bluuebunny/crossref_metadata_2025 huggingface dataset:
Fusimotor reflexes in triceps surae elicited by natural stimulation of muscle afferents from the cat ipsilateral hind limb
Authors: Appelberg B. , Hulliger M. , Johansson H. , Sojka P.
Published: December 2014

1. Experiments were performed in forty‐one cats anaesthetized with chloralose.

2. The aim of the study was to investigate whether activity in stretch‐sensitive muscle receptors may cause reflex effects in fusimotor neurones.

3. Activity in fusimotor neurones was studied indirectly by recording from primary and secondary muscle spindle afferents of the triceps surae muscle. The mean rate of firing of the afferents as well as either dynamic index (during ramp extension) or modulation (during sinusoidal extension) was determined. This was done under control conditions, with the posterior biceps—semitendinosus muscles relaxed, and under test conditions, with the same muscles extended.

4. All together, seventy‐one primary afferents were studied quantitatively. Pure or predominantly dynamic effects were observed in twenty‐two, pure or predominantly static effects in nine and no statistically significant effects in forty of the units. Amongst seven secondary afferents studied, two showed weak fusimotor activation, the other five were not influenced.

5. Electrical stimulation of the posterior biceps—semitendinosus or medial gastrocnemius nerves at group II strength was observed to cause dynamic fusimotor reflexes on a number of occasions.

6. The reflex effects observed were, on many occasions, recorded in spinalized preparations.

7. The reflex effects were not accompanied by any detectable e.m.g. activity in triceps, as judged from surface e.m.g. recordings. The reflex effects observed are therefore tentatively ascribed to activation of γ‐motoneurones, yet a contribution from β‐motoneurones cannot wholly be excluded.

8. On the basis of available evidence concerning reflex connexions to γ‐motoneurones from various muscle afferents, it is suggested that the effects observed were caused by activation of muscle spindle secondary endings.
Further studies on the mechanism of phosphorylase activation in rabbit liver in response to splanchnic nerve stimulation
Authors: Shimazu Takashi , Usami Mihoko
Published: December 2014

1. The mechanism of activation of liver phosphorylase after splanchnic nerve stimulation has been investigated in rabbits and compared with the effects of intraportal injections of noradrenaline.

2. The increase in the activity of liver phosphorylase‐a, the active form of this key glycogenolytic enzyme, in response to injections of noradrenaline was blocked by β‐adrenergic antagonists, but not by α‐adrenergic antagonists, suggesting that the effect of noradrenaline is mediated mainly through β‐adrenoceptors in vivo. In contrast, the increase in phosphorylase activity in response to stimulation of the peripheral end of the splanchnic nerve was resistant to both α‐ and β‐adrenoceptor blockade.

3. When diltiazem and verapamil, selective Ca2+ antagonists that restrict calcium influx across the cell membrane, were infused intraportally, the phosphorylase response to splanchnic nerve stimulation was virtually abolished, while the response to noradrenaline was unaltered.

4. Infusion of the prostaglandin‐synthesis inhibitor indomethacin at a dose of 3·4 μg/min was found to block the activation of liver phosphorylase in response to stimulation of the splanchnic innervation.

5. These results suggest that the mechanism whereby stimulation of the sympathetic innervation to the liver leads to activation of phosphorylase is not mediated by either α‐ or β‐adrenoceptors, but appears to depend upon prostaglandin formation and influx of Ca2+ ions into the hepatocytes.
Enhancement of ionic currents through voltage‐gated channels in the mouse oocyte after fertilization
Authors: Yamashita Naohide
Published: December 2014

1. The changes of voltage‐gated ion channels in the mouse oocyte after fertilization were investigated under voltage clamp.

2. About 60 min after introduction of sperm suspension into the fertilization medium, the amplitude of inward current through Ca2+‐channels increased, which occurred at anaphase during the second meiotic division. The peak amplitude of the maximum inward current per unit membrane capacity of the oocytes at metaphase was 20±3 μA/μF in 50 mM‐Sr medium. It was 28±8 μA/μF at anaphase, and 32±5 μA/μF at telophase. The kinetic properties as well as selectivity among Ca, Sr and Mn ions were not altered after fertilization.

3. The outward surge current which was found at the higher membrane potential over +50 mV also increased in amplitude after fertilization, simultaneously with the increase in amplitude of inward current through Ca2+‐channels. The means and the standard deviations of the surge current per unit membrane capacity at 120 mV were 31±8 μA/μF at metaphase, and 48±7 μA/μF at telophase. The kinetic properties of the outward surge current were not altered after fertilization.

4. Application of colcemid (10−7 mole/l.) or cytochalasin B (2 × 10−5 mole/l.) did not prevent the increase in amplitude of both inward current through Ca channels and the outward surge current.

5. The membrane currents in N‐18 mouse neuroblastoma cells in logarithmic growth phase were examined under voltage clamp. The N‐18 neuroblastoma cells possessed the Ca inward current and the delayed outward current. The kinetic properties and the steady‐state inactivation of Ca2+‐channels in N‐18 neuroblastoma cells were compared with those in mouse oocytes. It was concluded that they could be regarded as identical between the mouse oocyte and the N‐18 neuroblastoma cell.
Osmotic water flow across the abdominal skin of the toad Bufo marinus: effect of vasopressin and isoprenaline
Authors: de Sousa R. C. , Grosso Alda
Published: December 2014

1. Net water flow Jw, was measured across the abdominal skin of the toad Bufo marinus with a volumetric, automatic technique that allows for averaging Jw over time intervals as short as 1 sec.

