bluuebunny/crossref_metadata_2025 huggingface dataset:
Lesions in the upper lateral pons abolish the hypoxic depression of breathing in unanaesthetized fetal lambs in utero.
Authors: Gluckman P D , Johnston B M
Published: December 2014

1. The effects of stereotaxically placed lesions made throughout the mid‐brain and upper pons were studied in chronically instrumented fetal lambs from 120 days gestation, after recovery in utero. 2. Isocapnic hypoxia caused an increase in the rate and depth of breathing movements in fetuses in which bilateral lesions encompassed the upper lateral pons in the region of and slightly rostral to the principal sensory and motor nuclei of the trigeminal nerve. 3. Fetal lambs with lesions which did not bilaterally encompass the upper lateral pons showed the normal fetal depressive response to hypoxia. 4. None of the lesions induced permanent continuous breathing as previously described in mid‐brain transected fetuses, although periods of continuous breathing lasting several hours were seen at times in some fetuses with lesions in the upper lateral pons. 5. It is concluded that an area in the lateral pons close to areas with well known involvement in respiratory control is involved in the hypoxic depression of breathing in the fetal lamb.
Calcium transport across the isolated dually perfused human placental lobule.
Authors: Abramovich D R , Dacke C G , Elcock C , Page K R
Published: December 2014

1. Movements of 45Ca and 3H2O in maternal to fetal (M‐‐‐‐F) and fetal to maternal (F‐‐‐‐M) directions across the dually perfused isolated human placental lobule were measured under steady‐state conditions. 2. M‐‐‐‐F values of the clearances (CR) and extractions (ER) of 45Ca relative to 3H2O were 0.371 +/‐ 0.056 and 0.492 +/‐ 0.086 (mean +/‐ S.E. of mean) respectively. The corresponding values for F‐‐‐‐M movements were 0.277 +/‐ 0.017 and 0.251 +/‐ 0.010 respectively. The F‐‐‐‐M perfusion flow ratio (QF/QM) was 0.34 +/‐ 0.01 throughout. Comparison with previously published data indicated a significant degree of membrane limitation to Ca transfers. 3. There was evidence of a mismatch between tissues receiving a fetal and those receiving a maternal perfusion. 4. The relative extraction ER was markedly and reversibly enhanced when perfusate total Ca was reduced from 2.4 to 0.1 mM. The effect was present in both M‐‐‐‐F and F‐‐‐‐M transfers and provided evidence for carrier‐mediated uptake of Ca on both aspects of the placental barrier. Small and transient decreases in the relative clearance CR were observed on changing from 2.4 to 0.1 mM‐Ca in M‐‐‐‐F and to a lesser extent F‐‐‐‐M transfers while transient increases were seen on changing from 0.1 back to 2.4 mM‐Ca. 5. Measurement of net changes in Ca levels in closed‐circuit studies indicated a significant release of both ionized (Ca2+) and total (CaT) Ca into the fetal perfusate at total Ringer solution concentrations of 1.4, 1.9 and 2.4 mM‐Ca. Release of Ca into the maternal circuit was also observed using 1.4 mM‐Ca Ringer solution but when 1.9 and 2.4 mM‐Ca Ringer solution was used a net uptake occurred. 6. These findings strongly suggest that mechanisms by which Ca is transferred from M‐‐‐‐F circulations in vivo are at least partly preserved in the in vitro human placental preparation. They indicate that this preparation is suitable for the study of these mechanisms and their regulation by hormonal and other factors.
Chronic block of the cervical trunk increases synaptic efficacy in the superior and stellate ganglia of the guinea‐pig.
Authors: Gallego R , Geijo E
Published: December 2014

1. The effects of chronic conduction block with tetrodotoxin (TTX) of the cervical sympathetic trunk on synapses in the superior and stellate ganglia were examined in vitro with intracellular recording techniques. 2. The mean maximum amplitude of excitatory post‐synaptic potentials (e.p.s.p.s) evoked in superior cervical ganglion neurones by stimulation of the cervical sympathetic trunk was increased significantly after 2 or 4 days of block. The electrical properties of the ganglion cells were not appreciably changed by the period of inactivity. 3. Chronic conduction block for 4 days also resulted in a significant increase in the amplitude of the e.p.s.p.s. evoked in stellate ganglion cells by active collaterals of the blocked fibres. 4. The number of steps in the synaptic response elicited in individual stellate ganglion neurones by graded stimulation of the ansa subclavia and the subclavian trunk (which join to form the cervical sympathetic trunk) was increased after 4 days of conduction block. 5. These results show that elimination of impulse activity in the cervical sympathetic trunk increased synaptic efficacy at the disused synapses in the superior cervical ganglion and at the active synapses in the stellate ganglion. In the latter case, collaterals of the blocked fibres apparently formed new synaptic connexions on stellate ganglion cells.
Sodium current kinetics in cat atrial myocytes.
Authors: Follmer C H , ten Eick R E , Yeh J Z
Published: December 2014

1. Na+ current kinetics were studied in isolated atrial myocytes from the adult cat using the single suction‐pipette voltage‐clamp technique. 2. Current‐voltage and conductance‐voltage relationships were similar to those described in other cardiac myocyte preparations. 3. Analysis of Na+ current decay using single‐pulse, double‐pulse and tail current measurements were in agreement and demonstrate a second‐order process of current decay. 4. Voltage dependence of steady‐state inactivation curves was not symmetrical, having an inflexion at about ‐90 mV. These results suggest more than a single inactivation process for Na+ channel in the negative potential region. 5. Recovery of Na+ current from inactivation had a sigmoid time course: an initial slow component (delay) followed by a fast and then a second slow component. Increasing the pre‐pulse duration slowed the time course of recovery. 6. Taken together, the results were consistent with the presence of multiple inactivated states for the atrial myocyte Na+ channel.
Blockade of prostaglandin E1 hyperthermia by sodium salicylate given into the ventral septal area of the rat brain.
Authors: Alexander S J , Cooper K E , Veale W L
Published: December 2014

