. Thus, for both tetani, the stable part of the energy is about equal to the explained energy, and the labile part is about equal to the unexplained energy. The possible interpretations of these equalities are discussed.
Collecting duct flow rate as a determinant of equilibration between urine and renal papilla in the rat in the presence of a maximal antidiuretic hormone concentration
Authors: Lote C. J. , Snape B. M. 
Published: December 2014

1. Antidiuretic hormone (ADH) was infused into normal male rats at a rate of 60 μu./min. 100 g body wt., to maintain an effectively constant maximal circulating level. Four groups of rats were used; they were water‐loaded by receiving together with the ADH,
I.V. infusions of hypotonic dextrose (2·5 g/100 ml.) at different rates (1·0, 4·5, 9·0 and 12 ml./hr, respectively), over an infusion period of 4 hr.2. Urine flow rate increased in all groups, the rate and extent of the increase being related to the volume rate of infusion. The differences in urine flow rates between the four groups were due almost entirely to increases in free water clearance, with no consistent differences in osmolal clearance between the groups. At the end of the 4 hr infusion period, osmolal clearances were closely similar in the four groups.3. Papillary and medullary tissue solute concentrations were progressively reduced at the higher rates of infusion. The changes were due to small increases in the water content, together with a profound decrease in urea concentration and a smaller decrease in sodium concentration. However, papillary osmolality was consistently higher than urine osmolality at the three highest rates of dextrose infusion.4. As urine flow rate increased, there was a progressive reduction in the degree of osmotic equilibration between the final urine and the papillary tip. For urea, however, the degree of equilibration remained high.5. It is concluded that, in the rat, the rate of flow per se, along the collecting duct, is an important determinant of final urine concentration; even if there is an osmotic driving force for water re‐absorption in the renal medulla, and the collecting duct walls are permeable to water, osmotic equilibration is restricted by tubular flow rate.
An analysis of the actions of prostaglandin E1 on membrane currents and contraction in uterine smooth muscle (rat)
Authors: Grosset Alain , Mironneau Jean 
Published: December 2014

1. The effects of prostaglandin E1 have been studied on the transmembrane potentials, ionic currents, and contractions in isolated myometrial strips from pregnant rats by means of a double sucrose gap apparatus.2. At low concentrations (10−8 g/ml.), prostaglandin E1 reduced the duration (though not the amplitude) of the action potential, but significantly increased the contraction. The inward current was unchanged, as well as the phasic component of the contraction. However, the tonic contraction, recorded when the transmembrane calcium influx was blocked selectively with D 600, was stimulated significantly, and the outward current secondarily increased.3. At maximally effective doses (10−6 g/ml.), the electrical response to prostaglandin E1 consisted of a slight depolarization, while a large contracture developed. The depolarization and contracture were unaffected by the removal of external calcium. The inward current was reduced by prostaglandin E1 and the reversal potential was shifted towards less positive values of voltage, indicating a decrease in the driving force and consequently, an increase in the internal calcium concentration.4. Dibutyryl‐c‐AMP (5 × 10−4
M) produced a marked relaxation of the resting tension and a slight hyperpolarization of the uterine membrane. Under these conditions, a triggered action potential was able to evoke a larger contractile response. However, prostaglandin E1 is known to increase tissue c‐AMP, so that its contractile effect cannot be mediated by c‐AMP.5. It is suggested that prostaglandin E1 acts essentially by increasing the intracellular calcium concentration. This might result from the translocation of membrane‐bound calcium from surface microvesicles or sarcoplasmic reticulum. The increase in internal calcium concentration could, in turn, lead to an increase in the outward current intensity.
Movement of strontium ions into mast cells and its relationship to the secretory response
Authors: Foreman J. C. , Hallett M. B. , Mongar J. L. 
Published: December 2014

