bluuebunny/crossref_metadata_2025 huggingface dataset:
Time course and extent of recovery in reinnervated motor units of cat triceps surae muscles
Authors: Gordon Tessa , Stein R. B.
Published: December 2014

1. Nerve and muscle properties were studied in single motor units of triceps surae muscles in the cat using chronic recording techniques and intramuscular microstimulation. Recordings were made before and at intervals up to 18 months after a nerve was sectioned and sutured either to its distal stump (nerve—nerve suture) or to a muscle directly (nerve—muscle suture). Thus, each nerve and muscle served as its own control for recovery after reinnervation.

2. Following a delay all muscles recovered their preoperative tension after nerve—nerve suture with a single exponential having a time constant of 1‐2 months. Only half the muscles recovered their preoperative tensions after nerve—muscle sutures. Muscles which did not recover fully also had a slower time course of recovery.

3. The estimated number of motor units did not increase significantly later than 2 months after nerve section and suture. Further recovery of muscle tension is due to increased unit tension, rather than increasing numbers of reinnervated motor units. Unit tension recovered completely in all muscles, but did not become enlarged, even when muscles apparently remained partially denervated.

4. The latency of compound nerve potentials often recovered completely, although the amplitude of the potential remained depressed. Single motor axonal potentials recovered to control levels after reinnervation of muscle with a time constant similar to that for the recovery of motor unit tension. Therefore, two distinct populations of motor axons contribute to the compound potential: reinnervating axons whose size recovers fully, and disconnected axons which remain atrophic. Incomplete recovery of the compound potential amplitude mainly results from a failure of all axons to remake peripheral connexions.

5. Thus, formation of functional nerve—muscle connexions completely reverses the effects of axotomy on nerve and muscle. Reinnervated motor units recovered their preoperative size, whether or not much of the muscle remained denervated.
The nature of the excitatory transmitter mediating X and Y cell inputs to the cat dorsal lateral geniculate nucleus
Authors: Kemp J. A. , Sillito A. M.
Published: December 2014

1. In experiments examining the possibility that an excitatory amino acid may be an optic nerve transmitter in mammals, excitatory amino acid antagonists have been ionophoretically applied to cells in layers A and A1 of the cat dorsal lateral geniculate nucleus and their effect on the excitatory response to visual stimulation of the receptive field centre has been assessed.

2. The antagonists used were D‐α‐aminoadipate (D‐α‐AA), DL‐α‐ε‐diaminopimelic acid (DAP), 1‐hydroxy‐3‐amino‐2‐pyrrolidone (HA‐966) and L‐glutamate diethyl ester (GDEE). The antagonist effects on the visual response were compared with their effect on similar magnitude responses evoked by ionophoretic pulses of selected agonists and a control excitant, generally acetylcholine.

3. Both D‐α‐AA and HA‐966 would selectively block or depress the visual response with respect to the response to the control excitant. At the stage the visual input was blocked, responses to the agonists N‐methyl‐D‐aspartate (NMDA), DL‐homocysteic acid (DLH) and glutamate were also greatly reduced or blocked. At dose levels below those causing a significant reduction in the visual response, D‐α‐AA and HA‐966 would selectively depress responses to NMDA and DLH with respect to the response to glutamate.

4. GDEE was relatively ineffective in blocking either agonist responses or the visual response and only produced a significant reduction in either at dose levels that caused a similar depression in the response to acetylcholine. DAP would block responses to DLH but produced no significant effect on the visual response or the responses to glutamate and acetylcholine.

5. The cholinergic antagonists atropine and dihydro‐β‐erythroidine (DHβE) blocked responses to acetylcholine without significantly reducing either visual driving or the response to DLH.

6. The effects were the same for X and Y cells in the dorsal lateral geniculate nucleus (dLGN). There was also no distinctions between ‘on’ and ‘off’ centre types of each of the two groups.

7. The significance of these results is discussed. It is argued that they reintroduce the possibility that either L‐aspartate, L‐glutamate or a similar substance may be the transmitter mediating the optic nerve input to the cat dLGN.
Stimulus‐secretion coupling in rat mast cells: inactivation of extracellular calcium dependent secretion.
Authors: Cochrane D E , Distel D L , Lansman J B , Paterson B M
Published: December 2014

1. Stimulation by compound 48/80 of mast cells deprived of Ca failed to release histamine. Secretion of histamine was elicited from such cells by the subsequent introduction of Ca. 2. Histamine secretion declined as the interval between stimulation by compound 48/80 and the introduction of Ca increased. This decline is called inactivation. 3. The addition of the ionophore, A23187, with Ca restored maximum histamine secretion overcoming inactivation. 4. Increasing the concentration of Ca introduced after stimulation, from 2 to 8 mM, or to 20 mM reduced the amount of histamine released. This reduction was proportional to the interval between stimulation and the introduction of Ca. The addition of A23187 with the higher concentrations of Ca fully restored histamine secretion. 5. Stimulation of mast cells in Ca‐free media by the secretagogues polymyxin B or bradykinin, and the subsequent introduction of Ca, resulted in a similar inactivation or decline in histamine release. 6. Mast cells inactivated by compound 48/80 stimulation in Ca‐free media showed no increase in histamine release when the secretagogues polymyxin B plus Ca or bradykinin plus Ca were added. However, when A23187 plus Ca was added, a full secretory response was obtained. 7. It is suggested that the process of inactivation involves time‐dependent change in the Ca permeability of the mast cell membrane. The concentration of introduced Ca is suggested to influence the regulation of this permeability.
Calcium fluxes in mouse mammary tissue in vitro: intracellular and extracellular calcium pools
Authors: Neville M. C. , Peaker M.
Published: December 2014

1. The total Ca content of the mammary gland increased from about 2 to 12 μmole/g tissue during the transition from pregnancy to lactation in the mouse. In tissue from lactating mice at least two thirds of the total Ca exchanged with external Ca in 6 hr. There was little non‐exchangeable Ca in tissues from pregnant mice.