2. Basal Jw was very stable and corresponded to a coefficient of osmotic flow, LPD, of ca. 15 × 10−7 cm sec−1 atm−1 (or to an osmotic water permeability coefficient, Pf, of 20 μm sec−1).

3. Both vasopressin and the β‐adrenergic agonist, isoprenaline, triggered high hydrosmotic responses that could lead to Pf values exceeding 250 μm sec−1. The effect of isoprenaline was very reproducible while that of vasopressin varied considerably.

4. Methohexital and propranolol selectively inhibited the hydrosmotic effects of vasopressin and isoprenaline, respectively, whereas amiloride and ouabain had no effect.

5. Mutual inhibition was found between vasopressin and isoprenaline in skins very sensitive to vasopressin. In less sensitive skins isoprenaline further increased Jw despite exposure of the epithelia to supramaximal concentrations of vasopressin.

6. Differential reactivity to vasopressin was found between the skin and the bladder taken from the same toad. In some instances, the bladder responded normally to vasopressin while the skin was totally unresponsive, suggesting the presence of osmoregulatory mechanisms exerting a local modulation of the vasopressin action in different target epithelia of the same animal.
Adaptation of cardiac vagal responses to baroreceptor stimuli in the dog
Authors: Potter Erica K.
Published: December 2014

1. There is adaptation of the cardiac vagal efferent responses to stimulation of the arterial baroreceptors by a series of brief intracarotid pressure pulses, by a sustained elevation of pulsatile systemic pressure, or by sustained steady increases in intracarotid pressure. This was demonstrated here in experiments on anaesthetized dogs.

2. Trains of brief intracarotid pressure pulses were delivered to carotid baroreceptors at varying interstimulus intervals. Reflex bradycardia was evoked by the first stimulus of a train but as succeeding stimuli were placed closer to those preceding them they became less effective in evoking reflex bradycardia. This attenuation of the heart rate response was not due to attenuation of the responses of baroreceptor nerve endings to repeated brief stimuli, or to reflex changes in systemic blood pressure.

3. Activity in single cardiac vagal efferent fibres was recorded in response to pairs of intracarotid pressure pulses, to step changes in non‐pulsatile carotid blood pressure, and to changes in pulsatile systemic blood pressure. Adaptation of cardiac vagal discharge over a period of 10 sec or more, to both pulsatile and non‐pulsatile increases in blood pressure, was shown.

4. The slow time course of the adaptation of vagal discharge makes it most unlikely that it can be completely accounted for by adaptation of the baroreceptor nerve endings themselves. Therefore, the results obtained here are taken to indicate that adaptation occurs centrally, along the baroreceptor to vagal pathway.
Effects of nystatin‐mediated intracellular ion substitution on membrane currents in calf Purkinje fibres
Authors: Marban Eduardo , Tsien Richard W.
Published: December 2014

1. Calf cardiac Purkinje fibres were exposed briefly to the ionophore nystatin to promote exchange of caesium for intracellular potassium. The effects of Cs loading were stable for at least 30 min, but they could be reversed by nystatin‐mediated K loading.

2. After Cs loading, the resting potential shifted to about ‐20 mV and the current—voltage relationship showed a strong inhibition of inwardly rectifying K channels.

3. Anodal break stimulation evoked normal action potential upstrokes and twitch contractions. The early repolarization (phase 1) was markedly slowed.

4. Cs loading simplified the pattern of current changes evoked by step depolarizations over the plateau range. Membrane current reached an inward peak and then declined monotonically.

5. The current signal showed no hint of the transient outward current found in untreated or K‐loaded preparations. Furthermore, Cs loading abolished the outward tails associated with deactivation of transient outward current, and occluded the blocking effect of the K‐channel inhibitor 4‐aminopyridine.

6. Inhibition of transient outward current revealed a maximal inward current of about 5 μA/μF in 5·4 mM‐Cao, which is considerably larger than the net inward current without Cs loading.

7. The inward current was attributed to Ca channels on the basis of its sensitivity to membrane potential, extracellular Ca, D600, Mn and Cd.

8. Cs loading also reduced slow current changes associated with delayed rectification and pace‐maker depolarization.

9. The results support the hypothesis that the transient outward current is carried by K+ ions, while providing a method for unmasking inward Ca current.
The development of the segmental pattern of skin sensory innervation in embryonic chick hind limb
Authors: Scott Sheryl A.
Published: December 2014

1. The development of dermatomes in the chick hind limb was investigated with both electrophysiological recording from and horseradish peroxidase (HRP) labelling of neurones in lumbosacral dorsal root ganglia (d.r.g.s). The embryonic stages studied spanned the period before and after cell death.

2. In mature embryos, after the bulk of cell death, physiological mapping showed that the location of the dermatome of each d.r.g. is consistent from embryo to embryo. HRP studies showed that axons from each d.r.g. project through the limb to the skin via a characteristic set of nerve trunks. Both the dermatomes and axonal projection pathways of adjacent d.r.g.s partially overlap one another, producing an orderly progression in the location of dermatomes and projection pathways along and within the limb, respectively.

