bluuebunny/crossref_metadata_2025 huggingface dataset:
Colonic motility and transit of digesta during hard and soft faeces formation in rabbits.
Authors: Ehrlein H J , Reich H , Schwinger M
Published: December 2014

Rabbits produce hard and soft faeces in a circadian rhythm. This study was undertaken in order to examine the motor function of the colon in relation to the formation of these two types of faeces. Colonic motility was measured in unanaesthetized rabbits using strain‐gauge transducers and simultaneous radiography. Three types of contractions were found in the rabbit proximal colon: haustral activity, segmental activity, and mass peristalsis. Distinctly different motor patterns were observed during the formation of hard and soft faeces. When hard faeces were produced, the motor activity of the proximal colon was enhanced. It consisted of segmental and haustral activity. The segmental contractions separated the digesta into faecal pellets and forced them slowly aborad, whereas the movements of the haustra carried the liquid contents back towards the caecum. When soft faeces were produced haustral and segmental activity was reduced and transfer of the digesta through the proximal colon was accelerated by mass movements. In contrast to the proximal colon, the motility of the distal colon was enhanced during the formation of soft faeces and decreased during the production of hard faeces. The results support the concept that hard faeces are chiefly produced by a separation of liquids and solids and by a retrograde transfer of liquid digesta rather than by an increased absorption of water.
Shared reflex pathways from Ib tendon organ afferents and Ia muscle spindle afferents in the cat.
Authors: Jankowska E , McCrea D A
Published: December 2014

The possibility was investigated that group Ia muscle spindle afferents and group Ib tendon organ afferents influence spinal motoneurones via shared neuronal pathways. Mutual facilitation of actions of these afferents at a premotoneuronal level has been taken as evidence that they use the same interneurones to evoke post‐synaptic potentials (p.s.p.s) in motoneurones. Inhibitory p.s.p.s (i.p.s.p.s) or excitatory p.s.p.s (e.p.s.p.s) were evoked in motoneurones by selective activation of group Ia afferents or group Ib afferents. P.s.p.s following stimulation of both Ia and Ib afferents were then compared with the arithmetic sum of p.s.p.s evoked by each of them separately. When the former were larger the difference was used as a measure of synaptic actions mediated by interneurones co‐excited by Ia and Ib afferents. Both excitatory and inhibitory pathways to motoneurones have been found to be shared by Ia and Ib afferents, although the proportion of interneurones actually used in common by these afferents could not be established. The latencies of post‐synaptic actions mediated by such interneurones indicated that they were evoked disynaptically or trisynaptically. The study leads to two main conclusions: that group Ia muscle spindle afferents, and in consequence also fusimotor systems, may modulate the reflex action of tendon organs, and that the two groups of afferents are a source of information in a common feed‐back system.
Development of sympathetic innervation to proximal and distal arteries of the rat mesentery.
Authors: Hill C E , Hirst G D , van Helden D F
Published: December 2014

The changes which occur during the post‐natal development of sympathetic innervation to proximal and distal arteries of the rat mesentery have been examined using intracellular recording and histochemical techniques. In the youngest animals examined, single perivascular stimuli initiated slow depolarizing potentials which were not calcium‐dependent. After day 4, single stimuli failed to initiate membrane potential changes in a proportion of preparations. This stage coincided with the period of extensive ramification of sympathetic nerve fibres over the surface of the arterioles. From day 9 onwards, membrane potential changes were again initiated by single stimuli in the distal arteries. These responses were distinct from those recorded from the younger animals and in many ways resembled excitatory junction potentials recorded from the arteries of mature animals. There was a gradient in the development of the innervation to the arteries of the rat mesentery, with that to the distal vessels maturing earlier than that to the more proximal vessels.
Effects of streptozotocin diabetes and fasting on intracellular sodium and adenosine triphosphate in rat soleus muscle.
Authors: Moore R D , Munford J W , Pillsworth T J
Published: December 2014