2. At 37 °C the time courses of influx and efflux of 45Ca in lactating tissues could be analysed by assuming three exponential components with rate constants of about 0·3, 0·06 and 0·005 min−1 and containing, respectively, 1·7, 1·5 and 4·7 μmole 45Ca/g tissue at the steady state.

3. The rapidly effluxing component showed the time‐ and temperature‐dependence characteristic of bulk‐phase‐limited diffusion through the extracellular space. The diffusion coefficient was about one quarter of the self‐diffusion coefficient of Ca in aqueous solution, consistent with a tortuosity factor of about 2. A portion of the Ca in this component was displaced by La3+. The amount remaining in the presence of 3 m
m‐La3+ was close to that expected for free extracellular Ca. The rapid component was therefore interpreted as originating from an extracellular compartment containing both free and bound Ca.

4. The rate of efflux of the intermediate component was slowed by a factor of ten when the temperature was decreased from 37 to 0 °C giving a Q10 of 2·7, expected for membrane transport. The slow component present at 37 °C was not displaced by EGTA or La3+, suggesting that it is not localized extracellularly. It was not apparent in the 0 °C efflux curves.

5. The biphasic time course of uptake of ionophore (A23187)‐releasable 45Ca in particulate fractions obtained by homogenization and centrifugation of tissues which had been incubated with the isotope was consistent with the hypothesis that the two slower components of 45Ca flux originate from intracellular compartments. Mitochondrial uptake probably did not contribute significantly to Ca exchange in these tissues.

6. 45Calcium fluxes in mammary tissues from pregnant mice also showed three components with rate constants similar to those found in tissues from lactating mice. The amount of Ca in each component was much smaller than in lactating tissue when compared on the basis of tissue weight.

7. We conclude from these studies that: (i) intra‐ and extracellular Ca pools in mammary tissue can be distinguished on the basis of the temperature dependence of their fluxes and (ii) the transition from pregnancy to lactation is accompanied by large increases in both intra‐ and extracellular Ca pools in mammary alveolar cells.
Single‐site uptake of neutral amino acids into guinea‐pig intestinal rings.
Authors: Robinson J W , van Melle G
Published: December 2014

1. A kinetic analysis of amino acid influx into guinea‐pig small intestinal rings has been performed in an attempt to ascertain whether one or more transport sites for these substrates exists in the luminal membrane of the enterocyte. 2. No indirect correction for uptake into the extracellular space was applied, but it was assumed in the analysis that the total uptake included a diffusion term. This procedure was vindicated by the results obtained. 3. All analyses were performed by non‐linear regression techniques. In many experiments, both substrate and inhibitor concentrations were varied within the same experiment, thus giving rise to three‐dimensional diagrams describing transport processes. 4. All results pointed to the existence of a single transport agency shared by all amino acids tested. The kinetic constants, Km and Vmax, were independent of the concentration range used for their estimation; such behaviour would not be expected if several sites with different kinetic constants were available for transport. The value of KD, the constant describing the diffusive component of uptake, was the same when estimated from the uptake of an amino acid alone or when determined as the asymptote of the curve describing the inhibition of this uptake by an analogue. Finally, the Ki for an amino acid when used as an inhibitor was identical to its Km when used as substrate. This property was maintained even when the most disparate pair of amino acids, threonine and isoleucine, was examined.
Nucleoside translocation in sheep reticulocytes and fetal erythrocytes: a proposed model for the nucleoside transporter
Authors: Jarvis S. M. , Young J. D.
Published: December 2014

1. Nucleoside transport by fetal erythrocytes from nucleoside‐permeable and nucleoside‐impermeable type new‐born lambs and by reticulocytes from adult sheep was compared with that of mature erythrocytes from adult sheep of the two phenotypes.

2. Fetal cells and reticulocytes transported [U‐14C]uridine rapidly, with little difference between cells from the two types of sheep. Transport occurred by a saturable uptake mechanism with similar properties to that present in mature cells from adult nucleoside‐permeable type animals, except for an approximately 100‐fold higher Vmax.

3. This increased translocation capacity was associated with increased numbers of high‐affinity [3H]nitrobenzylthioinosine binding sites (∼ 2000‐3000 sites/cell compared with approximately 20 sites/cell for mature nucleoside‐permeable sheep erythrocytes).

4. The calculated transport capacity for each nucleoside translocation site is therefore similar in all cell types (140‐180 molecules/site. s at 25 °C, assuming that each transport site binds a single molecule of inhibitor). These values compare favourably with turnover estimates for the nucleoside transporter from human and pig erythrocytes.

5. Loss of nucleoside transport activity after birth closely paralleled loss of [3H]nitrobenzylthioinosine binding sites and the progressive loss of fetal cells from the circulation. Similarly, reticulocyte maturation in vitro was also associated with rapid loss of both nucleoside transport capacity and inhibitor binding activity.

