bluuebunny/crossref_metadata_2025 huggingface dataset:
Increased microvascular resistance to blood flow in the rat hindlimb after perfusion with neuraminidase.
Authors: Born G V , Palinski W
Published: December 2014

1. The ability of blood to flow through capillaries with diameters smaller than that of erythrocytes and leucocytes has been explained hypothetically on the basis of electrostatic repulsion between vessel walls and circulating cells, but in the absence of in vivo evidence. Following our discovery of extraordinarily high densities of sialic acids on endothelial surfaces, we have now devised experiments to determine to what extent microcirculatory blood flow might depend on these negative charges. 2. Hindlimbs of rats anaesthetized with ether and pentobarbitone were perfused through the femoral artery at constant volume with continuous recording of inflow resistance: first with carotid arterial blood containing continually infused acetylcholine at concentrations which minimized peripheral resistance without affecting heart rate; then for 5 min with buffered saline containing acetylcholine at the same concentration plus neuraminidase (from Vibrio cholerae, at 0.1 mg/ml) to remove endothelial sialic acids (for control experiments without neuraminidase); and then again with acetylcholine‐infused carotid blood. 3. As a consequence of the saline perfusion, there was a rapid initial rise and fall of inflow resistance. The subsequent changes in resistance were calculated as the difference between its lowest value in the first 10 min and the value after 60 min. Controls and neuraminidase‐perfused groups were compared using the t test for unpaired measurements. 4. In four control experiments inflow resistance decreased by 10‐40% (14 +/‐ 10%, mean +/‐ S.E.M.). In three experiments with neuraminidase, inflow resistance increased by 24‐38% (29 +/‐ 4%, mean +/‐ S.E.M.). The difference between the saline and the neuraminidase‐perfused groups was significant (P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)
Kinetics of phototransduction in retinal rods of the newt Triturus cristatus.
Authors: Forti S , Menini A , Rispoli G , Torre V
Published: December 2014

1. The kinetics of photoresponses to flashes and steps of light of rods, from the retina of the newt Triturus cristatus, were analysed by recording the membrane current with a suction electrode. 2. In dark‐adapted conditions the relation between the normalized amplitude of the photoresponse at a fixed time 1 s after the onset of light and the light intensity could be fitted by an exponential or a polynomial relation. In the presence of a steady bright light the same relation could be fitted by a Michaelis‐Menten relation. 3. The kinetics of photoresponses to light stimuli was reconstructed using a model in which: (i) three molecules of guanosine 3'.5'‐cyclic monophosphate (cyclic GMP) open a light‐sensitive channel; (ii) light activates the enzyme phosphodiesterase, which hydrolyses cyclic GMP, thus closing light‐sensitive channels: (iii) Ca2+ ions permeate through light‐sensitive channels: and (iv) intracellular Ca2+ inhibits, in a co‐operative way, the enzyme cyclase, which synthesizes cyclic GMP. 4. The model reproduces the shortening of the time to peak of brief flash photoresponses from about 1080 ms to about 690 ms with brighter lights. The model also explains the shortening of the time to peak to 350 ms observed in the presence of a steady light and the lack of a further acceleration with brighter flashes of lights. 5. The presence in the model of an intracellular calcium buffer accounts for the partial reactivation of the photocurrent following a step of light, lasting several seconds. The time course of this reactivation is not accelerated by a steady bright light both experimentally and in the model. 6. After the extinction to a long step of light the photocurrent showed a rapid partial reactivation, which was followed by a slow component of the photoresponse which extinguished with a rate constant of about 0.05 s‐1. The model explains the origin of this slow component by assuming that the inactivation of excited rhodopsin is partially reversible. 7. The model is also able to explain the particular changes of kinetics when different amounts of exogenous calcium buffers are incorporated into rods (Torre, Matthews & Lamb, 1986).
The Mg2+ block and intrinsic gating underlying inward rectification of the K+ current in guinea‐pig cardiac myocytes.
Authors: Ishihara K , Mitsuiye T , Noma A , Takano M
Published: December 2014

1. The blockade by Mg2+ and intrinsic gating of the channel, which underlie the rectification of the inward rectifier K+ current, was investigated using the oil‐gap voltage clamp method in isolated guinea‐pig ventricular cells. 2. The inward rectifier K+ current was isolated by subtracting trans‐gap currents recorded at an extracellular K+ concentration ([K+]o) of 0 mM from those obtained at 14 mM [K+]o in the presence of a given concentration of intracellular Mg2+ ([Mg2+]i). The reversal potential (V0) of the difference current was near the equilibrium potential for K+ (EK). 3. On repolarization across EK, the inward rectifier K+ current showed a rapid exponential increase. The time constant decreased with increasing hyperpolarization, but it was independent of both [Mg2+]i and the preceding depolarization. 4. When the pre‐pulse potential was made progressively positive between V0‐20 and V0 + 30 mV, the amplitude of the time‐dependent component became larger and the preceding current jump decreased at any [Mg2+]i. With pre‐pulses more positive than V0 + 40 mV, the time‐dependent component started from almost the zero current level at 2 microM [Mg2+]i. At higher [Mg2+]i (350, 500 and 3000 microM), however, the time‐dependent component became smaller as the pre‐pulse potential was made more positive than V0 + 40 mV. 5. When the membrane was depolarized from a potential of full activation at 2 microM [Mg2+]i, the initial jump in the outward current was ohmic and was followed by an exponential decay. The time‐dependent component of the inward current, recorded on repolarization after increasing durations of the preceding depolarization, developed as the outward current decayed. The time constants of both processes were in good agreement. 6. At 500 microM [Mg2+]i, the outward current on depolarization was instantaneously rectified. The time‐dependent component recorded on repolarization developed with prolongation of the pre‐pulse with a time course slower than at 2 microM [Mg2+]i. The envelope time course became slower as the potential of the depolarization became more positive. 7. Lowering the temperature from 23 to 15 degrees C slowed the time‐dependent current with an apparent Q10 of about 3.5 at V0. 8. Based on the experimental data, kinetic parameters were estimated for a model of Mg2+ block, which well simulated the inward‐going rectification of the K+ current. 9. It is concluded that the instantaneous inward rectification on depolarization is due to the Mg2+ block at physiological [Mg2+]i.(ABSTRACT TRUNCATED AT 400 WORDS)
Pattern of monosynaptic Ia connections in the cat forelimb.
Authors: Fritz N , Illert M , de la Motte S , Reeh P , Saggau P
Published: December 2014