3. In younger embryos, before cell death, the location and amount of overlap of dermatomes, as well as the axonal projection pathways, are similar to the mature pattern. D.r.g.s that innervate distal skin on the shank and foot in mature embryos do not project out cutaneous nerve trunks in the thigh or contact nearby skin on the thigh at earlier stages.

4. Axons from a single d.r.g. initially contact the skin at one or more characteristic spots; the dermatomes then enlarge, adding fine axonal branches.

5. Carbon‐marking experiments showed that there are no large distal migrations of skin on the limb during the stages studied.

6. Together these findings show that dermatomes on the chick hind limb do not develop by skin sensory axons simply growing to the nearest available skin, nor are axons towed to their final location by skin movements. Moreover, dermatomes are not shaped by cell death and the elimination of random or excessive axonal projections in the limb or the skin. It appears that skin sensory axons from each d.r.g. grow directly to their target skin along a defined set of pathways and establish their dermatome precisely at its characteristic location.
The electrogenic sodium pump in guinea‐pig ventricular muscle: inhibition of pump current by cardiac glycosides
Authors: Daut Jürgen , Rüdel Reinhardt
Published: December 2014

1. The inhibition of the electrogenic sodium pump in guinea‐pig ventricular muscle by cardiac glycosides was studied with a voltage‐clamp technique.

2. Superfusion of the preparation with dihydro‐ouabain (DHO) produced a reversible depolarization of up to 7 mV. When the membrane potential was clamped to a constant value near the resting potential application of DHO produced a corresponding current change in the inward direction which reached a steady state in less than 1 min.

3. The drug‐induced current change (ID) was found to be the result of a parallel shift of the current—voltage relation. The contributions of a change in extracellular K or intracellular Na to the measured ID were shown to be very small. From these findings and the results summarized below it was concluded that ID represents the blockage of the electrogenic pump current by DHO and that it is proportional to the number of drug molecules bound to the Na—K‐ATPase in the intact cell.

4. The dependence of ID on the concentration of DHO applied (5 × 10−6‐8 × 10−4 M) was found to be consistent with the predictions of the law of mass action for reversible one‐to‐one binding of the drug to the Na—K pump under equilibrium conditions. From a Scatchard‐type plot the equilibrium dissociation constant (KD) of DHO was determined to be 4·6 (±2·3) × 10−5 M.

5. The steady‐state pump current in the resting preparation was calculated to be 0·81±0·26 μA/cm2. It contributed 6·4±0·9 mV to the resting potential in Tyrode solution containing 3 mM‐K.

6. In the smallest preparations used the measured time course of the onset and decay of ID agreed with the chemical kinetics of binding and unbinding calculated for various DHO concentrations. The rate constant of unbinding (k2) was found to be 3·4 (±0·7) × 10−2 S−1 and the average rate constant of binding (k1) was 7·4 × 102 M−1 S−1.

7. By comparing the effects of ouabain and DHO in the same preparation the following estimates of the chemical constants of ouabain binding to the Na—K pump were obtained: KD ≃ 1·5 × 10−6 M; k1 ≃ 4 × 103 M−1 S−1; k2 ≃ 6 × 10−3 S−1.

8. An analysis of the transmembrane movements of Na and K in the steady state showed that the measured pump current density is consistent with a counter‐transport of 3 Na and 2 K ions.
Calcium inactivation in skeletal muscle fibres of the stick insect, Carausius morosus.
Authors: Ashcroft F M , Stanfield P R
Published: December 2014

1. Inactivation of Ca currents in skeletal muscle fibres of the stick insect, Carausius morosus, was studied using a three‐electrode voltage‐clamp method. 2. The extent of inactivation showed a voltage‐dependence similar to that of the Ca current, inactivation being absent in the absence of a Ca current, maximal at potentials where Ca currents are largest, and reduced at potentials close to ECa. 3. Ca currents inactivated along a double exponential time course, both when measured from the decline of Ca current during a single pulse and when measured using a two pulse protocol. In 20 mM‐Ca‐Ringer the fast time constant of inactivation had a mean value of 27 msec and that of the slow time constant was 134 msec, at O mV and 5 degrees C. 4. The rate of inactivation was slowed, and its extent reduced, in low [Ca]o, where Ca currents are smaller. Similarly, inactivation was faster and more complete in high‐Ca‐Ringer. 5. The rate of recovery from inactivation also followed a double exponential time course, with time constants of 638 msec and 4 sec following a 500 msec inactivating pulse in 20 mM‐Ca‐Ringer at 5 degrees C. Recovery appeared to be related to the amount of Ca entry during the inactivating pulse, being slower in high [Ca]o and following longer inactivating pulses. 6. Inactivation was slowed and reduced in extent when Ba2+ or Sr2+ carried current. Inactivation in Ba solutions may be due to depletion of Ba2+ from the lumen of the transverse tubules. 7. Ba2+ does not compete with Ca2+ for the inactivation mechanism. 8. It is concluded that inactivation of Ca currents in stick insect muscle fibres is primarily mediated by Ca2+ entry.
The response of the hind‐limb vascular bed of the rabbit to sympathetic stimulation and its modification by pregnancy.
Authors: Humphreys P W , Joels N
Published: December 2014