6. p‐Chloromercuriphenylsulphonate and trypsin had no effect on [3H]nitrobenzylthioinosine binding to intact fetal cells. In contrast, both agents markedly inhibited binding to isolated ‘ghosts’ where both sides of the cell membrane were accessible to reagent. p‐Chloromercuriphenylsulphonate inhibition was markedly reduced in the presence of uridine, and reversed by addition of dithiothreitol.

7. We conclude that nucleoside transport changes during ontogeny and reticulocyte maturation in the sheep as well as species differences in nucleoside transport capacity are regulated by variations in the numbers of functional transport sites per cell rather than by changes in the activity of a constant number of sites. It is also likely that the nucleoside carrier exhibits chemical asymmetry.

8. A simple molecular model of the erythrocyte nucleoside transporter consistent with these and other known properties of the carrier is proposed.
Climbing fibre induced depression of both mossy fibre responsiveness and glutamate sensitivity of cerebellar Purkinje cells
Authors: Ito Masao , Sakurai Masaki , Tongroach Pavich
Published: December 2014

1. In high decerebrate rabbits, cells were sampled extracellularly from the rostral flocculus. Purkinje cells were identified by their characteristic responses to stimulation of the contralateral inferior olive. Identification of basket cells was based on the absence of olivary responses and also on their location in the molecular layer adjacent to identified Purkinje cells. Mass field potentials in the flocculus were also studied.

2. Single pulse stimulation of a vestibular nerve, either ipsilateral or contralateral, at a rate of 2/sec excited Purkinje cells with a latency of 3‐6 msec. This early excitation represents activation through vestibular mossy fibres, granule cells and their axons (parallel fibres). Similar early excitation also occurred in putative basket cells.

3. Conjunctive stimulation of a vestibular nerve at 20/sec and the inferior olive at 4/sec, for 25 sec per trial, effectively depressed the early excitation of Purkinje cells by that nerve, without an associated change in spontaneous discharge. The depression recovered in about ten minutes. This recovery was followed by the onset of a slow depression lasting for an hour.

4. Conjunctive vestibular—olivary stimulation produced no such depression in the following responses: early excitation in Purkinje cells induced from the vestibular nerve not involved in the conjunctive stimulation; early excitation in putative basket cells from either vestibular nerve; inhibition or rebound facilitation in Purkinje cells following the early excitation; vestibular‐evoked field potentials in the granular layer and white matter of the flocculus. These observations lead to the conclusion that the depression occurs specifically at parallel fibre—Purkinje cell synapses involved in conjunctive stimulation.

5. Ionophoretic application of glutamate to Purkinje cells in conjunction with 4/sec olivary stimulation depressed the glutamate sensitivity of Purkinje cells; aspartate sensitivity was depressed to a much lesser degree. The depression diminished in about 10 min, but this recovery was succeeded by a slow depression lasting for an hour. The depression was seen only when glutamate sensitivity was relatively high, suggesting that the micro‐electrode was impinging onto Purkinje cell dendrites. These observations suggest that subsynaptic chemosensitivity of Purkinje cells to the putative neurotransmitter of parallel fibres is involved in the depression observed after conjunctive stimulation of a vestibular nerve and the inferior olive.

6. The present results are consistent with the Marr‐Albus assumption concerning plasticity of cerebellar neuronal networks.
Long‐term synaptic enhancement and short‐term potentiation in rat fascia dentata act through different mechanisms
Authors: McNaughton Bruce L.
Published: December 2014

1. The component processes contributing to post‐activation change in synaptic efficacy in the perforant pathway to the fascia dentata were studied in rats under sodium pentobarbitone anaesthesia.

2. With low stimulus strength, which activated only a relatively small number of perforant path fibres, repetitive stimulation led to effects which had very similar characteristics to those observed at neuromuscular synapses under similar conditions. Paired shocks resulted in a short (∼ 100 ms) facilitation superimposed on a depression, possibly due to depletion of available transmitter, which recovered more slowly (∼ 4 s). Short trains of stimuli at 125‐250 Hz led to a longer lasting increase in synaptic strength which decayed to control levels with a double exponential time course. The two exponential components behaved like augmentation and potentiation at neuromuscular synapses, with time constants at 33 °C of about 5 s and about 90 s respectively.

3. High‐intensity stimulus trains of identical frequency and duration led to an enhancement of synaptic strength which lasted for longer than 30 min.

4. The paired shock depletion effect was increased in direct proportion to the amount of augmentation and potentiation present following low‐intensity stimulus trains. Following high‐intensity trains the paired shock depletion effect was increased by the same amount, and recovered with the same time course as following low‐intensity stimulus trains, even though there remained a significant enhancement of the synaptic response.