1. In anaesthetized cats intracellular records were obtained from antidromically identified motoneurones. The motor nuclei to the elbow extensor and flexor muscles and to the muscles innervated by the deep radial, ulnar and median nerves were investigated. The maximum Ia EPSPs from electrical stimulation of various peripheral nerves were measured. The characteristic convergence and projection patterns to each motor nucleus were established from pooled data. 2. The total aggregates of the Ia EPSPs between the different motor nuclei ranged from 3.5 to 11.7 mV. The smallest aggregates were found in the nuclei to the digit muscles. The ratio of the heteronymous versus homonymous EPSP amplitudes varied between 3.9 and 0.5. A general rule which would govern the distribution of the EPSP aggregates, such as a proximo‐distal gradient, was not observed. 3. The Ia connections followed a complex but highly organized pattern. Bidirectional and unidirectional pathways were present. In many cases the convergence pattern of a motor nucleus included muscles acting at different joints. The connections of one nucleus were not necessarily restricted to one side of the limb, but could cross the radio‐ulnar plane. 4. Muscles with similar actions onto the same joint were interconnected with bidirectional, rather balanced Ia pathways. Such relations were also present between close functional synergists and then often extended across several joints. The relations between the anatomical extensors of wrist and digits were graded according to the neighbourhood of these muscles. It is suggested that this reflects the graded mechanical synergism in the wrist action of these muscles. 5. A large number of unidirectional or strongly skewed bidirectional Ia pathways project from proximal to distal muscles. It is suggested that they may serve a readjustment of distal joints during changes in the position of proximal ones (e.g. stabilization of the position of the radio‐ulnar plane during elbow extension in case of the undirectional projections onto supinator and abductor pollicis longus motoneurones). 6. The motor nuclei to some multifunctional muscles display a negative correlation between different heteronymous Ia inputs: motoneurones with a large input from one muscle show a significant tendency to receive a smaller input from another muscle and vice versa. This organization leads to subpopulations of neurones with different convergence patterns within the same motor nucleus. 7. Motor nuclei with bidirectional Ia relations between each other displayed similar convergence and projection patterns. They were combined into ‘Ia synergistic groups.’ One motor nucleus may belong to several groups.(ABSTRACT TRUNCATED AT 400 WORDS)
Extracellular pH in the isolated retina of the toad in darkness and during illumination.
Authors: Oakley B , Wen R
Published: December 2014

1. Extracellular pH (pHo) was measured in the isolated retina preparation of the toad, Bufo marinus, using H(+)‐selective microelectrodes. During superfusion with phosphate‐buffered solution (pH 7.8), which had a low buffering capacity, pHo in the inner retina was 7.0‐7.2 and there was a pHo gradient throughout the distal retina and into the bathing solution. 2. The retinal acidity appears to be due in part to the combined reactions of glycolysis and ATP hydrolysis, since anoxia greatly increased the pHo gradient, while superfusion with either glucose‐free pyruvate solution or strophanthidin decreased this gradient. 3. Maintained illumination evoked both an acidification in the proximal retina and an alkalinization in the distal retina. Blocking synaptic transmission to second‐order neurones (1.0 mM‐aspartate) decreased the acidification but had little effect on the alkalinization, consistent with the notion that the alkalinization is of receptoral origin, while the acidification is of post‐receptoral origin. 4. Retinal neurones extrude a significant amount of acid via Na(+)‐H+ exchange, since 2.0 mM‐amiloride, a blocker of Na(+)‐H+ exchange, caused a sustained alkalinization in darkness and decreased the light‐evoked changes in pHo, while 1.0 mM‐4‐acetamido‐4'‐isothiocyanatostilbene‐2.2'‐disulphonic acid (SITS), a blocker of Cl(‐)‐HCO3‐ exchange, produced a much smaller alkalinization. 5. Switching to a bicarbonate‐buffered solution having a 75 times greater buffering capacity than the phosphate‐buffered solution caused retinal pHo to become less acidic and significantly decreased the amplitude of the light‐evoked pHo changes. 6. Addition of 2.0 mM‐acetazolamide, a carbonic anhydrase inhibitor, to the bicarbonate‐buffered solution increased both the pHo gradient and the light‐evoked changes in pHo. These data are consistent with the idea that carbonic anhydrase, which is concentrated in Müller (glial) cells and to a lesser extent in horizontal cells, increases the effectiveness of the bicarbonate buffer system. 7. Switching from bicarbonate‐buffered to phosphate‐buffered solutions attenuated the b‐wave of the electroretinogram, most likely by acidifying pHo. Overall, our results emphasize the importance of the bicarbonate buffer system in buffering pHo during periods of variable acid extrusion in light and in darkness.
Rheogenic sodium‐bicarbonate co‐transport across the retinal membrane of the frog retinal pigment epithelium.
Authors: La Cour M
Published: December 2014