1. Sodium salicylate (30.0 micrograms microliter‐1) or artificial cerebrospinal fluid (ACSF) was infused bilaterally into the ventral septal area (v.s.a.) of the unrestrained rat for 1 h before and 1 h after the injection of prostaglandin E1 at a concentration of 20.0 ng microliter‐1 into a lateral cerebral ventricle. 2. During control (ACSF) infusions, 200.0 ng of prostaglandin E1 evoked a hyperthermic response (0.95 +/‐ 0.16 degrees C). During sodium salicylate infusions, the prostaglandin E1‐evoked hyperthermia was significantly reduced (P less than 0.025) to 0.31 +/‐ 0.16 degrees C. 3. The fever index (degrees C h for 1.0 h) during the infusion of sodium salicylate was reduced 66% below that of control infusions (P less than 0.01). 4. These data indicate that sodium salicylate infused in the v.s.a. of rats can antagonize a prostaglandin E‐evoked hyperthermia. This suggests that there may be an additional mechanism of action for sodium salicylate antipyresis other than inhibition of prostaglandin E synthesis.
Significance of active ion transport in transalveolar water absorption: a study on isolated rat lung.
Authors: Basset G , Crone C , Saumon G
Published: December 2014

1. Experiments were performed on isolated rat lungs perfused with Ringer solutions containing red cells. The goal was to clarify the role of active transport of Na+ for the absorption of fluid across the alveolar membrane, and to characterize active and passive pathways. 2. Partially degassed lungs were filled with 5 ml of an isotonic Ringer solution containing 125I‐labelled albumin in order to calculate the fluid movement, and 22Na+ or 36Cl‐ for measurement of ion fluxes. Passive non‐electrolyte permeability was determined in all experiments using [3H]mannitol. 3. The average rate of fluid absorption in phosphate‐buffered instillates was 134 nl/s (S.E., 18.5; n = 14). With ouabain (10(‐4) M) in the perfusate the fluid absorption rate fell to 57 nl/s (S.E., 8.2; n = 18). Amiloride (10(‐3)‐10(‐4) M) in the instillate reduced the absorption to 75 nl/s (S.E., 8.6; n = 16). These results show that fluid absorption depends on transcellular transport of Na+ and that alveolar epithelial cells have a Na+ entry system in the luminal membrane and a Na+‐K+ pump in the abluminal membrane. 4. The transcellular ion transport operates in parallel with a paracellular, passive leak that allows mannitol to pass with a permeability surface area product of 1.2 X 10(‐4) ml/s, corresponding to a permeability coefficient of 2.4 X 10(‐8) cm/s, assuming an alveolar surface area of 5000 cm2. 5. The passive fluxes of Na+ were 9.4 pmol/(cm2s) (S.E., 1.3; n = 25) in the direction from alveoli to perfusate and 8.0 pmol/(cm2s) (S.E., 0.86; n = 6) from perfusate to plasma. The passive fluxes of Cl‐ in the two directions were not significantly different either. Thus the transalveolar electrical potential difference is too small to affect ion movements measurably. 6. The passive permeability to Na+ was 6.7 X 10(‐8) cm/s and to Cl‐ was 10.2 X 10(‐8) cm/s (alveolar surface area assumed to be 5000 cm2). The ratio of the permeabilities is close to the ratio of the diffusion coefficients in free solution, suggesting a neutral or weakly charged paracellular channel. 7. We conclude that the alveolar epithelium performs solute‐coupled fluid transport from alveoli to plasma, and that it shows many features that are common to other fluid‐transporting epithelia; with an approximate surface area of 100 m2 in humans it constitutes one of the largest epithelial surfaces in the body.(ABSTRACT TRUNCATED AT 400 WORDS)
Effect of prolonged depolarizations on twitch tension and intracellular sodium activity in sheep cardiac Purkinje fibres.
Authors: Brill D M , Fozzard H A , Makielski J C , Wasserstrom J A
Published: December 2014

1. Twitch tension and intracellular Na+ activity (aiNa) were measured in voltage‐clamped sheep cardiac Purkinje fibres. aiNa was measured using Na+‐sensitive micro‐electrodes filled with the liquid ion exchange resin. ETH 227. The stimulus for contraction was a constant 200 ms depolarizing pulse to 0 mV from a holding potential of ‐80 mV delivered at 0.25 Hz. Prolonged test pulses for 1.8 s (post‐pulses) were applied at the end of the stimulus pulse. The effects of post‐pulses on twitch tension and aiNa were examined. 2. Post‐pulses in the range of ‐40 mV reduced twitch tension below control force produced without post‐pulse. Progressively more positive post‐pulses to levels above 0 mV profoundly increased twitch tension, with a greater than 400% rise in tension at +50 to +60 mV compared to control tension. aiNa declined at positive post‐pulse potentials by more than 2 mM at +30 to +40 mV. 3. Tetrodotoxin (100 microM) did not affect the post‐pulse voltage‐tension or voltage‐aiNa relation. Ca2+ channel modulation with nitrendipine (1 microM) similarly did not alter the post‐pulse voltage‐tension relation. 4. Removal of extracellular Na+ eliminated the nadir in tension at post‐pulses to ‐40 mV and the augmentation of tension at post‐pulses above 0 mV. 5. We interpret these findings as evidence of voltage‐sensitive Na‐Ca exchange promoting net Ca2+ influx and net Na+ efflux during positive post‐pulses. The unusual shape of the post‐pulse voltage‐tension relation curve can be accounted for by a charged‐carrier model of electrogenic Na‐Ca exchange. The inverse relation between aiNa and twitch tension probably reflects the combined effects of reduced aiNa leak and changes in Na+ and Ca2+ flux via voltage‐sensitive Na‐Ca exchange.
The role of the sarcoplasmic reticulum in the response of ferret and rat heart muscle to acidosis.
Authors: Orchard C H
Published: December 2014