1. Pressure‐flow relationships in the hind limb, perfused with blood at a series of constant flows, have been compared in primigravid and virgin rabbits following section of the lumbar sympathetic chain. 2. In the absence of sympathetic stimulation perfusion pressure was lower (P less than 0.05) in the pregnant rabbits at all levels of flow to the leg. 3. It is concluded that pregnancy leads to a reduction in the vascular resistance of the acutely sympathectomized hind limb. 4. The pressure‐flow curves of hind limbs from pregnant and non‐pregnant rabbits in which the cutaneous circulation had been excluded by skinning the leg and ligating the ankle were also compared. Again, perfusion pressure at each flow level was lower in the limbs from the pregnant animals (P less than 0.05). 5. The sympathetic supply was stimulated at frequencies of 0.3, 1, 3, 7, 15 and 30 Hz. Irrespective of whether the cutaneous circulation was excluded, the pressure‐flow curves for the hind limbs of pregnant and non‐pregnant rabbits were different at the lower frequencies. As stimulus frequency rose this difference became smaller, and at a stimulus frequency of 7‐15 Hz or more there was little difference in the position of the curves in pregnant and non‐pregnant rabbits. 6. Examination of the pressure‐flow curves suggests that when, as in these experiments, flow is held constant, the ability of sympathetic stimulation to increase the resistance to blood flow is reduced in pregnancy. However, if these pressure‐flow curves are used to predict the change of flow that would occur at a constant perfusion pressure, the response to sympathetic stimulation appears to be greater in pregnancy. 7. Further analysis of the findings, based on certain assumptions, suggests that differences between the pressure‐flow curves of pregnant and non‐pregnant animals during sympathetic stimulation are due in the main to either a differing size of the unstimulated vascular beds or a differing compliance of their vessel walls, rather than to any intrinsic alteration in their response to sympathetic stimulation.
Effects of a small serosal hydrostatic pressure on sodium and water transport and morphology in rabbit gall‐bladder
Authors: Eldrup E. , Frederiksen O. , Møllgård K. , Rostgaard J.
Published: December 2014

1. In order to investigate the mechanism of serosal pressure‐induced inhibition of isosmotic fluid transport, the effect of 4·5 cm water serosal pressure on spontaneous water transfer (Jv) in rabbit gall‐bladders was measured (in the presence of a supporting soft nylon net on the mucosal side) in a modified Ussing chamber. This allowed unidirectional Na+ fluxes ([Formula: see text] and [Formula: see text]), transepithelial potential difference and resistance (Rt) to be measured simultaneously. The effects of the serosal pressure were also investigated by light and electron microscopy.

2. During pressure application, Rt increased due to a covering effect of the mucosal support. The serosal pressure caused a parallel decrease in Jv and net Na+ transport ([Formula: see text]) across the free epithelial surface of 80‐85%. About 85% of the decrease in [Formula: see text] was due to a decrease in [Formula: see text].

3. After inhibition of 93% of fluid absorption by serosal 10−3M‐ouabain, pressure‐induced change in Jv was only 8% of the spontaneous fluid transport rate.

4. Control Na+ flux ratio ([Formula: see text]) was 3·5. The pressure‐induced increase in steady‐state [Formula: see text] of 30‐35% therefore contributed little to the decrease in [Formula: see text]. Further, this increase in [Formula: see text] was completely prevented by mucosal 10−3 M‐amiloride.

5. All pressure‐induced effects on transport and electrical parameters were reversible.

6. The light microscopical and scanning electron microscopical results showed that half of the epithelial surface was covered by the nylon net following serosal pressure application. Ruptures in the epithelium were not seen. Thin section and freeze fracture electron microscopy demonstrated continuous, well developed tight junctions both in control and experimental condition.

7. It is concluded that a serosal pressure of only 4·5 cm water causes inhibition of a cellular active Na+ and water transport with only minimal, if any, contribution from paracellular filtration. This would seem incompatible with the concept that an active ion transport mechanism localized in the basolateral cell membrane is responsible for transepithelial fluid transport. The possibility of a mechanical fluid transport mechanism via elements of a tubulo‐cisternal endoplasmic reticulum is raised.
Enhanced chemosensitivity of chick parasympathetic neurones in co‐culture with myotubes.
Authors: Crean G , Pilar G , Tuttle J B , Vaca K
Published: December 2014

1. The influence of target interaction upon the electrophysiological properties of dissociated ciliary ganglion cells was investigated by testing the sensitivity of the neuronal somal membrane to ionophoretically applied acetylcholine (ACh). Variations in the percentage of cells responsive to the transmitter were measured with time in culture. 2. Twenty‐four hours after plating, all cells respond to an ionophoretic pulse of ACh with a depolarization. However, 1 week after plating (between 7 and 14 days) most of the neurones are unresponsive, and highly responsive cells (greater than 100 mV peak depolarization/nC) are extremely rare. At even later times in culture, neurones sensitive to the transmitter are again more frequent. 3. When neurones are plated onto pre‐formed pectoral myotubes, however, ACh sensitivity is maintained throughout a 3 week culture period. Neuromuscular junctions are formed by the neurones, and when sufficient neurones are present, all the muscle fibres tested show evidence of functional synaptic transmission. Chemosensitivity to ACh is not maintained by neurones in muscle‐free microcultures are present on the same cover‐slip. 4. Interneuronal synaptic contacts, defined by ultrastructural criteria, are formed in cultures of neurones alone, but evidence of widespread functional synaptic interaction between cells was not found at 7‐14 days in culture. 5. It is concluded that the maintenance of ACh sensitivity of cultured ciliary ganglion cells is enhanced by the presence of muscle in co‐culture. The interneuronal synaptic contacts observed are apparently not as potent a stimulus as co‐culture with muscle for the full expression of the cholinergic phenotype under these culture conditions.
Dichroic components of Arsenazo III and dichlorophosphonazo III signals in skeletal muscle fibres
Authors: Baylor S. M. , Chandler W. K. , Marshall M. W.
Published: December 2014