1. Na+ and HCO3‐ transport across the retinal membrane of the frog retinal pigment epithelium was studied by means of double‐barrelled Na(+)‐ and pH‐selective microelectrodes. Transient changes in the intracellular pH and in the intracellular Na+ activity were monitored in response to abrupt changes in the Na+ concentration and in the HCO3‐ concentration on the retinal side of the epithelium, and in response to transepithelial currents. 2. Removal of Na+ from the retinal side of the epithelium caused a depolarization of the membrane potential across the retinal membrane, a decrease in the intracellular Na+ activity and a decrease in the intracellular pH. 3. An increase in the HCO3‐ concentration on the retinal side of the epithelium from 27.5 to 50 mM caused a hyperpolarization of the membrane potential across the retinal membrane, an increase in the intracellular Na+ activity and an increase in the intracellular pH. 4. Passage of a transepithelial current of 30 microA in the choroid‐to‐retina direction caused an increase in the intracellular Na+ activity and an increase in the intracellular pH. 5. The data are interpreted as evidence for rheogenic co‐transport of Na+, HCO3‐ across the retinal membrane of the frog retinal pigment epithelium. 6. The transient changes described under 2, 3 and 4 above were blocked by 0.5 mM‐4‐acetamido‐4'‐isothiocyanostilbene‐2.2'‐disulphonic acid (SITS). The Na(+)‐ HCO3‐ co‐transport was not inhibited by 1 mM‐amiloride.
Argiopine blocks glutamate‐activated single‐channel currents on crayfish muscle by two mechanisms.
Authors: Antonov S M , Dudel J , Franke C , Hatt H
Published: December 2014

1. The effect of the spider venom argiopine on L‐glutamate‐activated membrane channels of crayfish muscle was investigated using the patch‐clamp technique. 2. When 10(‐2) M‐glutamate and 10(‐9) M‐argiopine were contained in the pipette solution of a cell‐attached patch, bursts of openings of excitatory channels appeared after formation of the patch. These bursts ceased abruptly after variable periods of time in the range of 5 min. Higher concentrations of argiopine (up to 10(‐6) M) blocked more rapidly, approximately in proportion to concentration. 3. The block of excitatory channels could be partially or completely reversed by hyperpolarizing the membrane by up to ‐190 mV from the resting potential. The time constant of the recovery of channel opening decreased with increasing hyperpolarization and was 2 ms with ‐160 mV hyperpolarization. Switching back from the hyperpolarized level to the resting potential, the time constant for the resulting block was about 3 s (10(‐7) M‐argiopine). Potential‐dependent block by argiopine with similar characteristics was also observed in outside‐out patches. 4. Up to argiopine concentrations of 10(‐7) M the kinetics of channel openings and of bursts measured in pre‐block periods or during reversal of the block by hyperpolarization were indistinguishable from controls. 5. When the potential‐dependent block observed in the presence of 10(‐6) M‐argiopine and 10(‐2) M‐glutamate was reversed by hyperpolarization, additional short closings occurred during bursts. This ‘flickering block’ did not change burst length appreciably, but an additional open time component (tau = 0.1 ms) appeared and the average open time per burst was reduced. 6. At least two reaction steps seem necessary to model the behaviour of the potential‐dependent block. The flickering block may be described as intermittent blocking of the channel which does not interfere with the reactions between glutamate and the channel.
ATP‐activated channels gate calcium entry in single smooth muscle cells dissociated from rabbit ear artery.
Authors: Benham C D
Published: December 2014

1. A combination of the techniques of microspectrofluorimetry and whole‐cell patch clamp was used to investigate changes in cytoplasmic Ca2+ concentration (Cai2+) in single arterial smooth muscle cells on external application of ATP. 2. ATP applied to cells held under voltage clamp at ‐‐60 mV evoked an inward current and an associated rise in Cai2+. In the absence of extracellular Ca2+. ATP‐activated inward currents were observed but there was no rise in Cai2+. 3. Pre‐treatment of cells with noradrenaline or caffeine did not prevent the rise in Cai2+ on subsequent application of ATP. 4. The ATP‐activated rise in Cai2+ was voltage dependent as outward currents evoked by ATP at positive membrane potentials were not associated with a change in Cai2+. 5. At ‐‐60 mV, the rise in Cai2+ due to ATP application was dependent on the magnitude of the ATP current response, such that Cai2+ increased by about 0.5 nM/pC charge transferred through ATP‐gated channels. 6. The results suggest that ATP‐gated channels in these cells admit sufficient Ca2+ in a physiological Ca2+ gradient to significantly elevate Cai2+. About 10% of the ATP‐gated current may be carried by Ca2+ ions. Thus the ATP‐activated channels have a dual excitatory function: depolarization due to Na+ entry promotes action potential discharge and voltage‐gated Ca2+ entry, and also direct entry of Ca2+ through the ATP‐activated channels.
Neural correlates of horizontal vestibulo‐ocular reflex cancellation during rapid eye movements in the cat.
Authors: Berthoz A , Droulez J , Vidal P P , Yoshida K
Published: December 2014