5. The results are interpreted as indicating that augmentation and potentiation are due to an increase in the probability of transmitter release whereas long‐term enhancement acts through some other, as yet undetermined, mechanism. Following high‐intensity stimulation all three processes are activated.
Hypoxic cardiac hypertrophy is not inhibited by cardioselective or non‐selective beta‐adrenoceptor antagonists.
Authors: Dennis P , Vaughan Williams E M
Published: December 2014

1. Young rabbits, eight at a time, were exposed to more than 170 hr of hypoxia (O2 at 70‐80 torr) at atmospheric pressure during 9‐11 days. 2. The animals were injected twice daily with doses of beta‐blockers up to the highest used in human therapy, or with an equivalent volume of saline. These controls were litter mates of the treated rabbits. 3. In comparison with untreated normoxic rabbits of similar age, the hypoxia induced highly significant mean increases in right ventricular dry weight (+57%, controls; +55% treated). 4. In each group, the same degree of hypertrophy was induced in the treated and control animals, irrespective of whether the drug used was a non‐selective beta‐blocker (propranolol) or a cardioselective drug (atenolol). 5. The right atria were also hypertrophied, though not as much as the right ventricles. 6. In all the hypertrophied tissues the water content was increased. 7. No significant change was observed in the dry weight or water content of the left ventricles of treated or control animals.
Effects of extracellular potassium accumulation and sodium pump activation on automatic canine Purkinje fibres
Authors: Kline Richard P. , Kupersmith Joel
Published: December 2014

1. Double barrel potassium‐sensitive micro‐electrodes were used to measure fluctuations in extracellular potassium ion concentration in large automatic canine Purkinje fibres.

2. Slow accumulations of potassium were seen in the extracellular space during prolonged beating. Following cessation of prolonged beating, a depletion of extracellular potassium ions was noted.

3. The time course of these slow changes in extracellular potassium concentration were shown to be a function of the diffusion properties of the preparation, and the rate and degree of activation of the sodium pump.

4. Action potential duration and maximum diastolic potential were simultaneously monitored during and after these periods of rapid stimulation, using conventional intracellular micro‐electrodes.

5. Initial depolarization and later hyperpolarization of the maximum diastolic potential appeared to occur as a direct result of changes in extracellular potassium concentration and level of pump activation induced by the sudden and prolonged alteration in stimulus rate.

6. Following prolonged stimulation, dramatic changes in the automatic beating rate were correlated with changes in extracellular potassium and pump rate, and their effects on the maximum diastolic potential and other parameters of the diastolic potential depolarization.

7. For some locations of the potassium‐sensitive electrode tip, large fluctuations in extracellular potassium were seen during single beats. Alterations in action potential duration during abrupt rate changes appear to derive in part from modulation by these extracellular potassium concentration fluctuations altering net membrane currents. Slower shifts in action potential duration appear correlated to the degree of sodium pump activation.
Mechanisms of transmembrane calcium movement in cultured chick embryo ventricular cells
Authors: Barry William H. , Smith Thomas W.
Published: December 2014

1. Uptake of calcium was studied in spontaneously contracting monolayers of cultured chick embryo ventricular cells. Ca exchange could be separated into two components: a rapid phase with a rate constant of 3·91/min, accounting for 1·6 nmol/mg protein; and a slower phase with a rate constant of 0·069/min, accounting for 2·7 nmol/mg protein.

2. Negatively inotropic concentrations of the slow Ca channel blocker verapamil inhibited the rapid phase of Ca uptake partially, with a maximum inhibition of 30‐40% observed at concentrations of verapamil which completely inhibited contraction.

3. The component of Ca uptake not inhibited by verapamil could be stimulated up to 25‐fold by elevation of intracellular Na concentration and reduction of extracellular Na concentration, and thus appeared to represent at least in part Ca uptake via Na—Ca exchange.

4. Ca uptake by cultured cells could be almost completely inhibited by exposure to LaCl3, 1 mmol/l, within 5 s. This same concentration of La completely inhibited contraction within 5 s.

5. During efflux of 45Ca from cells, exposure to La (1 mmol/l) slightly inhibited efflux initially with more marked inhibition of Ca influx after 3 min of La exposure. There was no evidence for a component of superficial La‐displaceable Ca, and thus the rapid phase of Ca uptake probably is due to an intracellular rapidly exchanging Ca pool. Efflux of Ca from this rapidly exchanging intracellular Ca pool was not significantly altered by exposure to Na‐free choline chloride solutions.

6. We conclude that rapid Ca uptake in these cultured myocardial cells is due primarily to Ca influx via the slow Ca channel and via Na—Ca exchange. In the presence of physiological [Ca2+]i, efflux of Ca from this intracellular Ca pool does not appear to be due to Na—Ca exchange.
Enhancement of synaptic transmission by 4‐aminopyridine in hippocampal slices of the rat.
Authors: Buckle P J , Haas H L
Published: December 2014

1. The effects of 4‐aminopyridine (4‐AP) on neurotransmission in hippocampal slices of the rat were studied in vitro. 2. Extracellular recordings of field potentials and intracellular recordings of excitatory and inhibitory post‐synaptic potentials, action potentials and TTX‐resistant spikes were obtained from the somatic and dendritic fields of CA 1 hippocampal neurones. 3. Constant perfusion with, or bolus injection of 4‐AP in micromolar concentrations resulted in substantial and persistent enhancement of the amplitude of synaptic field potentials and population spikes with no alteration of the afferent input. Somatic positive waves (p‐waves) were increased with local micro‐application of 4‐AP. 4. Intracellular recordings revealed an increase in the amplitude of e.p.s.p.s. and i.p.s.p.s. I.p.s.p.s were prolonged by 4‐AP. 5. The pyramidal cells were, after an initial hyperpolarization, depolarized by up to 10 mV during exposure to 4‐AP; the membrane conductance was not consistently changed. 6. Spontaneous shifts of the membrane potential were described as giant e.p.s.p.s and i.p.s.p.s. Spontaneous i.p.s.p.s were increased in frequency and amplitude. 7. Paired‐pulse facilitation of e.p.s.p.s was reduced by 4‐AP suggesting a presynaptic modulation of transmitter output. 8. It is concluded that 4‐AP enhances transmitter release at both excitatory and inhibitory synapses in the hippocampus.
Evidence for the role of non‐quantal acetylcholine in the maintenance of the membrane potential of rat skeletal muscle
Authors: Bray J. J. , Forrest J. W. , Hubbard J. I.
Published: December 2014