1. Absorbance changes were measured following stimulation of single muscle fibres injected with the metallochromic indicator dye Arsenazo III. Two dye‐related signals can be clearly resolved: (1) an early, transient isotropic signal that appears to be due to the formation of Ca2+:dye complex and (2) a slower, transient signal that is ‘dichroic’ in nature. The dichroic signal is obtained by taking the difference between absorbance changes measured with light plane polarized along the fibre axis (0° light) and at right angles to the axis (90° light).

2. The time course of the dichroic signal is the same at all wavelengths employed, suggesting that a single underlying process is involved. The wavelength dependence of the magnitude of the signal is similar to that obtained for dye absorbance in a resting fibre.

3. At 570 nm, near the isosbestic wavelength for changes in H+:dye, Mg2+:dye and Ca2+:dye, the dichroic signal is near maximal. The absorbance change with 0° light is positive and is about twice as large as the change with 90° light, which is negative. This finding is consistent with the idea that the dichroic signal arises from dye molecules which change their orientation in the radially symmetric muscle fibre. The direction of the change is for the dye's transition moment to become more aligned with the fibre axis during activity.

4. During a train of ten action potentials the (isotropic) Ca2+ transient increases in magnitude three‐fold, whereas the dichroic waveform reaches a plateau value only 30‐40% larger than the single twitch value.

5. Replacing H2O in Ringers with D2O causes a slight reduction in the Ca2+ signal, reduces the dichroic signal to 0·4 times normal, and reduces tension to 0·1 times normal. Qualitatively similar reductions were found to accompany an increase in osmolality of H2O Ringer from 1 × to 2·5 × normal.

6. Dichroic signals are also observed in fibres injected with Dichlorophosphonazo III. These are similar in many respects to the Arsenazo III dichroic signals.

7. With Arsenazo III, the dichroic signal probably arises from a reorientation of some dye molecules which are bound to one of the oriented structures in muscle. The reorientation lags the Ca2+ transient and may be due to a change which occurs in the oriented structure itself. Using this idea, the Arsenazo III dichroic signal can be fitted by assuming that Ca2+ ions bind to receptor sites and that this binding induces the required change in the oriented structure. The analysis indicates that the hypothetical receptors have a dissociation constant for Ca2+ equal to 0·1‐1 times the peak value of myoplasmic free [Ca2+] during a twitch and an ‘off’ rate constant equal to 10‐30 sec−1 at 15 °C.
Properties of single calcium‐activated potassium channels in cultured rat muscle
Authors: Barrett J. N. , Magleby K. L. , Pallotta B. S.
Published: December 2014

1. Properties of the Ca‐activated K channel were studied in excised patches of surface membrane from cultured rat muscle cells using single channel recording techniques.

2. Increasing the concentration of calcium at the intracellular membrane surface [Ca]i, increased both the frequency and effective duration of channel openings. Ca at the extracellular membrane surface was not sufficient to activate the channels.

3. An approximate third power relationship (slope = 2·7) was observed between [Ca]i and the percentage of time the channels spent in the open state.

4. Both the frequency and effective duration of channel openings increased as the intracellular membrane surface was made more positive; the percentage of time spent in the open state increased e‐fold for a 15 mV depolarization for low levels of activity.

5. The percentage of time spent with 1, 2,...n channels open in membrane patches with n channels was described by the binomial distribution, suggesting that the channels opened and shut independently of one another.

6. Single channel conductance (144 mM‐K on both sides of the membrane) was essentially independent of membrane potential (‐50 to +50 mV) and [Ca]i (0·1 μM ‐1 mM), but did increase with temperature, from 100 pS at 1 °C to 300 pS at 37 °C.

7. Channel activity occurred in apparent bursts, with the duration of the apparent bursts increasing with increasing [Ca]i.

8. Two exponentials were required to describe the distribution of observed channel open times, suggesting two different open channel states of apparently normal conductance. The observed mean channel open time of these states at +30 mV was 0·34 and 2·2 msec with 0·1 μM‐Cai and was 0·47 and 6·9 msec with 0·5 μM‐Cai.

9. The channel occasionally entered an apparent third open channel state with a single channel current amplitude about 40% the amplitude of the normally observed single channel currents. The reduced conductance state was immediately preceded and followed by a normal conducting state.