1. The aim of the present study is to describe the behaviour of identified second‐order vestibular neurones in the alert cat during eye saccades. A selection of neurones which are involved in horizontal eye movements has been made. The activity has been compared with a selected sample of abducens motoneurones recorded in the same animals. 2. Alert head‐fixed cats were used for this study. Eye movements were recorded by the scleral search coil technique. Abducens motoneurones were identified by antidromic stimulation from the VIth nerve with chronically implanted electrodes. They were recorded extracellularly. 3. Second‐order vestibular neurones were identified by orthodromic stimulation from the vestibular organs. They were recorded intra‐axonally and injected with horseradish peroxidase after recording of their physiological characteristics. Their morphology was reconstructed from frozen sections. 4. All the recorded vestibular neurones showed various amounts of eye position sensitivity. The firing rate (F) ‐ horizontal eye position (H) characteristics are compared for abducens and vestibular neurones. The population average values are F = 33 + 4 H for motoneurones and F = 51 + 2.4 H for vestibular neurones. 5. All recorded vestibular neurones showed an increase of discharge rate during contralateral horizontal saccades and a strong decrease or pause during ipsilateral saccades. Firing rate ‐ horizontal eye velocity sensitivity has been calculated. 6. Results suggest a strong inhibitory input on vestibular neurones from the saccadic generator. This mechanism underlies the suppression of the vestibulo‐ocular reflex during saccades. Our results suggest that in the cat, for saccades of amplitude smaller than 20 deg, there is a variable degree of suppression which is provided by a projection of excitatory bursters (EBNs) on second‐order vestibular neurones through inhibitory type II neurones. 7. We also conclude from this study that the eye position sensitivity of vestibular second‐order neurones is in fact a motor signal indicating a motor error, i.e. the amount of head or eye movement which remains to be done in order to align gaze on target with the eyes centred in the orbit.
Inhibition of acid formation and stimulation of somatostatin release by cholecystokinin‐related peptides in rabbit gastric glands.
Authors: Bengtsson P , Lundqvist G , Nilsson G
Published: December 2014

1. The purpose of the present study was to investigate the role of somatostatin in the inhibition of acid production induced by caerulein and cholecystokinin (CCK) in isolated rabbit gastric glands. Acid production was estimated by the aminopyrine technique. 2. Exogenous somatostatin 14 and somatostatin 28 (10(‐7) M) reduced to a similar extent the aminopyrine uptake produced by 5 x 10(‐5) M‐histamine during the course of 40 min incubation. 3. Significant inhibition of histamine‐stimulated aminopyrine accumulation occurred at a somatostatin 14 concentration of 10(‐9) M. 4. Caerulein and CCK octapeptide (10(‐13)‐10(‐7) M) were found to release somatostatin from isolated gastric glands in a dose‐dependent manner. The dose‐response relationships for somatostatin release and inhibition of aminopyrine uptake were similar. Thus, the half‐maximal dose approximations for somatostatin release and inhibition of aminopyrine uptake were 0.5 and 1.4 x 10(‐9) M respectively for CCK octapeptide and 0.9 and 2.5 x 10(‐11) M for caerulein. Heptadecapeptide gastrin proved to be a very poor releaser of somatostatin in the system used. The CCK octapeptide‐induced somatostatin release was time dependent and the concentrations of somatostatin that accumulated in the incubation medium were similar to those of exogenous somatostatin that were needed to evoke inhibition. 5. The present results support the concept that cholecystokinin inhibits gastric acid secretion by releasing somatostatin from endocrine‐like cells in the gastric mucosa. It is suggested that cholecystokinin‐related peptides may play a physiological role in inhibiting gastric acid secretion. A similar role for gastrin is not supported by the present study.
Voltage dependence of Ia reciprocal inhibitory currents in cat spinal motoneurones.
Authors: Stuart G J , Redman S J
Published: December 2014

1. Inhibitory postsynaptic currents (IPSCs) were recorded in voltage clamped posterior biceps or semitendinosus motoneurones of the cat during reciprocal inhibition. 2. Population IPSCs, recorded following stimulation of the whole quadriceps muscle nerve, had an average time‐to‐peak of 0.51 +/‐ 0.02 ms (+/‐ S.E.M., n = 22) and decayed exponentially, with an average time constant of 0.99 +/‐ 0.04 ms (at 37 degrees C) at resting membrane potentials. 3. Unitary IPSCs, recorded following spike‐triggered averaging from an identified reciprocal inhibitory interneurone, had amplitudes of 120‐220 pA with an average time‐to‐peak of 0.40 +/‐ 0.06 ms (n = 5). The decay of these unitary currents was exponential, with an average time constant of 0.82 +/‐ 0.07 ms (at 37 degrees C) at resting membrane potentials. 4. The time course of IPSCs was unaffected by either alpha‐chloralose or pentobarbitone at concentrations necessary for deep anaesthesia. 5. The peak synaptic current varied linearly with the membrane potential over the range ‐90 to ‐30 mV, and had an average reversal potential of ‐80.7 +/‐ 1.5 mV (+/‐ S.E.M., n = 6) when measured using KCH3SO4‐filled electrodes. 6. The reversal potential for the IPSC was used to calculate [Cl‐]i. This was estimated to be 6.5 mM assuming that the inhibitory synaptic current was mediated purely by Cl‐ ions. 7. The rate at which synaptic currents decayed was exponentially dependent on the postsynaptic membrane potential, the decay time constant increasing e‐fold for a 91 mV depolarization. This result was independent of [Cl‐]i or of the magnitude of the synaptic conductance and was interpreted as a voltage dependence of the glycine channel open time. 8. The average unitary peak conductance was 9.1 +/‐ 1.7 nS (+/‐ S.E.M., n = 5), corresponding to the opening of approximately 200 glycine‐activated postsynaptic channels following neurotransmitter release from a single Ia reciprocal interneurone.
Transport of calcium across the dually perfused placenta of the rat.
Authors: Stulc J , Stulcová B , Svihovec J
Published: December 2014