1. The photoprotein aequorin was micro‐injected into papillary muscles from the right ventricle of ferrets and rats. Tension and aequorin light (a function of intracellular [Ca2+]) were monitored. 2. In stimulated ferret papillary muscles, increasing the [CO2] of the bicarbonate‐buffered superfusate from 5% (pH 7.35) to 20% (pH 6.8) led to a rapid decrease of developed tension, with no significant change in the size of the intracellular Ca2+ transient which accompanies contraction. There was then a small brief recovery of tension which was accompanied by a large brief increase in the size of the Ca2+ transient. Tension then declined again before recovering more slowly, with no significant change in the size of the Ca2+ transient. 3. The time course of the Ca2+ transient was prolonged on exposure to the acid solution, but shortened on continued exposure to the acid solution. Relaxation of twitch tension became faster on exposure to the acid solution, but slowed again on continued exposure to the acid solution. 4. In the presence of 10 mM‐caffeine the size of the Ca2+ transient increased during the initial decline of developed tension, the short‐lived recovery of tension was abolished, and the Ca2+ transient became smaller during the slower recovery of developed tension. 2 microM‐ryanodine had similar effects on developed tension. 5. Addition of 10 mM‐lactic acid to the superfusate produced changes similar to those described in 2 and 3 above. 6. An intracellular acidosis, produced by the addition and subsequent withdrawal of 20 mM‐NH4Cl from the superfusate also caused changes similar to those described above. In the presence of caffeine, withdrawal of NH4Cl produced changes similar to those described in 4 above. 7. In unstimulated ferret papillary muscles, increasing superfusate [CO2] produced an increase of aequorin light when the bathing [Ca2+] was increased or in the presence of ouabain (10 microM). This increase was not inhibited by verapamil (5 microM), carbonyl cyanide p‐trifluoromethoxyphenylhydrazone (1 microM) and oligomycin (2.5 microM), but was reduced by ryanodine (2 microM). 8. Rat papillary muscles showed responses which were quantitatively different from those observed in ferret papillary muscles: the initial recovery of tension developed more slowly, and sarcoplasmic reticulum (s.r.) inhibitors had a greater inhibitory effect on the recovery of tension. 9. It is concluded that the early decline of developed tension observed during acidosis is due to a decrease in Ca2+ release by the s.r. and a decrease in Ca2+ binding by the myofilaments.(ABSTRACT TRUNCATED AT 400 WORDS)
Endogenous bursting by rat supraoptic neuroendocrine cells is calcium dependent.
Authors: Andrew R D
Published: December 2014

1. Phasic bursting by magnocellular neuroendocrine cells (m.n.c.s) in vivo causes increased vasopressin release from axon terminals in the neurohypophysis. In the supraoptic nucleus of the coronal hypothalamic slice thirty‐two of sixty‐five m.n.c.s recorded intracellularly displayed repetitive bursting, either spontaneously or during a low level of tonic current injection. 2. Of the thirty‐two repetitive bursters, twenty‐four received no apparent patterned synaptic input and the phasic burst behaviour was voltage dependent. The evidence for these cells being bursting pace‐makers and the underlying mechanism driving bursting were further investigated. 3. Phasic bursting by m.n.c.s is usually contingent upon two depolarizing events: a slow depolarization (s.d.) between bursts that brings the membrane potential to burst threshold, and the spike depolarizing after‐potential (d.a.p.). One or several d.a.p.s can initiate a burst by summing to form a plateau potential which sustains firing. 4. Of eight phasic cells exposed to tetrodotoxin (TTX) and tonically depolarized with current injection, two cells retained the phasic burst pattern and underlying plateau potentials. Of the remaining six cells in TTX, three of four cells tested regained phasic firing with plateau potentials following the addition of Sr2+, a Ca2+ agonist. Evoked post‐synaptic potentials were demonstrably blocked throughout TTX exposure, firmly establishing that some m.n.c.s are bursting pace‐makers. 5. The s.d., d.a.p. and plateau potential were retained in TTX or low‐Na+ saline, augmented in Sr2+ and blocked in low‐Ca2+ saline. All three events were activated at membrane potentials depolarized from ‐70 mV but steadily inactivated with increasing hyperpolarization to ‐90 mV. The s.d. and d.a.p. apparently represented partial activation of the same process that drives a burst, the plateau potential. 6. Hyperpolarizing pulses of constant current revealed an apparent decrease in cell conductance underlying the s.d., d.a.p. and plateau potential which was not due to membrane rectification. The plateau potential was reduced in low Na+ and eliminated in low Ca2+. However, it remained relatively unaffected by altering the external K+ concentration and it did not reverse below ‐90 mV, suggesting a less important role for K+ movement relative to Ca2+ or Na+. A hyperpolarizing pulse during the s.d., d.a.p. or plateau potential probably momentarily inactivated inward Ca2+ current, causing the apparent conductance decrease.(ABSTRACT TRUNCATED AT 400 WORDS)
Isoperiodic bursting by magnocellular neuroendocrine cells in the rat hypothalamic slice.
Authors: Andrew R D
Published: December 2014