1. Resting membrane potentials of rat diaphragm muscles cultured in Trowell T8 medium were measured in vitro. After 3 hr in culture the resting membrane potential of muscle fibres within 2·5 mm of nerve section (‘near’) was ‐68·3 ± 0·4 mV (nineteen preparations). This was significantly lower (P < 0·001) than the resting potential (‐74·0 ± 0·4 mV) measured in muscle fibres 8‐10 mm from the site of nerve section (‘far’) in the same preparations. A difference between the ‘near’ and the ‘far’ fibres was maintained in muscles cultured for 6 and 12 hr. Miniature end‐plate potentials were present in both ‘near’ and ‘far’ fibres cultured for 3 and 6 hr and ceased after 12‐15 hr.

2. The presence of carbamylcholine (10−7 or 10−8 M) maintained the resting membrane potential of ‘near’ fibres close to that of ‘far’ fibres at 3, 6 and 12 hr. For example, at 3 hr in the presence of 10−8 M‐carbamylcholine the mean resting potential was 75·6 ± 0·5 mV in ‘near’ fibres and 76·1 ± 0·4 mV in ‘far’ fibres (four preparations). A similar effect was produced in preparations exposed to anticholinesterases: diisopropylphosphorofluoridate (DFP) (10−7 M), neostigmine (10−7 M) or physostigmine (10−5 M).

3. Agents that blocked acetylcholine receptors had the reverse effect. In the presence of α‐bungarotoxin (1 μg/ml.) or d‐tubocurarine (10−5 M) the resting membrane potential of ‘far’ fibres was reduced to the level of ‘near’ fibres over the 24 hr period of observation. For example, at 3 hr in the presence of α‐bungarotoxin the mean resting potential was 67·2 ± 0·5 mV in ‘near’ fibres and 68·5 ± 0·6 mV in ‘far’ fibres (six preparations). The effect of d‐tubocurarine was reversible.

4. When muscles were cultured in Ca2+‐free medium containing 1 mM‐EGTA and 10 mM‐Mg2+, there was no difference in membrane potential between ‘near’ and ‘far’ fibres and physostigmine (10−5 M) was ineffective in raising the membrane potential of ‘near’ fibres.

5. It is suggested that non‐quantal acetylcholine released from nerve terminals maintains the membrane potential of muscle fibres through a Ca2+‐dependent mechanism.
Properties of miniature excitatory junctional currents at the locust nerve‐muscle junction
Authors: Cull‐Candy S. G. , Miledi R.
Published: December 2014

1. Miniature excitatory junctional currents (m.e.j.c.s) were examined in conditions where inward current was carried mainly by Na+ (i.e. in normal medium, Ca2+‐free medium and Cl−‐free medium). M.e.j.c.s were also examined in isotonic Ca2+ where the inward post‐synaptic current was carried mainly by Ca2+.

2. In normal medium, mean m.e.j.c. amplitude = 2.34±0.05 nA. The decay time constant of m.e.j.c.s (excluding a small percentage with abnormal shapes) was τm.e.j.c. = 2.62±0.11 msec (Vm = ‐80 mV, T = 22 °C). Decay‐time was not markedly changed in Ca2+‐free or Cl−‐free medium. τm.e.j.c. approaches the life‐time of glutamate activated junctional channels.

3. Excitatory junctional currents, evoked by nerve impulses, decayed slightly faster than m.e.j.c.s obtained in the same fibres. Extracellularly recorded m.e.j.c.s and voltage‐clamped m.e.j.c.s were similar in time course.

4. τm.e.j.c. decreased exponentially with membrane hyperpolarization. An e‐fold change was produced by 182.±24.8 mV change in Vm.

5. The dependence of mean m.e.j.c. amplitude on clamp potential showed a slight non‐linearity at hyperpolarized levels. The equilibrium potential for transmitter action was close to 0 mV in normal solution as well as in Ca2+‐free and Cl−‐free solutions.

6. The kinetics of junctional channels are altered in isotonic Ca2+. M.e.j.c. amplitude was reduced to about one‐third normal size; mean m.e.j.c. = 0.74±0.03 nA. The decay time becomes markedly briefer, τm.e.j.c. = 1.01±0.08 msec, indicating a reduction in mean channel life‐time (Vm = ‐80 mV, T = 22 °C).

7. A population of slow time course and composite m.e.j.c.s appear when muscle fibres are hyperpolarized in isotonic Ca2+, thus producing a prolongation in mean τm.e.j.c.. This results from an influence of post‐synaptic membrane potential on presynaptic transmitter release. If such m.e.j.c.s are ignored the voltage dependence of τm.e.j.c. of the remaining events is abolished or even reversed indicating that voltage sensitivity of channel life‐time is altered in isotonic Ca2+. The equilibrium potential for transmitter action may be slightly more positive than normal.