1. A rat placenta was dually perfused in situ with modified Krebs fluid. Perfusion was carried out through the femoral artery on the maternal side and through the umbilical artery on the fetal side. 2. Transfer of 45Ca2+ and [3H]L‐glucose across the placenta was measured in the maternal‐fetal direction. The transcellular component of the maternal‐fetal transport of Ca2+, Jmf,tc, was estimated from transfer rates of the two tracers and from Ca2+ concentration in maternal perfusate, [Ca2+]m. 3. At [Ca2+]m of 1.1 mM (physiological concentration of Ca2+ in plasma) Jmf,tc was 92.4 +/‐ 13.7 nmol min‐1 (mean +/‐ S.D.), which is about 90% of the transport expected in an intact placenta. The permeability‐surface area product (PS) of the placenta to [3H]L‐glucose was 13.8 +/‐ 3.9 microliters min‐1, about 4 times higher than that expected in intact placenta. 4. Transport of 45Ca2+ changed rapidly when [Ca2+]m was varied. Kinetic constants of the transcellular transport of Ca2+ are the Michaelis constant, Km, = 0.45 mM and the maximum rate of transport, Vmax, = 116 nmol min‐1. It follows from this that at physiological levels of Ca2+, transport of Ca2+ to the fetus is relatively independent of changes in [Ca2+]m. 5. Strontium and barium (SrCl2 and BaCl2, 1 mM) decreased Jmf,tc; the response was prompt and reversible. Magnesium (2 mM) had no effect. Maternal‐fetal transport of 85Sr2+ and 133Ba2+ was decreased rapidly and reversibly by elevating [Ca2+]m from 0.35 to 2 mM. These observations suggest that Sr2+ and Ba2+ are transported across the placenta by the Ca2+ transport system. This means that the transport is not substrate specific. 6. Cadmium (1 mM‐CdCl2) decreased Jmf,tc irreversibly with some latency. The slowness of the response suggests a non‐competitive inhibition. Cadmium (0.02 mM‐CdCl2) was without effect on Jmf,tc. 7. A Ca2+ channel blocker, nifedipine (10 microM), administered to the maternal side had no effect on Jmf,tc.
Apical potassium channels in Amphiuma diluting segment: effect of barium.
Authors: Giebisch G , Hunter M , Kawahara K
Published: December 2014

1. Single potassium channels have been studied in the apical membrane of isolated diluting segment tubules of Amphiuma using the patch clamp technique in the cell‐attached mode. A kinetic analysis of the interaction of the channel with barium is presented. 2. The channel shows inward rectification, with an inward conductance of 29.2 pS and an outward conductance of 7.5 pS (cell attached, 100 mM‐KCl as pipette solution). 3. The channel is mildly voltage sensitive, the open probability of 0.8 at the resting membrane potential being reduced to 0.38 mV at a hyperpolarizing potential of 120 mV. The mean open time also decreased with hyperpolarization (from 51.3 to 11.6 ms at the above potentials). 4. Inclusion of barium in the pipette solution causes a concentration‐ and voltage‐dependent block of the channel. The open probability was reduced by 40 and 79% of control with 0.1 and 1 mM‐barium respectively (0 mV pipette potential). This inhibition increases to 70 and 95% at a pipette potential of 80 mV. 5. From the voltage dependence of the blockade by barium, it is estimated that barium ions block at a site one‐third of the way across the membrane. 6. Given the high open probability of the channel at resting membrane potentials and the density of the channels on the apical surface of the cells it is concluded that the channels can account for the apical potassium conductance of the diluting segment of Amphiuma.
The effect of loop diuretics on Cl‐ transport in smooth muscle of the guinea‐pig vas deferens and taenia from the caecum.
Authors: Aickin C C , Brading A F
Published: December 2014