1. Non‐stimulated mast cells take up 89Sr and 45Ca. There is a rapid phase of uptake of both labels which is complete in 1 min and the 89Sr uptake is similar in magnitude to the 45Ca uptake. A further slower phase of uptake occurs in the period from 1 to 30 min of incubation. The magnitude of this slower phase is about 6 times greater for 89Sr than for 45Ca.2. Non‐stimulated and antigen‐stimulated mast cells accumulate Sr which can be measured by atomic absorption spectroscopy. There is a direct relationship between Sr accumulation and histamine secretion which is independent of whether or not the cells are stimulated. 10% histamine secretion is associated with Sr accumulation of 0.25 f‐mole/cell.3. The time course of 89Sr uptake is similar to the time course of histamine secretion in non‐stimulated cells.4. The uptake of 89Sr is linearly related to the external Sr concentration in the range 0.5‐16 m‐mole/l. for both stimulated and non‐stimulated cells.5. Ca, 10‐1000 μmole/l. inhibits 89Sr uptake in non‐stimulated cells.6. Inhibition of glycolysis and oxidative phosphorylation prevents spontaneous histamine secretion in the presence of Sr without blocking the accumulation of Sr by the cells.7. Dibutyryl cyclic AMP, 10 m‐mole/l. produces only 18% inhibition of 89Sr uptake whereas histamine secretion is inhibited by 45% by the same concentration. The antigen‐stimulated Sr uptake on the other hand can be completely inhibited by dibutyryl cyclic AMP, 10 m‐mole/l.8. The uptakes of 89Sr and Sr by unstimulated mast cells after 60 min incubation are dependent on extracellular H ion concentration. Both uptakes increase with increasing pH over the range pH 7‐8.5.
Membrane currents underlying activity in frog sinus venosus
Authors: Brown Hilary F. , Giles Wayne , Noble Susan J. 
Published: December 2014

1. The spontaneous electrical activity of small strips of muscle from the sinus venosus region of the heart of Rana catesbeiana was investigated using the double sucrose gap technique. The voltage clamp was used to record the ionic currents underlying the pace‐maker depolarization and the action potential.2. The records of spontaneous electrical activity are very similar to those obtained from the sinus venosus using micro‐electrodes. Moreover, the pace‐maker activity is almost completely insensitive to tetrodotoxin (TTX) at 2·0 × 10−6 g/ml., which suggests that the pace‐maker responses can be classified as primary, as opposed to follower pacing.3. In response to short rectangular depolarizing voltage clamp pulses, only one inward current is activated. This current is almost completely insensitive to TTX but can be blocked by manganese ions. It appears, therefore, to be equivalent to the slow inward (Ca2+/Na+) current, Isi, of other cardiac tissues. The threshold for Isi is near to the maximum diastolic potential, indicating that it must be activated during the pace‐maker depolarization.4. Interruption of the normal pace‐maker depolarization by rapid activation of the voltage clamp circuit reveals the time‐dependent decay of outward current. This current reverses between ‐75 and ‐90 mV and, therefore, is probably carried mainly by potassium ions.5. Outward current decay is not a simple exponential, and Hodgkin—Huxley analysis suggests that two distinct components of outward current may be present. One of these is activated in the potential range of the pace‐maker depolarization and the other at more positive potentials. Both outward currents reach full, steady‐state activation at about zero mV, i.e. within the ‘plateau’ range of the sinus action potential.6. These results are compared with other recently published voltage clamp data from the rabbit sino—atrial node.7. A hypothesis for the generation of pace‐maker activity is presented which involves (i) decay of outward current and (ii) activation of the slow inward current, Isi.
Sodium entry in rat diaphragm induced by depolarizing drugs
Authors: Creese R. , Franklin G. I. , Mitchell L. D. 
Published: December 2014

1. An increased uptake of labelled sodium was found in the end‐plate region of rat diaphragm following brief exposure to solution containing 24Na plus carbachol (100 μ
M), with a wash in inactive saline. Tetrodotoxin (0·1 μ
M) was also present. Comparable results were obtained with decamethonium and suberyldicholine.2. With carbachol (100 μ
M) the influx of labelled sodium at the end‐plate region was increased by a factor of at least three as compared with that at the end of the fibres.3. After entry the labelled sodium spread along the fibres with an apparent diffusion coefficient which was half that expected in the external solution.4. The dose—response curve for the effect of carbachol gave a half‐maximal value of 72 μ
M.5. In muscles depolarized by potassium methyl sulphate the effect of carbachol on the entry of sodium was reduced although demonstrable.6. The entry of labelled sodium at the end‐plate was maintained during prolonged exposure to carbachol (100 μ
M) or decamethonium (100 μ
M).7. The rate of entry of 24Na obtained with carbachol, after corrections for the wash, was estimated as 1·5 × 103 ions channel−1 sec−1, measured over a period of 15 sec.8. Labelled decamethonium and labelled carbachol also accumulated at the end‐plate region. After extrapolation to allow for the effects of the wash the entry of decamethonium when expressed as a clearance (pl. mg−1 sec−1) was comparable to that of sodium, as expected if decamethonium and sodium enter through the same channels.