10. While the kinetics of the Ca‐activated K channel appear complex, its large conductance and high Ca and voltage sensitivity suggest that it is uniquely suited to resist depolarizations of the cell membrane potential that are accompanied by increases in intracellular Ca.
Voltage‐activated and calcium‐activated currents studied in solitary rod inner segments from the salamander retina
Authors: Bader C. R. , Bertrand D. , Schwartz E. A.
Published: December 2014

1. Solitary rod inner segments were obtained by enzymatic dissociation of the tiger salamander (Ambystoma tigrinum) retina. Their membrane currents were studied with the single‐pipette voltage‐clamp technique. Individual currents were isolated with the aid of pharmacological agents.

2. Extracellular caesium blocked a current activated by hyperpolarization from ‐30 mV. Changing external sodium and potassium concentrations altered the value of the reversal potential in a manner consistent with the current being carried equally by both ions.

3. Extracellular tetraethylammonium (TEA) blocked a current activated by depolarization from ‐70 mV. In normal medium this current had a reversal potential of ‐72 mV. Changing the external potassium concentration altered the value of the reversal potential in a manner consistent with the current being carried predominantly by potassium.

4. Extracellular cobalt blocked a current activated by depolarization that had an initial inward and a later outward component.

5. After EGTA was injected into an inner segment the outward component was suppressed. Cobalt then blocked an inward current. This current is believed to be carried predominantly by calcium. The conductance increased with depolarization from ‐45 mV and reached a maximum at approximately 0 mV. Following a step of depolarization the current activated rapidly (< 20 msec) and then remained constant for at least several seconds without evidence of inactivation.

6. Injecting caesium into an inner segment eliminated a calcium‐activated outward current believed to be carried by potassium ions.

7. After the injection of caesium there remained another calcium‐activated current with a reversal potential of ‐17 mV. Changing extracellular chloride concentration altered the value of the reversal potential in a manner consistent with chloride carrying at least 70% of the current. Another anion may carry the balance.

8. When the five currents mentioned in items 2, 3, 5, 6 and 7 were blocked, the membrane resistance between ‐90 and ‐25 mV was linear, time‐independent, and had a high value (2·1 GΩ).

9. The five identified currents can all be activated in the physiological range of voltage in which salamander rods normally operate.
Blocking kinetics of the anomalous potassium rectifier of tunicate egg studied by single channel recording
Authors: Fukushima Yasuo
Published: December 2014

1. The kinetics of the anomalous K current produced by blocking cations Na, Cs and Sr were analysed by single channel recording in the tunicate egg cell.

2. The open—close kinetics in a single channel with the presence of blocking cation were consistent with the blocking kinetics of the total anomalous K current. The open—close kinetics in a single anomalous K rectifier channel could be regarded as the first order transition between the open and closed states.

3. The closing rate constants of the single channel for the first order transition increased almost linearly on a semilogarithmic scale as the membrane potential became more negative, while the opening rate constants decreased and then increased, showing the minimum at a certain potential level. The latter indicated that the channel was released from the blocking by excessive hyperpolarization.

4. The opening rate constant increased in spite of the fixed concentration of the blocking cation (10 μM‐Cs), when the external K concentration was raised from 200 mM to 400 mM. This result suggested that there are interactions within the channel between the blocking cation and the K ion.

5. When there were two kinds of blocking cations such as Na and Cs, the kinetic properties in a single channel indicated that the two kinds of blocking cations blocked the single channel independently.

6. The single channel conductance of the anomalous K rectifier in 200 mM‐Na‐containing 200 mM‐K solutions was about 1·5 times larger than that in Na‐free 200 mM‐K solutions.

7. The single channel conductances in 100, 200 and 400 mM‐K solution with 10 μM‐Cs were 5·0, 7·1 and 12·3 pS respectively, being roughly proportional to the square root of the K concentration.

8. The density of the anomalous K rectifier channel in the tunicate egg cell was 0·039/μm2.

9. The amplitude of the single channel current increased with the rise of temperature, the Q10 being 1·5.
Closely coupled excitation of γ‐motoneurones by group III muscle afferents with low mechanical threshold in the cat
Authors: Ellaway P. H. , Murphy P. R. , Tripathi Anita
Published: December 2014

1. The reflex responses of γ‐motoneurones to discharges of muscle receptors innervated by Group III axons have been examined in hind‐limb muscles of decerebrated and spinal cats.

2. Electrical stimulation of the gastrocnemius medialis nerve at a strength sufficient to excite Group III axons caused excitation of gastrocnemius lateralis or soleus γ‐motoneurones. The excitation was more prominent in the spinal animal.

3. Excitation of either silent or tonically firing γ‐motoneurones was a secure, driven type of response consisting of one or two spikes occurring at fairly fixed latency in response to a single stimulus. Eighteen out of thirty‐nine γ‐motoneurones studied showed such excitation.

4. Subtracting peripheral conduction times of the γ‐motoneurone impulse and the earliest component of the Group III volley from the latency of reflex excitation gave a range of central delays of 1·8‐4·8 msec (mean 3·0 msec).

5. Inhibitory Group III effects were also seen but were less pronounced than the excitation.

6. The origin of the receptors connected to the Group III axons whose discharge causes driven excitation of γ‐motoneurones was investigated.

7. Isometric twitch contractions of a muscle caused pronounced facilitation or excitation of homonymous and heteronymous γ‐motoneurones. Excitation occurred close to the peak or during relaxation of the twitch with a range in latency of 30‐110 msec. The muscles studied were triceps surae, flexor digitorum and hallucis longus.