1. The role of Na+, K+, Cl‐ co‐transport, identified in the previous paper (Aickin & Brading, 1990), has been characterized further by investigation of the effects of loop diuretics on Cl‐ movements in the smooth muscle cells of guinea‐pig vas deferens measured by 36Cl fluxes and Cl(‐)‐sensitive microelectrodes. Some flux experiments were also repeated in the taenia from the guinea‐pig caecum. 2. Frusemide (2 mM) reduced the steady‐state Cl‐ content, slowed 36Cl loss into Cl(‐)‐free solution and both slowed and reduced Cl‐ accumulation by Cl(‐)‐depleted cells of the vas deferens. When anion exchange was inhibited by the presence of DIDS, (4,4'‐diisothiocyanostilbene‐2,2'‐disulphonic acid), frusemide further slowed the loss of Cl‐ into Cl(‐)‐free solution, further reduced Cl‐ accumulation such that Cl‐ uptake amounted to a level consistent with a passive distribution and halted the rise in the intracellular Cl‐ activity (aiCl) at levels above about 10 mM. 3. Application of the higher‐affinity loop diuretics bumetanide and piretanide in vas deferns had no significant effect on 36Cl efflux into Cl(‐)‐free solution or on the initial rate of rise of aiCl but reduced the final level attained. In the presence of DIDS, however, both agents further slowed efflux into Cl(‐)‐free solution, and halted the rise in aiCl at levels above about 10 mM. Measurement of greatly slowed intracellular pH transients on removal and readdition of external Cl‐ (Clo‐) in the presence of frusemide suggests that the larger effects of this drug are mediated by inhibition of anion exchange as well as of co‐transport. 4. The relative potency of the loop diuretics, investigated in the presence of DIDS was: bumetanide greater than piretanide greater than frusemide. This sequence was found in both vas deferens, using direct measurement of aiCl, and taenia, using 36Cl uptake. 5. Comparison of data from the vas and taenia showed that 36Cl efflux into Cl(‐)‐free, HCO3(‐)‐free solution was about twice as fast in the taenia, and that bumetanide or piretanide reduced this efflux to about the same rate as that observed in the vas with or without the loop diuretic. DIDS caused a similar absolute reduction of efflux in both preparations. 6. Stimulation of 36Cl efflux on readdition, and inhibition on removal of Nao+ in the presence of DIDS, was much greater in the taenia than in vas and in both preparations was blocked by bumetanide or piretanide.(ABSTRACT TRUNCATED AT 400 WORDS)
Mechanism of receptor‐mediated modulation of the delayed outward potassium current in guinea‐pig ventricular myocytes.
Authors: Yazawa K , Kameyama M
Published: December 2014

1. Receptor‐mediated modulation of the delayed outward potassium current (IK) was investigated in guinea‐pig single ventricular cells by using whole‐cell voltage clamp and intracellular dialysis. 2. Isoprenaline increased IK in a dose‐dependent manner with a half‐maximum dose of 1.8 X 10(‐8) M. Isoprenaline (10(‐6) M) maximally increased IK by a factor of 2.85. This effect did not depend on the concentration of intracellular Ca2+ [( Ca2+]i). 3. External application of 10(‐5) M‐forskolin and internal application of 5 X 10(‐5) M‐cyclic AMP or 5 X 10(‐6) M of the catalytic subunit of cyclic AMP‐dependent protein kinase (PKA) also increased IK about 3‐fold. The effect of isoprenaline on IK was masked by previous application of cyclic AMP. 4. All the above phosphorylating agents increased the amplitude of IK without a significant change in the current kinetics. 5. In the presence of 10(‐5) M‐forskolin, an additional application of 10(‐8) M‐12‐O‐tetradecanoylphorbol‐13‐acetate, an activator of protein kinase C (PKC), produced a further increase in IK, suggesting that the active sites of PKA and PKC on the IK channel are different. 6. Acetylcholine (10(‐6) M) suppressed IK when the current was previously enhanced by 2 X 10(‐8) M‐isoprenaline, but had little effect in the absence of isoprenaline. 7. We conclude that beta‐adrenergic modulation of IK is mediated by cyclic AMP‐dependent phosphorylation but not by an increase in [Ca2+]i, that PKA and PKC enhance IK independently, and that acetylcholine antagonizes beta‐adrenergic stimulation of IK most probably by inhibiting adenylate cyclase.
Current‐clamp analysis of a time‐dependent rectification in rat optic nerve.
Authors: Eng D L , Gordon T R , Kocsis J D , Waxman S G
Published: December 2014

1. Rat optic nerves were studied using intra‐axonal and whole‐nerve recording techniques in a sucrose‐gap chamber. Constant‐current pulses were applied across the outer compartments of the chamber to achieve a current clamp. 2. The nerves displayed a prominent time‐dependent conductance increase elicited by a hyperpolarizing constant‐current pulse, as evidenced by a relaxation or 'sag' in membrane potential towards resting potential. The inward current began at about 80 ms and reached a steady level over the next 100‐200 ms. Its magnitude progressively increased with increasing levels of hyperpolarization. 3. The inward current elicited by hyperpolarization was reduced, but not abolished, when Na+ was reduced from the normal bath concentration of 151 mM to 0 mM. In Na(+)‐free solutions the bath K+ concentration, [K+]o, was varied between 0 and 5 mM; the inward current was greatest when [K+]o was 5 mM and was abolished when [K+]o was zero. 4. The inward current was not abolished by tetrodotoxin (TTX), tetraethylammonium (TEA) or 4‐aminopyridine (4‐AP) suggesting that conventional voltage‐dependent sodium and potassium channels do not underlie the time‐dependent conductance increase. Low concentrations of Cs+ completely blocked the inward current, and Ba2+ induced a partial block. External application of divalent cations (Cd2+ and Mg2+) did not block the inward current. These properties are similar to the inwardly rectifying conductance observed in a central nervous system neurone. 5. Stimulus‐response curves obtained during the hyperpolarization pulse, before and during the conductance increase, indicate that excitability is increased during the conductance increase. This along with the intra‐axonal recordings demonstrates that the origin of the increased conductance is axonal and not glial. 6. It is concluded that central nervous system myelinated fibres in rat optic nerve display a prominent time‐dependent conductance increase in response to hyperpolarization that depends on both Na+ and K+ and is blocked by Cs+. This conductance is similar to an inward rectifier described for a variety of neurone types. The increased axonal excitability observed during the conductance increase suggests that its functional role may be to maintain or stabilize axonal excitability during periods of intense action potential activity.
Facilitatory and inhibitory transmitters modulate spontaneous transmitter release at cultured Aplysia sensorimotor synapses.
Authors: Dale N , Kandel E R
Published: December 2014