1. Recruitment of magnocellular neuroendocrine cells (m.n.c.s) to a repetitive burst pattern (phasic firing) is associated with increased vasopressin secretion from neurohypophysial terminals in the intact animal. Based on invertebrate studies, bursts of action potentials can arise in two distinct ways: as an intrinsic property of the recorded cell or as an emergent property of synaptic interactions. 2. The majority of phasic m.n.c.s in the hypothalamic slice preparation display an endogenous pace‐maker mechanism underlying bursting. It is voltage dependent and varies considerably in periodicity and time course as described in the accompanying paper (Andrew, 1987). 3. In contrast to this intrinsic mechanism, the present study examined if cells might be driven by periodic synaptic input. Intracellular recordings from six of thirty‐two phasic m.n.c.s in the supraoptic nucleus revealed an isoperiodic oscillation of the membrane potential, where each depolarizing phase could support a burst. 4. The oscillation had a smooth trajectory and fixed period (range, 5‐17 s). The oscillatory frequency was not voltage dependent, i.e. periodicity was unaffected by steady current injection through the recording electrode. 5. The frequency and amplitude of the oscillation remained unaltered by action potential firing. The isoperiodic oscillation could abate spontaneously, leaving intact the endogenous ability to fire a triggered burst driven by an underlying plateau potential. 6. Perfusion with either 10 mM‐Mg2+‐0.05 mM‐Ca2+ or 0.5‐2.0 microM‐tetrodotoxin blocked both the oscillation and evoked post‐synaptic potentials, indicating that the oscillation was synaptically generated. Given that both treatments could also block the intrinsic burst process and that the oscillation could spontaneously abate, the synaptic nature of the oscillation remains a tentative but reasonable conclusion. 7. In total, the evidence suggests that the isoperiodic oscillation has a synaptic origin independent of intrinsic mechanisms. It probably results from synaptic input generated within the slice but the source is not yet identified. This input could support phasic bursting in those m.n.c.s lacking a pace‐maker ability and so promote the release of vasopressin in the intact animal.
Phosphate transport in brush‐border membranes from control and rachitic pig kidney and small intestine.
Authors: Brandis M , Harmeyer J , Kaune R , Mohrmann M , Murer H , Zimolo Z
Published: December 2014

1. Na‐Pi co‐transport was analysed using renal cortical and small intestinal brush‐border membrane vesicles which were isolated from control (normal, heterozygotes) and rachitic piglets (homozygotes). 2. A kinetic analysis of Na‐dependent initial linear uptake of Pi was performed using vesicles obtained from control animals. The results suggest similar kinetic properties for the renal and small intestinal co‐transport system. (i) A sigmoidal dependence on Na concentration of Pi uptake suggests the involvement of more than one Na ion in the co‐transport. (ii) Increasing Na concentration leads to an increase in the apparent affinity of the transport system for Pi and has minimal effect on the apparent Vmax (maximum velocity of uptake). (iii) Increasing pH leads to an increase in Pi transport rate. 3. The kinetic characteristics of the Na‐Pi co‐transport system in vesicles obtained from rachitic animals were similar to those in controls. The apparent Vmax, but not the apparent Km (Michaelis constant) for Na and Pi, is reduced in intestinal and renal brush‐border membranes isolated from rachitic animals as compared to control animals. Injection of vitamin D3, three days prior to killing of rachitic litter‐mates, increased the Na‐Pi uptake rate in the brush‐border membrane vesicles isolated from these piglets. 4. It is concluded that intestinal and renal brush‐border membranes from piglets contain a similar Na‐Pi co‐transport system and that in vitamin‐D‐dependent rickets the number of operating transport units is reduced in both membranes.
The ventral and dorsal lateral geniculate nucleus of the rat: intracellular recordings in vitro.
Authors: Crunelli V , Kelly J S , Leresche N , Pirchio M
Published: December 2014

1. The membrane properties and the electrotonic structure of neurones in the ventral and dorsal lateral geniculate nucleus (l.g.n.) of the rat were studied using an in vitro slice preparation. 2. Following electrophysiological characterization, horseradish peroxidase (HRP) was injected intrasomatically and the morphological features of impaled cells were characteristic of principal neurones of the rat ventral and dorsal l.g.n. 3. Neurones in the ventral l.g.n. had a higher input resistance but similar membrane time constants (tau o) and resting potentials than cells in the dorsal l.g.n. 4. Using a simple neuronal model, the electrotonic length (L) and the dendritic to somatic conductance ratio (rho) were calculated and found to be similar for cells in both divisions of the l.g.n. The mean value of L (0.7) and rho (1.5) suggest that both groups of neurones are electrotonically compact. 5. The width and after‐hyperpolarization of directly evoked action potentials, but not their threshold or their amplitude, were different between cells of the ventral and dorsal l.g.n. 6. At potentials more negative than ‐55 mV, a slow rising and falling potential could be evoked in each neurone (n = 310) of the dorsal l.g.n. but only in three cells of the ventral l.g.n. (n = 94). The electrophysiological and pharmacological properties of this potential were identical with those of the low‐threshold Ca2+‐dependent potential observed in other thalamic nuclei. 7. These results indicate that some of the passive and active membrane properties of ventral and dorsal l.g.n. neurones are different. The implications of these findings for the control of the integrative capability and the response of l.g.n. neurones to visual stimulation are discussed.
On the excitatory post‐synaptic potential evoked by stimulation of the optic tract in the rat lateral geniculate nucleus.
Authors: Crunelli V , Kelly J S , Leresche N , Pirchio M
Published: December 2014