8. We estimate that a single packet of neurally released transmitter normally opens, on average, 250 ion channels at these junctions.
Is the red cell calcium pump electrogenic?
Authors: Rossi J P , Schatzmann H J
Published: December 2014

1. In inside‐out vesicles of high potassium permeability, prepared from human red cell membranes, volume changes accompanying the action of the Ca2+ pump were measured by recording the intensity of light scattered by a suspension of these vesicles. Replacing Cl‐ by the impermeant gluconate anion changed swelling into shrinking. 2. Assuming that in Cl‐ media two Cl‐ ions accompany one Ca+ ion moved by the pump and in gluconate media two K+ ions are exchanged for one Ca2+ ion resulted in a good agreement between relative Ca2+ transport rate obtained from the volume change and from direct measurement of 45Ca uptake in the two media. 3. The fact that it is possible to change co‐transport of Ca with Cl‐ into counter‐transport of Ca2+ for K+ rules out that within the pump there is an obligatory coupling of Ca2+ movement with movement of another ion species (including the proton). The conclusion, therefore, is that the Ca2+ pump must be electrogenic. 4. The combination of measurement of volume change with direct measurement of 45Ca movement yielded 5‐6 microliter/mg protein for the volume of the vesicles.
An ionophoretic study of the responses of rat caudal trigeminal nucleus neurones to non‐noxious mechanical sensory stimuli.
Authors: Hill R G , Salt T E
Published: December 2014

1. Extracellular recordings of the responses of single caudal trigeminal nucleus neurones to non‐noxious and noxious facial stimuli and to ionophoretically applied L‐glutamate, L‐aspartate and acetylcholine were made in urethane anaesthetized rats. 2. Neurones excited by non‐noxious mechanical stimuli were located primarily in the magnocellular part of nucleus caudalis, whereas neurones excited by both noxious and non‐noxious stimuli were located either ventromedially to the magnocellular part of nucleus caudalis or superficially to the substantia gelatinosa. 3. Both L‐aspartate and L‐glutamate were found to excite all neurones tested in nucleus caudalis. In contrast, however, acetylcholine was found to excite only 31% of the neurones tested. 4. Responses of nucleus caudalis neurones to non‐noxious sensory stimulation were not antagonized by the excitatory amino acid antagonist D‐alpha‐aminoadipate, but were antagonized by cis‐2, 3‐piperidine dicarboxylate and gamma‐D‐glutamylglycine, two excitatory amino acid antagonists with a broader spectrum of action. 5. It is concluded that the chemical synaptic transmitter of non‐nociceptive mechanoreceptive primary afferent fibres to nucleus caudalis may be a ligand for an excitatory amino acid receptor other than a D‐alpha‐aminoadipate‐sensitive receptor. The synaptic receptor may thus be of the kainate or quisqualate type, and the transmitter possibly L‐glutamate, L‐aspartate or an as yet unidentified substance.
Kinetics of thiamine transport across the blood‐brain barrier in the rat.
Authors: Greenwood J , Love E R , Pratt O E
Published: December 2014

1. By measurement of the rate of disappearance of injected tracer thiamine from the bloodstream, a programme for the continuous injection of thiamine at a variable rate has been devized by which a steady raised level can be achieved rapidly and maintained in the circulation. By this means the flux of radioactive thiamine across the blood‐brain barrier has been measured. 2. In separate experiments progressively higher levels of thiamine were maintained in the bloodstream. Evidence was obtained that the transport of thiamine across the blood‐brain barrier is a carrier‐mediated process which can be saturated by raised levels of thiamine. 3. The saturation of the transport process was incomplete: kinetic analysis showed that there was a non‐saturable component of the transport which was probably due to passive diffusion. 4. The contribution of the non‐saturable component was normally small and is probably insufficient to meet the needs of the brain for the vitamin unless the concentration of the vitamin in the blood is raised considerably above normal. 5. This two‐component transport process had substantially similar kinetic parameters in different regions of the brain.
Induction and removal of inward‐going rectification in sheep cardiac Purkinje fibres
Authors: Carmeliet E.
Published: December 2014

1. In sheep cardiac Purkinje fibres superfused with K‐free, Na‐free medium, the membrane potential can be stable either at a low negative level (‐50 mV) or at a high negative level (‐100 mV). The mechanism underlying the existence of these two stable potential levels was investigated using the two‐micro‐electrode voltage‐clamp technique.

2. By applying a voltage clamp of a certain duration at an appropriate level the membrane potential could be shifted from one stable level to the other. The shift was observed in Cl‐free medium, excluding a redistribution of Cl as a possible explanation.

3. Currents during and following a voltage step and their change with amplitude and duration of the voltage step could not be explained on the basis of depletion or accumulation of K ions in the narrow extracellular clefts.

4. Instantaneous currents determined from the high negative resting level showed a high conductance and a pronounced inward rectification, while measurements from the low negative resting level indicated a low conductance and absence of inward rectification. The steady‐state current—voltage relation was dependent on the holding potential and showed memory or hysteresis.

5. Estimation of the conductance by superimposed short voltage‐clamp pulses showed an increase in conductance during a hyperpolarizing clamp from the low negative level and a decrease in conductance during a depolarizing clamp from the high negative level. The time‐dependent current during a hyperpolarizing clamp from the low negative level reversed direction at a potential level corresponding to EK, assuming a cleft K concentration of about 1 mM. In the presence of 0·1 mM‐Ba the time‐dependent current was abolished.