1. The monoamine transmitter 5‐hydroxytryptamine (5‐HT) and the peptide Phe‐Met‐Arg‐Phe‐amide (FMRFa), which appear to contribute to presynaptic facilitation and inhibition of the sensorimotor synapse in the abdominal ganglion of Aplysia, can modulate the frequency of spontaneous transmitter release at synapses formed between dissociated Aplysia sensory neurones and motoneurones in vitro. 2. 5‐HT caused a decrease in the mean time interval between consecutive miniature EPSPs (mEPSPs), while FMRFa, applied either by itself or together with 5‐HT, caused an increase in the mean time interval between consecutive mEPSPs. 3. Depolarization of the presynaptic neurone caused a decrease in the mean time interval between consecutive mEPSPs. This modulation required external Ca2+. 4. 5‐HT and FMRFa were able to modulate spontaneous release when applied in saline solutions lacking Ca2+ and containing Ca2(+)‐chelating agents, suggesting that the modulation of spontaneous release by 5‐HT and FMRFa did not require a Ca2+ influx. Similarly, spontaneous release could still be modulated by 5‐HT and FMRFa in saline solutions containing 1 mM‐Cd2+, which blocked both the voltage‐gated Ca2+ channels and the evoked transmitter release. 5. To prevent a rise in intracellular Ca2+, we buffered the concentration of Ca2+ in the presynaptic terminals by injecting into the sensory neurone the Ca2+ chelator 1,2‐bis(o‐aminophenoxy)ethane‐N,N,N',N'‐tetraacetic acid (BAPTA). The injection of BAPTA blocked evoked transmitter release, suggesting that it acted as an effective buffer of Ca2+ in the terminals. However, spontaneous release could still be observed and was still modulated by 5‐HT and FMRFa. This suggests that the modulation of spontaneous release does not require an elevation of intracellular Ca2+. 6. We propose that 5‐HT and FMRFa can modulate the rate of spontaneous release directly by mechanisms that do not require changes in the intracellular concentration of Ca2+. These mechanisms might contribute an additional component to the presynaptic inhibition and facilitation of evoked transmitter release.
Spatial organization of the bipolar cell's receptive field in the retina of the tiger salamander.
Authors: Hare W A , Owen W G
Published: December 2014

1. The spatial properties of rods, horizontal cells and bipolar cells were studied by intracellular recording in the isolated, perfused retina of the tiger salamander, Ambystoma tigrinum. Low stimulus intensities were used in order to keep cell responses close to, or within, their linear intensity/response range. 2. Spatial properties of bipolar cell receptive fields, measured while perfusing with normal Ringer solution, were compared with those measured during exposure to agents that eliminated the bipolar cells' receptive field surround (RFS). In this way, the spatial properties of the receptive field centre (RFC) and those of the RFS could be characterized independently. 3. To a good approximation, the contribution to the horizontal cell's response of unit area of its receptive field declined exponentially with distance from the centre of the receptive field. The (apparent) length constant describing this decay was 200 microns. The one‐dimensional length constant of the horizontal cell syncytium was thus 248 microns. The variation of response amplitude with the radius of a centred circular stimulus was consistent with this finding. 4. This was true also of the RFCs of bipolar cells. The one‐dimensional length constant of the RFC of off‐centre bipolar cells averaged 124 microns. That of the RFC of on‐centre cells averaged 62 microns though values were more variable, the RFCs of some on‐centre cells being comparable to those of off‐centre cells. These values were independent of the class of photoreceptor driving the bipolar cell. 5. The large size of the RFCs of off‐centre cells and many on‐centre cells cannot by explained by light scatter within the retina or by voltage spread within the rod syncytium. We proposed that off‐centre cells are tightly coupled in a syncytium. On‐centre cells, on average, are less tightly coupled. 6. The spatial properties of the bipolar cell's RFS were consistent with the notion that the RFS represents a convolution of the horizontal cell's receptive field and the bipolar cell's RFC. 7. The spatial properties of bipolar cell receptive fields were reconstructed from the measured properties of their RFCs and the measured properties of horizontal cell receptive fields. Under the conditions of our experiments, the bipolar cell's response could be described by a linear difference between a component generated by the RFC and a component generated by the RFS. 8. The spatial filtering characteristics of the bipolar cells were calculated from our data.(ABSTRACT TRUNCATED AT 400 WORDS)
Potassium currents in inner hair cells isolated from the guinea‐pig cochlea.
Authors: Kros C J , Crawford A C
Published: December 2014

1. Inner hair cells were mechanically isolated from the apical, low‐frequency region of the guinea‐pig cochlea and maintained by superfusion with tissue‐culture medium. Membrane currents were studied under voltage clamp, using the whole‐cell recording mode of the patch‐clamp technique. 2. The cells were studied mostly at 35‐38 degrees C to obtain realistic kinetics of the currents, relevant to the functioning of these cells in vivo. 3. Isolated inner hair cells had resting potentials of about ‐65 mV. Depolarizing voltage steps from a holding potential of about ‐80 mV resulted in large time‐ and voltage‐dependent outward currents. Hyperpolarizing voltage steps from the same holding potential only showed a small leakage conductance of 0.5‐2.5 nS. 4. On repolarization to different membrane potentials, the tail currents reversed around ‐75 mV. This indicates that the outward currents were mainly carried by potassium ions. 5. Pharmacological dissection of the currents provided evidence for two different potassium conductances. The largest conductance had extremely fast kinetics. Its principal time constant of activation was about 0.15‐0.35 ms, the faster values being obtained for larger depolarizations. This fast potassium conductance was blocked by 25 mM‐tetraethylammonium chloride in the bath. 6. A smaller, slow potassium conductance, with principal time constants of activation of 2‐10 ms (speeding up with depolarization), was blocked by 10‐15 mM‐4‐aminopyridine in the patch pipette. 7. Both potassium conductances were activated over the membrane potential range of about ‐60 to ‐20 mV. This is approximately the same as the range of the receptor potential measured in vivo. Therefore these conductances should influence the properties of the receptor potential in inner hair cells. 8. Current injection experiments showed two main effects of the potassium conductances: (a) a non‐linearity in the voltage‐current relationships; (b) a strongly damped oscillation of the membrane potential in response to a large step of outward current. This oscillatory behaviour is caused by the fast potassium conductance.
Background and bleaching adaptation in luminosity type horizontal cells in the isolated turtle retina.
Authors: Normann R A , Perlman I
Published: December 2014