8. Pressure or light taps applied to the gastrocnemius medialis muscle caused an increase in discharge frequency in twenty out of twenty‐eight γ‐motoneurones of the same muscle (four were inhibited). The response to a steady stimulus adapted but could outlast it by many seconds. Pressure was more effective when applied to the proximal or distal parts of the muscle.

9. Fifteen out of thirty‐eight gastrocnemius medialis receptors having Group III axons (conduction velocities 5‐27 m/sec) were found to discharge one, or occasionally two, spikes to twitch contractions of the parent muscle at latencies of 30‐80 msec.

10. Eight out of ten receptors with Group III axons that responded to contraction had low thresholds to pressure and taps, whereas the majority of the twenty‐three Group III units which were insensitive to contraction had high thresholds to such stimuli. Receptive fields of all Group III units were confined to either the proximal third or distal third of gastrocnemius medialis or, in a few instances, the Achilles tendon.

11. We conclude that discharges in Group III axons from receptors which respond to non‐noxious, low threshold mechanical stimuli cause a tightly coupled excitation of γ‐motoneurones. The likely contribution of this reflex to the control of movement is discussed.
Intrinsic noise in locust photoreceptors.
Authors: Laughlin S B , Lillywhite P G
Published: December 2014

1. In locust photoreceptors, the amplitude of the response to light pulses lasting less than 20 ms depends solely upon the number of absorbed photons, which can be estimated at low intensities by counting quantum bumps. Consequently, each receptor can be operated as a calibrated photon counter. 2. Three types of noise in receptor responses have been identified‐‐extrinsic or photon noise and two types of intrinsic noise, dark noise (spontaneous activity) and transducer noise (noise in the transduction mechanism). The methods by which the noise sources are measured and identified involves measuring the responses to a train of flashes of constant intensity and converting these voltage values into a series of equivalent quantum catches. Because photon absorptions follow the Poisson distribution, the variance among equivalent catches due to photon noise equals the mean catch, and any excess variance represents intrinsic noise. 3. Dark noise is negligible: spontaneous signals (quantum bumps produced in darkness) occur less than ten times per hour at 25 degrees C, and the combined effects of membrane and electrode noise are unimportant at all but the highest intensities. 4. At low intensities transducer noise is responsible for more than 50% of all receptor noise (variance), and this rises to 90% when bright stimuli are presented to the dark‐adapted eye. 5. Two simple models of transduction indicate that variations in the amplitudes and latencies of responses to single photons are a major source of transducer noise. 6. Transducer noise would be difficult to detect from an analysis of response noise alone, without knowledge of absolute photon catch, because in some important respects it mimics photon noise, e.g. it lowers the quantum efficiency without violating the square root relationship relating increment thresholds to mean intensity.
Evidence that the contractile response of the guinea‐pig ileum to capsaicin is due to release of substance P.
Authors: Barthó L , Holzer P , Lembeck F , Szolcsányi J
Published: December 2014

1. The possible roles of substance P and opioids in the contractile response of the isolated guinea‐pig ileum to the sensory stimulant drug capsaicin were investigated, and the contractions were found to be inhibited by about 60% in preparations desensitized to substance P. 2. Contractions evoked by stimulation of the mesenteric nerves in the presence of the adrenergic blocking drug guanethidine were inhibited by about 75% after the ileum had been rendered insensitive to substance P. 3. Atropine partially inhibited the effect of capsaicin. The atropine‐resistant component of the contractile response to capsaicin was inhibited by more than 85% in preparations desensitized to substance P and almost abolished by the substance P antagonist, (D‐Pro2,D‐Trp7,9)‐substance P. 4. The opioid peptide (D‐Met2, Pro5)‐enkephalinamide inhibited, whereas the opiate antagonist naloxone enhanced the atropine‐resistant contractions in response to capsaicin. 5. The results indicate that the contractile response of the guinea‐pig ileum to capsaicin and mesenteric nerve stimulation is mediated by release of substance P, presumably from sensory nerve endings in the gut. Substance P appears to act on the smooth muscle both directly and indirectly via cholinergic neurones. It is proposed that opioids modulate the non‐cholinergic response to capsaicin by inhibiting the release of substance P.
The influence of the sympathetic nervous system on individual vessels of the microcirculation of skeletal muscle of the rat
Authors: Marshall Janice M.
Published: December 2014

1. Direct observations have been made on the responses of individual vessels of the microcirculation of rat spinotrapezius muscle to stimulation of the sympathetic paravascular nerve fibres and to topically applied catecholamines.

2. All arteries and arterioles were constricted by sympathetic stimulation, the maximum response occurring at a stimulus frequency of 8‐10 Hz. Primary and secondary arterioles (13‐50 μm internal diameter) showed the greatest percentage change in diameter and remained constricted throughout the 1 min stimulation period whilst terminal arterioles (7‐13 μm internal diameter) constricted initially but then returned towards their control diameter before the stimulus ceased.

3. By contrast the venules and veins showed no response to sympathetic stimulation.

4. In accord with these observations, fluorescence histochemical studies revealed a network of noradrenergic nerve fibres on all arterial vessels but showed no innervation of any venous vessels.