1. The electrophysiological and pharmacological properties of the excitatory post‐synaptic potentials (e.p.s.p.) evoked by electrical stimulation of the optic tract were studied in projection neurones of the ventral and dorsal lateral geniculate nucleus (l.g.n.) of the rat in vitro. 2. No difference was found in the rise time of e.p.s.p.s. recorded in the dorsal and ventral l.g.n. and in their threshold for action potentials. At membrane potentials more negative than ‐60 mV, e.p.s.p.s. in the dorsal l.g.n. were always followed by a Ca2+‐dependent potential. Its amplitude could easily reach threshold for generating an action potential and thus evoke firing from an e.p.s.p. that was subthreshold at resting potential. No Ca2+ potential was observed to follow e.p.s.p.s. recorded in the ventral l.g.n. 3. At resting potential the excitability of dorsal and ventral cells was unaffected following an initial shock to the optic tract. However, in dorsal neurones, at potentials more negative than ‐60 mV, the presence of Ca2+ potentials evoked by the e.p.s.p.s. resulted in a period of decreased excitability. 4. Using intrasomatic injection of Cs+ the reversal potential (E) of the e.p.s.p. and of the depolarization produced by glutamate could be measured in the same l.g.n. neurone. They were: Eepsp, ‐0.9 mV; and Eglut, ‐3.9 mV. 5. gamma‐D‐glutamylglycine (DGG), an excitatory amino acid antagonist, reversibly inhibited the e.p.s.p. and depolarization produced by quisqualate and glutamate by a competitive action. The concentration of DGG that produced 50% inhibition (IC50) was 2.7 mM. 6. D‐2‐amino‐5‐phosphonovalerate (APV), the potent and selective N‐methyl‐D‐aspartate (NMDA) antagonist, had no effect on the e.p.s.p. both in the presence and absence of Mg2+. The isomers of 2‐amino‐4‐phosphonobutyrate (APB) were inactive or had a non‐specific action on the e.p.s.p. 7. No difference could be detected in either the reversal potential or the action of the antagonists between neurones of the dorsal and the ventral l.g.n. 8. These results suggest that Ca2+‐dependent potentials play an important role in modulating synaptic efficacy in principal neurones of the dorsal l.g.n. The quisqualate/kainate nature of the optic nerve receptors and the similarity of Eepsp and Eglut constitute strong support in favour of a glutamate‐like substance as the transmitter of the optic nerve.
Complex spikes in Purkinje cells in the lateral vermis (b zone) of the cat cerebellum during locomotion.
Authors: Andersson G , Armstrong D M
Published: December 2014

1. Complex spikes (c.s.s) due to climbing fibre input were recorded from forty‐one Purkinje cells in the lateral part of the vermis (i.e. the b zone) of lobule V of the cerebellum in cats walking on a moving belt or a horizontal ladder. Most cells were near the tips of the folia making up the lobule and some were shown by antidromic invasion to project to the ipsilateral lateral vestibular nucleus. In all cells c.s.s. could be evoked through mechanical stimuli delivered manually to the neck and/or trunk and/or the limb girdles and/or the proximal parts of the limbs. 2. During walking c.s.s. occurred at rates which ranged in different cells from 0.8 to 2.55/s (i.e. ca. 0.8 to 2/step). When activity was averaged across many successive steps the probability of c.s. occurrence was never completely constant throughout the step cycle, but no tendency was detected for c.s.s to recur at any precisely fixed time during the cycle. 3. When ladder locomotion was perturbed because a rung underwent an unexpected 2 cm descent when stepped on, some cells generated a c.s. at short latency in a proportion of trials. Such responses were well time‐locked to the onset of rung movement but not to its cessation (which they often preceded). 4. For perturbations of either forelimb the earliest displacement‐related c.s. occurred in different cells between 40 and 64 ms after the onset of rung movement. In different cells c.s.s occurred in from one out of five to three out of four perturbed steps (mean ca. two out of five steps). Eight out of seventeen cells responded to perturbation of the forelimb ipsilateral to the cell and five out of ten responded to contralateral perturbations. 5. Perturbation of the ipsilateral hind limb was accompanied by c.s.s in four out of nine cells and latency was usually longer (by ca. 30‐40 ms). One cell showed a decrease in the probability of c.s. occurrence. Insufficient data were obtained for a systematic study of responsiveness to perturbation of the contralateral hind limb. 6. Cells showed different patterns of limb specificity, responding to perturbation of one, two or all of the three limbs studied. In total, c.s.s accompanied perturbation of at least one limb in thirteen out of twenty cells studied (65%).(ABSTRACT TRUNCATED AT 400 WORDS)
Surplus acetylcholine and acetylcholine release in the rat diaphragm.
Authors: Molenaar P C , Oen B S , Polak R L , van der Laaken A L
Published: December 2014