1. The effects of background illumination and bleached photopigment on luminosity type horizontal cells were studied in the isolated turtle retina. 2. Background illumination, which produced less than 60% bleaching, hyperpolarized and desensitized the horizontal cells to a degree which depended upon the background intensity. The desensitization of horizontal cells by these backgrounds is described by a Weber‐Fechner type relationship. This desensitization primarily reflects the activation of a ‘gain reduction’ mechanism and cannot be accounted for by ‘response compression’. 3. Following the termination of these backgrounds, horizontal cell sensitivity partially recovered but did not return to the pre‐background, dark‐adapted level. This desensitization was attributed to the presence of bleached photoproducts which were produced by the background exposure. 4. Application of very bright backgrounds caused the horizontal cells to initially hyperpolarize, and then to gradually depolarize towards the dark‐adapted level along an exponential time course which appeared to reflect the decreased quantal catching associated with very high levels of photopigment bleaching. 5. From the time constant of the exponential decay of horizontal cell potential during the bright background illumination, the photosensitivity to bleaching of the cone photopigment was determined to be 4.5 x 10(7) effective quanta (633 nm) microns‐2. 6. After termination of bright backgrounds which bleached more than 99% of the cone photopigment, the horizontal cell sensitivity increased linearly with time and after 25 min reached a level which was about 15% of the pre‐background sensitivity. 7. Bleached photopigment reduces light sensitivity via at least two different mechanisms. For moderate degrees of bleaching (less than 95%), the presence of bleached photoproducts plays the major role in sensitivity control, producing a desensitization which is logarithmically related to the fraction of bleached pigment. During extensive bleaching (greater than 99%), the contribution of reduced quantal catching to sensitivity control becomes apparent and produces an additional loss in sensitivity which is linearly related to the fraction of unbleached pigment present.
Reversal and inhibition of cholera toxin‐induced secretion in isolated rabbit ileum.
Authors: Falk G , Freeman M , Marshall A T , Prenton E , Shiells R A , Slack I
Published: December 2014

1. Cholera toxin (1 microgram/ml) abolished net fluid absorption by everted sacs of rabbit ileum, leading to net fluid secretion. This action occurred via the toxin‐catalysed ADP ribosylation of the stimulatory GTP‐binding protein Gs which is linked to adenylate cyclase. Nicotinamide (10 mM), a reaction product of ADP ribosylation, reversed cholera toxin‐induced secretion, restoring absorption. Lower concentrations of nicotinamide induced partial reversal. 2. Nicotinamide (1 mM) blocked the secretory action of cholera toxin applied to ileal sacs. This inhibitory action was more effective in the presence of methionine (1 mM). 3. Other inhibitors of ADP ribosylation, benzamide and adenine, blocked the secretory action of cholera toxin. Hypoxanthine, an analogue and metabolite of adenine, was similarly effective. 4. Nicotinamide was not, however, effective in blocking or reversing the secretory action of theophylline (10 mM) or of heat‐stable E. coli enterotoxin STa. This indicates that nicotinamide has a highly specific action against ADP ribosylating toxins. 5. It is proposed that nicotinamide reverses the secretory action of cholera toxin by reversing ADP ribosylation, simply by the law of mass action. This counters the established idea that the effects of cholera and other ADP‐ribosylating toxins are irreversible under physiological conditions.
Anionic mechanisms of zinc uptake across the human red cell membrane.
Authors: Kalfakakou V , Simons T J
Published: December 2014

1. Zinc is taken up into human red cells by two mechanisms that depend upon the presence of anions. One of these requires bicarbonate ions, is inhibited by 4,4'‐diisothiocyanatostilbene‐2,2'‐disulphonic acid (DIDS) and appears to be catalysed by the anion exchanger. The second occurs in the presence of thiocyanate or salicylate ions and may represent transport of a neutral complex with Zn2+. 2. The initial rate of Zn2+ uptake via the anion exchanger is 64 +/‐ 13 mumol (10(13) cells x h)‐1 microM‐1 external Zn2+, in the presence of 5 mM‐bicarbonate at pH 7.4 and 37 degrees C (+/‐ S.D.). This is about 1/250 of the corresponding rate of Pb2+ uptake by the anion exchanger. 3. The variation of transport with Zn2+ concentration, HCO3‐ concentration and pH suggests that the transported species may be ZnCO3Cl‐ or Zn(HCO3)Cl.OH‐. 4. Zinc efflux could not be observed by either of the above routes. This observation suggests that the intracellular free Zn2+ concentration is below 3 nM.