5. Topically applied noradrenaline or adrenaline (10−10‐10−8 g/ml.) dilated the majority of arteries and arterioles while higher concentrations of either agent produced dose‐dependent constrictor responses. In addition, many venules dilated in response to adrenaline (10−9 g/ml.) while others constricted, but concentrations of either noradrenaline or adrenaline greater than 10−8 g/ml. produced dose‐dependent constriction of all venules and veins.

6. The behaviour of the more proximal and more distal arterioles during sympathetic stimulation is in accord respectively with the changes in muscle vascular resistance and in capillary surface area recorded in previous studies during sympathetic stimulation.

7. The observation that venous vessels are not influenced by sympathetic nerve fibres contrasts with the established view that venous vessels of skeletal muscle are strongly constricted during sympathetic stimulation. However, reappraisal of the evidence used to support this view indicates that such results may have been misinterpreted, while other available evidence supports the proposal that the present findings may be representative of skeletal muscle vasculature in general.
The inhibitory effect of the olivocerebellar input on the cerebellar Purkinje cells in the rat†
Authors: Montarolo P. G. , Palestini M. , Strata P.
Published: December 2014

1. In rats under Nembutal anaesthesia the inferior olive region has been reversibly inactivated by applying a cooling probe to the ventral surface of the medulla. Simple and complex spike activity has been recorded from Purkinje cells of the cerebellar cortex.

2. Following cooling of the inferior olive of one side we have observed a remarkable increase of the simple spike activity in all the twenty‐two Purkinje cells, showing a disappearance of the complex spike activity.

3. In some rats two Purkinje cells were recorded simultaneously from each side of the cerebellar cortex. Following cooling of the left inferior olive the effect on the Purkinje cell was observed only or predominantly on the contralateral cerebellar cortex.

4. In a group of animals the inferior olive has been destroyed by 3‐acetylpyridine 4‐221 days before the recording session. Cooling of the inferior olive region was not accompanied by any significant and consistent increase in the spike activity of presumed Purkinje cells of the contralateral cerebellar cortex.

5. These results indicate that the remarkable increase of the simple spike frequency following cooling of the inferior olive region is due specifically to the suppression of the activity of the olivocerebellar neurones.

6. Only a small amount of the simple spike frequency increase is attributable to the removal of the post‐climbing fibre pause.

7. In some lesioned rats recording was made from Purkinje cells, which showed complex spikes due to the few surviving inferior olive cells. In these Purkinje cells cooling of the inferior olive region was accompanied by a disappearance of the complex spike and by a small increase of the simple spike frequency of discharge. Such an increase is mainly attributable to the removal of the post‐climbing fibre pause.

8. These results suggest that a given Purkinje cell is not only under the inhibitory influence of its own climbing fibre, but also of other olivocerebellar neurones, probably through climbing fibre collaterals to the cerebellar cortical interneurones.

9. It is suggested that one role of the olivocerebellar system is to exert a powerful tonic inhibitory action on the Purkinje cells and consequently to exert a significant control on the excitability of the subcerebellar centres.
Effect of barbiturates on the GABA receptor of cat primary afferent neurones
Authors: Higashi H. , Nishi S.
Published: December 2014

1. The effects of the barbiturate anaesthetics, pentobarbitone and thiopentone, on the membrane properties and the γ‐aminobutyric acid (GABA)‐induced responses of cat primary afferent neurones were studied with intracellular recording and voltageclamp techniques.

2. At low concentrations (10−7‐10−5 M) both barbiturates slightly enhanced and prolonged GABA‐induced depolarizations or currents without affecting the membrane properties. At these concentrations, barbiturates have no effect on the apparent dissociation constant of the GABA‐GABA receptor interaction or the reversal potential for GABA‐induced depolarizations or currents.

3. At high concentrations (10−4‐10−3 M) barbiturates produced a few millivolts reduction in the resting membrane potential. Voltage‐clamp analysis revealed that the depolarization was associated with one of the three types of conductance change, i.e., an initial increase followed by a decrease (40% of neurones examined), only an increase (40%) and only a decrease (20%).

4. Analysis in different ionic media indicated that the depolarization with a reduced membrane resistance is associated with an increased chloride conductance and that the one with an increased membrane resistance is accompanied by a reduction in potassium conductance. Bath‐application of GABA (10−3 M) or picrotoxin (10−5 M) inhibited the increase in chloride conductance but not the reduction in potassium conductance.

5. Barbiturates at these high concentrations initially caused a marked augmentation and prolongation of GABA responses; this was followed by a depression. The depressant action did not appear to be voltage‐dependent. These actions of barbiturates were not accompanied by changes in the apparent dissociation constant of the GABA‐current dose—response curve or the reversal potential for GABA currents. In addition, the single exponential decay of GABA current was not changed despite a marked prolongation of its decay time.

6. Picrotoxin (10−5 M) antagonized the depressant effect of barbiturates at high concentrations on GABA currents, and barbiturates (5 × 10−6 M) reduced the inhibitory action of picrotoxin (5 × 10−6 M) on the GABA‐currents.

7. From all these results, it is suggested that the site of barbiturate actions on GABA‐responses is mainly the allosteric site (the ionic conductance regulatory subunit) but not the agonist recognition site or the chloride channels linked with GABA receptors.