1. Skeletal muscles from rat, mouse and frog were incubated under different conditions and the amounts of acetylcholine (ACh) extractable from the tissue and released into the medium were determined by mass fragmentography. In some experiments measurements were made of the amounts of ACh ('bound' ACh) surviving in a muscle homogenate to which an excess of acetylcholinesterase had been added. In other experiments the membrane potentials, end‐plate potentials (e.p.p.s), and miniature end‐plate potentials (m.e.p.p.s) were studied. 2. During incubation in Ringer medium the ACh content of the rat hemidiaphragm usually did not change, but after inhibition of cholinesterase by soman the ACh content rose gradually from about 100 to 150 pmol to a plateau of about 400 pmol after 4 h. A similar formation of 'surplus ACh' after cholinesterase inhibition was found in the mouse diaphragm, but not in the frog sartorius muscle. 3. Surplus ACh accumulated predominantly in the end‐plate region of the rat diaphragm. In muscles, 16‐18 h after in vivo denervation, the capacity to form surplus ACh was decreased by more than 80%. 4. The amount of ACh diffusing from the resting hemidiaphragm into the incubation medium ('resting release') varied between 0.5 and 0.9 pmol min‐1 in different experiments; it remained at the same level during accumulation of surplus ACh. It was reduced by more than 80% 16‐18 h after denervation. 5. The amplitude of m.e.p.p.s and e.p.p.s did not increase while surplus ACh was accumulating. 6. Incubation of hemidiaphragms in Ringer solution containing [3H]choline caused the formation of [3H]ACh. Additional amounts of [3H]choline were incorporated into ACh when the nerve was stimulated for 60 min. However, incubation in the presence of soman (3,3‐dimethyl‐2‐butylmethylphosphonofluoridate), in the absence of stimulation, did not cause an increase of the [3H]ACh content of the muscles. 7. From hemidiaphragms with active cholinesterase about 120 pmol ACh was lost after prolonged nerve stimulation or incubation with 50 mM‐KCl in the presence of hemicholinium‐3, and about 35 pmol remained in the tissue. In soman‐treated muscles, containing surplus ACh, about as much ACh was released by nervous stimulation as from untreated hemidiaphragms, and much more ACh remained unreleased. 8. Transection of the muscle at both sides of the end‐plate or incubation of intact muscles in the presence of 50 mM‐KCl depolarized the muscle fibres to ‐35 and ‐31 mV, respectively. Surplus ACh was partially released by 50 mM‐KCl, but not by muscle transection.(ABSTRACT TRUNCATED AT 400 WORDS)
Variation of membrane properties in hair cells isolated from the turtle cochlea.
Authors: Art J J , Fettiplace R
Published: December 2014

1. Hair cells were enzymatically isolated from identified regions of the turtle basilar papilla and studied with the patch‐electrode technique. The experimental aim was to relate the resonance properties seen during current injection to the membrane currents measured in the same cell under whole‐cell voltage clamp. 2. Solitary hair cells had resting potentials of about ‐50 mV, and produced a damped oscillation in membrane potential at the onset and termination of a small current step; the resonant frequency varied from 9 to 350 Hz between cells, and was correlated with the region of papilla from which a cell had been isolated. The inferred frequency map was consistent with the tonotopic arrangement described previously in the intact papilla. 3. Depolarizations from the resting potential under voltage clamp activated a large net outward current with a steep voltage dependence, and the steady‐state current‐voltage relationship was strongly rectified about the resting potential. Input resistances tended to be smaller in cells with higher resonant frequencies, although there was no concurrent variation in membrane area as inferred from the cell capacitance. 4. The kinetics of the outward current evoked by a small depolarizing step depended upon the resonant frequency, fo, of the hair cell, and were slower in low‐frequency cells. On repolarization to the resting potential the current decayed exponentially with a time constant that changed from 150 ms in the lowest‐frequency cell to less than 1 ms in the highest‐frequency one. The time constant was approximately proportional to 1/f0(2). 5. Following repolarization to different membrane potentials, the tail current was found to reverse around ‐80 mV, indicating that the outward current was due mainly to K+. 6. The outward current was abolished by extracellular application of 25 mM‐tetraethylammonium chloride (TEA), or on exchange of Cs+ for K+ in the intracellular medium filling the recording electrode, each experiment supporting the contention that K+ is the major current carrier. Such treatments also removed the oscillations in membrane potential evoked by imposed current steps. 7. Addition of TEA or intracellular perfusion with Cs+ also revealed a fast inward current with an ionic sensitivity consistent with its being carried by Ca2+. Like the K+ current, the Ca2+ current was activated by small depolarization from the resting potential, and over this voltage range it was about five to ten times smaller than the K+ current. Its activation was more rapid than the fastest outward currents in high‐frequency cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Electrophysiological properties of ependymal cells (radial glia) in dorsal cortex of the turtle, Pseudemys scripta.
Authors: Connors B W , Ransom B R
Published: December 2014

1. We have investigated the electrophysiological properties of ependymal cells in the isolated dorsal cortex of the turtle, Pseudemys scripta. The cell bodies of these radial glia form an epithelium at the ventricular surface, and each cell sends one or more branching processes through the cortex to the pial surface. Very few non‐ependymal glia exist in the dorsal cortex. 2. Ependymal cells had high resting membrane potentials (‐90 mV), very fast time constants and a lack of intrinsic excitability or synaptic potentials. 3. Changes in the K+ concentration ([K+]) of the bathing solution caused near‐Nernstian changes of ependymal membrane potentials. When local neuronal pathways were activated, ependymal cells slowly depolarized while extracellular voltage shifted negatively. Simultaneous measurements of extracellular [K+] ([K+]o) near the impaled ependymal cell body showed that these slow depolarizations were fully accounted for by activity‐dependent increases in [K+]o. Similar measurements during focal pressure applications of solutions with high [K+] suggested that intrasomatic recordings reflect predominantly the [K+]o adjacent to the cell body, and not the intracortical process. 4. Intracellular injections of the fluorescent dye Lucifer Yellow CH, and simultaneous recordings from neighbouring cells, indicated that ependymal cells are chemically and electrically coupled to one another. Increasing the ambient CO2 level from 5 to 40% depolarized cells, increased their input resistance, and abolished interglial dye coupling. 5. The physiological properties of ependymal cells are very similar to those of a variety of glial cell types in a range of vertebrate and invertebrate species. In the absence of other types of glia, radial glia may function as the sole cellular mediators of K+ redistribution (i.e. K+ spatial buffering) following neural activity, as well as the generators of slow extracellular potentials.
The effects of membrane potential on active and passive sodium transport in Xenopus oocytes.
Authors: Eisner D A , Valdeolmillos M , Wray S
Published: December 2014