6. The results suggest that the shift between the two stable levels is due to a time‐dependent conductance change in the K inward rectifier channel, iK1. The existence of memory excludes activation or de‐activation only depending on the voltage gradient. Interaction of extracellular K ions with a site in the membrane is proposed as the activating mechanism.
Calcium channel and calcium pump involved in oscillatory hyperpolarizing responses of L‐strain mouse fibroblasts
Authors: Okada Yasunobu , Tsuchiya Wakoh , Yada Toshihiko
Published: December 2014

1. In fibroblastic L cells, spontaneously repeated hyperpolarizing responses (oscillation of membrane potential) and hyperpolarizing responses evoked by electrical stimuli were suppressed by the external application of a K+ channel blocker, nonyltriethylammonium (C9). This hydrophobic TEA‐analogue also inhibited the hyperpolarization induced by intracellular Ca2+ injection.

2. Quinine or quinidine, known inhibitors of the Ca2+‐activated K+ channel of red cells, instantaneously inhibited these hyperpolarizations. Thus, these hyperpolarizations are likely to be caused by the operation of Ca2+‐sensitive K+ channels.

3. Azide, which is known to inhibit the mitochondrial Ca2+ uptake in fibroblasts, and caffeine, dantrolene Na and oxalate, which affect the microsomal Ca2+ transport, did not exert any effects upon the electrical potential profiles.

4. On the other hand, Ca2+ channel blockers (nifedipine, D 600 and Co2+) suppressed the hyperpolarizing responses, but not the hyperpolarizations produced by intracellular Ca2+ injection, suggesting that the calcium ions responsible for the hyperpolarizing responses are mainly derived from outside the cell through Ca2+ channels.

5. Flavones of plant origin, which are known to inhibit Ca2+‐ATPase, prolonged the duration of the hyperpolarizing phase of the oscillation or produced a sustained hyperpolarization.

6. It is concluded that the Ca2+ channel and the Ca2+ pump play essential roles in the generation of the hyperpolarizing response and of the membrane potential oscillation in L cells, and that these hyperpolarizations are brought about by a transient elevation of cytosolic Ca2+ level which, in turn, activates Ca2+‐dependent K+ channels.
Extrinsic innervation of the canine abdominal vena cava and the origin of cholinergic vasoconstrictor nerves
Authors: Nakazato Y. , Ohga A. , Shigei T. , Uematsu T.
Published: December 2014

1. The effects of electrical stimulation of the greater splanchnic nerve and the vagus nerve on the middle segment of the inferior vena cava (i.v.c.) were studied in anaesthetized and unilaterally or bilaterally adrenalectomized dogs. The vascular response of the segment was measured as the change in pressure of an intravascular cuff inserted into the lumen of the segment.

2. Electrical stimulation of the greater splanchnic nerve of either side caused an increase in the tension of the vein with a delay of less than 3 sec. The tension increased with frequency of stimulation until it reached a maximum at the frequency of 32 Hz. The maximum tension development was consistently larger, by a factor of about two, when the right greater splanchnic nerve was stimulated than when the left was. It seems that the right greater splanchnic nerve supplies more sympathetic nerve fibres to the middle segment of the i.v.c. than does the left.

3. The response to electrical stimulation of the right or left greater splanchnic nerve was markedly reduced by phentolamine or hexamethonium. The response remaining after treatment with phentolamine or hexamethonium was augmented by neostigmine and diminished by atropine.

4. The electrical stimulation of the vagus nerve elicited no response of the vein before and after treatment with neostigmine.

5. The effects of electrical stimulation of the right greater splanchnic nerve were further confirmed by a preparation in which the middle segment of the i.v.c. was perfused with Krebs solution in situ. The relation between the frequency of stimulation and the magnitude of the response was almost the same as in the in vivo experiments.

6. It was also confirmed in the perfused preparation that the response to electrical stimulation of the right greater splanchnic nerve was reduced by phentolamine and the remaining response was augmented by neostigmine and abolished by atropine.

7. Our data show that the middle segment of the canine i.v.c. receives both adrenergic and cholinergic excitatory innervation, preferentially via the right greater splanchnic nerve.

8. The infrarenal segment of the i.v.c. was also examined in the in vivo experiment, in which it was shown that this segment received much clearer dominant innervation of the right greater splanchnic nerve.

9. The infrarenal segment of the i.v.c. is also supplied with excitatory adrenergic fibres and, in some cases, with the cholinergic ones from the right greater splanchnic nerve.
Kinetics of the sodium pump in the frog choroid plexus.
Authors: Saito Y , Wright E M
Published: December 2014