1. The effects of membrane potential on the Na+‐K+ pump were studied by measuring membrane current and 22Na+ efflux in voltage‐clamped Xenopus oocytes. The effects of inhibiting the Na+‐K+ pump with strophanthidin were examined. 2. Strophanthidin produced an inward shift of membrane current which reversed on removal of the drug. In control oocytes the magnitude of this current was not significantly affected by changing membrane potential over the range ‐20 to ‐160 mV. 3. In another series of experiments the intracellular Na+ concentration ([Na+]i) was elevated either by overnight Na+‐K+ pump inhibition (strophanthidin or exposure to K+‐free solutions) or by loading with nystatin. This Na+‐loading increased the magnitude of the strophanthidin‐sensitive current. The ratio of strophanthidin‐sensitive 22Na+ efflux:strophanthidin‐sensitive current was consistent with that expected from a 3Na+‐2K+ exchange. 4. When [Na+]i was elevated the strophanthidin‐sensitive current was sensitive to changes of membrane potential. Hyperpolarization from ‐20 to ‐80 mV decreased the current to 60% of control. It is suggested that the current is not sensitive to membrane potential at normal [Na+]i because the over‐all reaction is rate limited by the availability of intracellular Na+. 5. The application of strophanthidin decreased the rate of 22Na+ efflux. Both the strophanthidin‐insensitive and the strophanthidin‐sensitive components of efflux were sensitive to changes of membrane potential. The strophanthidin‐insensitive component was not greatly affected by hyperpolarization from ‐40 to ‐160 mV but was increased by depolarization to +40 mV. 6. In Na+‐loaded oocytes, the strophanthidin‐sensitive component of 22Na+ efflux was inhibited by hyperpolarization negative from ‐40 mV. Hyperpolarization from ‐40 to ‐160 mV decreased the efflux by 54 +/‐ 5%. Over the limited range of potentials for which a comparison could be made, the effects on 22Na+ efflux were somewhat less than on the electrogenic Na+‐K+ pump current. On average there was no significant effect of depolarizing from 0 to +40 mV. However, in some experiments a clear inhibition of the efflux was observed. If the oocytes were not Na+ loaded there was no significant effect of membrane potential on the strophanthidin‐sensitive Na+ efflux. 7. These results show that the effects of membrane potential on the net reaction of the Na+‐K+ pump (as measured by the electrogenic current) result partly from an inhibition of the forward mode of operation. However, there is also evidence to suggest a contribution from stimulation of the reverse reaction.
Properties of single sodium channels translated by Xenopus oocytes after injection with messenger ribonucleic acid.
Authors: Sigel E
Published: December 2014

1. The properties of fast transient Na channels induced in the Xenopus laevis oocyte plasma membrane after injection of the oocyte with foreign messenger ribonucleic acid (mRNA) were investigated with the whole‐cell voltage clamp and with the patch‐clamp technique. 2. The time course of expression and the effect of the metabolic inhibitors actinomycin D and tunicamycin were studied. The rate of channel insertion reached a maximum only about 3 days after injection with mRNA and corresponded to the incorporation of 20 active channels/s, into a single oocyte. When applied intracellularly tunicamycin blocked the appearance of active channels nearly completely while actinomycin D added to the medium had no effect. 3. The whole‐cell currents showed activation and inactivation properties reminiscent of skeletal muscle Na+ currents. The maximal peak current amplitude was 6 microA. Tetrodotoxin blocked the observed transient inward current. 50% inhibition was observed at 10 nM concentration. Veratridine depressed inactivation of the current and led to prolonged tail currents. 4. After removal of the surrounding layers of the oocyte tight seals were obtained with a patch‐clamp electrode pushed on the surface membrane. Single‐channel currents endogenous to the oocyte and Na+‐channel currents induced by injected mRNA could be recorded. The single‐channel slope conductance of the latter was 12‐15 pS. Two different types of kinetic behaviour were evident from an analysis of single‐channel currents and ensemble average currents. One type showed fast inactivation (tau less than 1 ms) and brief channel openings (less than 1 ms) whereas the second type was characterized by slower inactivation and a bursting behaviour. 5. When veratridine (75 microM) was present in the pipette solution the single‐channel behaviour was modified in a complex manner. In addition to the channel openings with normal conductance a second open state was observed with a slope conductance of 3.5 pS. This second type of channel opening could still be recorded after return to the holding potential. Its final closure followed an exponential time course with a constant time constant of 0.5 s at ‐100 mV. These events probably underlie the tail currents in the whole‐cell configuration. 6. The Xenopus oocyte represents a useful system for the study of the expression of channels induced by foreign mRNA, for the characterization of their single‐channel behaviour and for the investigation of the action of pharmacologically active substances on these channels. This system may prove useful for the study of channels that are not accessible to patch‐clamp experiments 'in situ'.
Development of ionic channels and cell‐surface antigens in the cleavage‐arrested one‐cell embryo of an ascidian.
Authors: Hirano T , Takahashi K
Published: December 2014