1. Active Na+ transport across the choroid plexus is mediated by Na‐K pumps in the brush border membrane of the epithelium. We have studied the kinetics of Na+ pumping across the brush border membrane using a 22Na efflux procedure. 2. Frog choroid plexuses were loaded with 22Na in K+ ‐free, cold Ringer solution containing various Na+ concentrations. The efflux of 22Na from the tissues was monitored at 22 degrees C and the rate constant (k) was estimated for each flux interval. The pump component was obtained from the change in k(delta k) induced by the addition of KCl to the superfusate. 3. Ouabain blocked this K+ ‐sensitive Na+ efflux and other monovalent cations substituted for K+ in the sequence Tl+, Rb+, K+, greater than NH+4 greater than Cs+ much greater than Li+. Active sodium transport (delta k x Nac) increased in a sigmoidal and saturable way with intracellular Na+ and with extracellular K+ concentrations. 4. Kinetic parameters were estimated using the model of Garay & Garrahan (1973). The data indicate that there were two ligand binding sites for K+ on the outside face and three ligand binding sites for Na+ on the cytoplasmic face of the pump. The Kms for potassium and sodium were 1 . 1 and 7 mM. 5. The results also suggest that the Na‐K pump has a coupling ratio of 1 . 5. We conclude that the Na‐K pump in this epithelium is very similar to those in single cells such as erythrocytes, nerve and muscle.
Transport specificity for neutral and basic amino acids at maternal and fetal interfaces of the guinea‐pig placenta
Authors: Eaton B. M. , Mann G. E. , Yudilevich D. L.
Published: December 2014

1. The unidirectional influx of amino acids into the guinea‐pig syncytiotrophoblast was measured using a single circulation paired‐tracer dilution technique which allows separate characterization of both fetal and maternal interfaces. An in situ preparation perfused through the fetal circulation was used to examine the fetal side, while an isolated preparation perfused through both the fetal and maternal circulations was used to study both interfaces simultaneously.

2. On the fetal side the maximal uptake (Umax) determined at tracer concentrations was high for the short‐chain neutral amino acid alanine (76%) and the long‐chain neutrals, leucine (75%), phenylalanine (90%) and tyrosine (82%) and for the basic amino acid lysine (65%). In contrast, Umax was negligible for α‐methylaminoisobutyric acid and taurine, a β‐amino acid.

3. The uptake of alanine and phenylalanine on the fetal side was inhibited by both short‐chain (alanine, serine, cysteine) and long‐chain (phenylalanine, methionine, leucine) neutral amino acids.
d‐alanine had no effect on
l‐alanine uptake whereas
d‐phenylalanine significantly inhibited that of
l‐phenylalanine. Diaminobutyric acid, lysine and arginine were effective inhibitors of alanine uptake but had no effect on phenylalanine uptake.

4. On the maternal side uptake of alanine, phenylalanine and lysine was measured. Over a wide range of concentrations self‐inhibition of alanine influx was similar to the cross‐inhibition observed with phenylalanine. In contrast, the influx of phenylalanine, which was strongly self‐inhibited, was only partially cross‐inhibited by alanine.

5. Influx of alanine and phenylalanine was measured at various perfusate concentrations and was found to be saturable on both maternal and fetal sides. The data were fitted to a single hyperbola and, on the maternal side, the Km for alanine (10.3±2.7 m
m, mean±
s.e., n = 3) was three‐fold higher than the value measured for phenylalanine (3·1±0·8 m
m). On the fetal side the Km values for alanine (8·4±1·4 m
m, n = 4) and phenylalanine (11·9±1·9 m
m, n = 3) were similar.

6. The uptake of alanine, phenylalanine and lysine appeared to be highly sodium‐dependent accounting for 40‐70% of the total influx. However, the inhibited fractions were found to be different on the two sides of the placenta.

7. The results of uptake, cross‐inhibition and Na+‐dependency experiments suggest the presence of an alanine‐serine‐cysteine (ASC) type system and a leucine (L) type system with markedly overlapping specificities at both the fetal and maternal interfaces. Separate kinetic characterization of a two carrier system was not possible under the conditions of these experiments. However, kinetic parameters for the over‐all transport of alanine and phenylalanine were measured.
Noradrenaline receptors on the rat basilar artery.
Authors: Hirst G D , Neild T O , Silverberg G D
Published: December 2014

1. Intracellular recordings were obtained from the arterial smooth muscle cells of rat basilar artery during perivascular nerve stimulation and during the application of adrenoceptor agonists and antagonists. 2. Perivascular nerve stimulation evoked excitatory junction potentials. Increased stimulation resulted in action potentials which were associated with arterial constriction. 3. Bath‐applied noradrenaline did not cause constriction but at high concentrations caused membrane depolarization. The depolarization caused by a given dose of noradrenaline was larger in the presence of cocaine. 4. Neither the depolarizations obtained by nerve stimulation nor those obtained by bath‐applied noradrenaline were blocked by adrenoceptor blocking agents. 5. Unlike alpha‐receptors, the receptors on the rat basilar artery were activated equally well by dopamine, adrenaline, and both optical isomers of noradrenaline. 6. Excitatory junction potentials could be obtained in the presence of high bath concentrations of noradrenaline.
Two components in the cellular response of rat tail arteries to nerve stimulation.
Authors: Cheung D W
Published: December 2014

1. The response of rat tail arteries to stimulation of perivascular nerves was studied with intracellular micro‐electrodes. 2. E.j.p.s were recorded from all smooth muscle cells. With higher stimulus strength, a slow depolarization that lasted for more than 30 sec also appeared. Repetitive stimulation was more effective in eliciting this slow component than were single pulses. 3. E.j.p.s were resistant to phentolamine and yohimbine. However, guanethidine and sympathetic denervation with reserpine and 6‐hydroxydopamine depressed e.j.p.s. 4. The slow depolarization was readily blocked by phentolamine (1 x 10(‐6) g/ml.) and potentiated by cocaine (1 x 10(‐6) g/ml.). 5. It is proposed that vascular smooth muscle activity can be regulated neurally by both the e.j.p. and the slow depolarization.