1. The developmental time course of the appearance of ionic channels was studied with the voltage‐clamp technique at 8 degrees C in ascidian embryos in which cleavage was arrested with cytochalasin B immediately after fertilization. The ontogeny of cell‐surface antigens was also studied using monoclonal antibodies in both normal and cleavage‐arrested embryos. The cleavage‐arrested 1‐cell embryo differentiates into a cell of epidermal type expressing Ca2+, anomalous rectifier and Ca2+‐induced K+ channels, and cell‐surface antigens against tunic. 2. The size of the Sr2+ current through egg‐type Ca2+ channels decreased during the initial 15 h and disappeared. At about 45 h a Sr2+ current reappeared; the properties of these new channels were different from those of the egg type and were considered to be those of differentiated epidermal Ca2+ channels. 3. Na+ currents also decreased during the first 15 h, and then tended to increase, reaching a peak at about 35 h before decreasing again and finally disappearing. 4. The K+ current through anomalous rectifier channels gradually increased in amplitude, reached a peak at about 35 h and then slightly decreased to a minimum at 45 h. It then increased with further development. 5. The K+ current through the Ca+‐induced K+ channels appeared at 50 h and then increased. 6. Input capacity started to increase at 15 h, attained a peak value of three times that of the egg at about 35 h, and then decreased. 7. Two anti‐tunic monoclonal antibodies, C1 and 2C5, were obtained. C1 bound only to the tunic; 2C5 bound to the tunic and to the cytoplasm of epidermal cells. 8. C1 antigens first appeared on the surface of the epidermis of the normal embryos and on the surface of the cleavage‐arrested 1‐cell embryo at about 45 h, and then increased in amount. 9. In the normal embryo 2C5 antigen was first detected at about 40 h inside epidermal cells. It started to accumulate on the epidermal surface at about 45 h and then appeared also in the tunic. In the cleavage‐arrested embryo the antigen was first detected at about 50 h, and became more intensely stained as development proceeded.(ABSTRACT TRUNCATED AT 400 WORDS)
Calcium action potential and its use for measurement of reversal potentials of horizontal cell responses in carp retina.
Authors: Murakami M , Takahashi K
Published: December 2014

1. In the carp retina perfused with a solution containing high‐Ca2+, Ba2+ and some K+‐channel blockers, the horizontal cell produced a regenerative Ca2+ action potential when the cell was depolarized by bath application of L‐glutamate (Glu) or L‐aspartate (Asp). The action potential was triggered also by a transretinal electrical stimulation which evoked an e.p.s.p. in the horizontal cell. In this solution, some cells produced the action potential spontaneously. 2. The action potential had an overshoot of about 20 mV which lasted for several seconds or even minutes. It had a threshold and showed refractoriness. In addition, it was insensitive to tetrodotoxin, but was blocked by Co2+. These observations revealed, in horizontal cells in situ, the presence of a voltage‐dependent Ca2+ channel similar to that found in dissociated cells. It is supposed that, in a physiological environment, the Ca2+ channel is prevented from becoming regenerative probably because it is counteracted by K+ channel activities. 3. Simultaneous recordings from two separate horizontal cells showed full synchronization of the Ca2+ action potentials whose amplitudes were identical. The potential uniformity thus formed in the S‐space (Naka & Rushton, 1967) enabled us to measure reversal potentials of horizontal cell responses irrespective of the electrical coupling between the cells. 4. During an overshoot of the Ca2+ action potential, an electrically evoked e.p.s.p. as well as a light response appeared with polarities reversed to those elicited at the resting state. Their reversal potentials could be estimated within a very narrow range between ‐5 and ‐10 mV. At this range, both Glu‐ and Asp‐induced potentials reversed the polarity, too. 5. These observations suggest that the ionic mechanisms are identical in the three kinds of horizontal cell response: light response, e.p.s.p. and amino acid‐induced potentials.
The action of excitatory amino acids on chick spinal cord neurones in culture.
Authors: Vlachová V , Vyklický L , Vyklický L , Vyskocil F
Published: December 2014

1. Membrane currents evoked by N‐methyl‐D‐aspartate (NMDA), L‐aspartate, L‐glutamate, quisqualate and kainate were studied in cultured neurones from the embryonic chick spinal cord by the patch‐clamp technique and by employing a quasi‐step microperfusion technique. 2. Application of NMDA, aspartate, glutamate and quisqualate induced currents which exhibited an initial peak which declined to a plateau level with a time constant of 2 s and then remained constant or slowly decreased. The discontinuation of the application was followed by an after‐current. The individual components of the responses were insensitive to TTX (2 X 10(‐6) M) and were present in neurones which did not exhibit any sign of synaptic activity. The responses induced by kainate were monophasic and declined slowly during long‐lasting application. 3. The responses induced by NMDA, aspartate and glutamate were voltage dependent, while those induced by kainate were linear between ‐80 and +80 mV. The equilibrium potential for all components of the responses to all excitatory amino acids was close to zero. 4. From dose‐response curves the half‐maximum effective dose (ED50) for glutamate and kainate was 3 X 10(‐5) and 2 X 10(‐4) M respectively. The Hill coefficients for the glutamate and the kainate were calculated to be 1.8 +/‐ 0.1 (n = 4) and 1.9 +/‐ 0.5 (n = 4) respectively. Thus two molecules may be interacting with each of the receptor‐activated ion channels. 5. Interaction between kainate and quisqualate or kainate and NMDA was studied at both negative and positive holding potentials. No summation of the responses was found when kainate at concentrations close to those required for evoking the maximum response was applied simultaneously with quisqualate or NMDA. On the contrary, a diminution of the membrane currents was observed. A marked decrease in membrane currents was also observed when glutamate (10(‐4) M) was applied simultaneously with aspartate (10(‐4) M). 6. Glutamate‐activated single‐channel currents were recorded in the cell‐attached configuration with electrodes filled with glutamate (20 microM) in five neurones and a conductance approximately 50 pS was found. 7. It is suggested that differences in the potency of the different excitatory amino acids as open‐channel blockers may be one of the mechanisms which contribute to the diversity in the action of excitatory amino acids and that at least some of the effects of NMDA, aspartate, glutamate, quisqualate and kainate may be mediated by a common receptor‐channel complex.