The hypothesis that part of the insulin transduction system consists of a co‐ordinated stimulation of the Na pump and of Na‐H exchange by the hormone (Moore, 1981) requires that insulin plays a physiological role in the regulation of intracellular Na+. Moreover, this model predicts that in hypoinsulinaemic states, such as diabetes and fasting, intracellular pH and intracellular ATP levels would be depressed. The present study tests the hypothesis that in hypoinsulinaemic states intracellular Na+ is increased and intracellular ATP is decreased by measuring these parameters in soleus muscles removed from both diabetic and fasted rats. When rats were made diabetic by injection of streptozotocin (SZ) plasma insulin significantly decreased by 24 hr and plasma glucose and triglyceride levels increased. Intracellular Na+ was significantly elevated by 48 hr after injection of SZ. The elevation ranged from 18 to 48% and persisted for the duration of the experimental observation (up to 28 days). Intracellular ATP decreased significantly by the seventh day after SZ injection and remained depressed by about 24% for the duration (35 days) of the observation. In one series, a significant negative correlation was seen between plasma insulin levels and intracellular Na+ of both SZ‐diabetic animals and their controls. Intracellular Na+ also significantly increased when hypoinsulinaemia was induced by fasting. Again, intracellular ATP did not decrease until after the elevation of intracellular Na+. After 72 hr of fasting, intracellular ATP was still decreased in spite of normal plasma glucose levels. Insulin therapy of SZ diabetic rats restored intracellular ATP and plasma glucose to normal, but did not restore intracellular Na+ to normal levels. The results confirm two predictions of the ‘insulin transduction system model (Moore, 1981). Most strongly supported is that part of the model which indicates that the Na pump is regulated by physiological levels of insulin. This is especially convincing since hypoinsulinaemia produced by a non‐pharmacological procedure, fasting, was associated with an increase in intracellular Na+.
The dependence of the colour and brightness of a monochromatic light upon its angle of incidence on the retina.
Authors: Alpern M , Kitahara K , Tamaki R
Published: December 2014

The changes in brightness and colour of a monochromatic test light as its angle of incidence on the retina was changed from normal (pupil centre traverse) to oblique (3.5 mm temporal pupil traverse), was measured by matching it with three normally incident primaries. Results on two normal trichromats were generally in accord with published data on the Stiles‐Crawford intensity and colour effects. One observer was also the subject of the preceding paper (Alpern & Kitahara, 1983) in which the field sensitivities of his foveal IIj(mu) (j = 3, 4, 5) mechanisms for normally, and obliquely, incident backgrounds were reported. For normal incidence, the colour matching functions are in rough accord with expectation if the action spectra of the three cone mechanisms, which provide the photoreceptor basis for his trichromacy, were the same IIj mechanisms for normal incidence. A unified theory is developed for both Stiles‐Crawford intensity and colour effects, assuming that the same visual pigments in the same set of univariantly signalling cones absorbs both the normal incident primaries and the obliquely incident test. Given no free parameters for curve fitting, the Stiles‐Crawford intensity effect data are in reasonable agreement with the theory if the photoreceptor basis of these matches were the normally and obliquely incident IIj(mu) mechanisms. The Stiles‐Crawford colour effect data contradict the expectations of the unified theory applied with these same IIj(mu) mechanisms. Either II3(mu) is not a valid operational definition of the action spectrum of his short‐wave sensitive photoreceptors or at least one assumption of the unified theory is false.
Intraventricular injections of drugs which inhibit phospholipase A2 suppress fever in rabbits.
Authors: Cranston W I , Hellon R F , Mitchell D , Townsend Y
Published: December 2014

Injection of two chemically dissimilar inhibitors of phospholipase A2 (mepacrine and parabromophenacylbromide) into the cerebral ventricles of rabbits inhibited the febrile response to endogenous pyrogen given by the same route. 2. The same doses of the inhibitors given intravenously did not affect the febrile response to endogenous pyrogen given into the ventricles, indicating that their action was central. 3. When given intraventricularly the inhibitors did not affect the maintenance of core temperature in a cold environment, indicating that they did not impair thermoregulatory ability. 4. The inhibitors had no effect on the temperature rise following intraventricular injection of arachidonic acid. 5. These observations are compatible with the proposition that one or more metabolic products of arachidonic acid other than prostaglandin are involved in pyrogenesis.
Effects of a spider toxin on the glutaminergic synapse of lobster muscle.
Authors: Abe T , Kawai N , Miwa A
Published: December 2014

We studied the effect of neurotoxin (JSTX) separated from spider venom on the lobster neuromuscular junction. JSTX selectively suppressed excitatory post‐synaptic potentials (e.p.s.p.s) without affecting the inhibitory post‐synaptic potentials (i.p.s.p.s). The effect of JSTX was dose‐dependent. The threshold dose for suppressing e.p.s.p.s corresponded to a small fraction of the toxin amount in a venom gland. At high concentration, JSTX irreversibly blocked e.p.s.p.s. The reduction in amplitude of extracellularly recorded e.p.s.p.s after JSTX application followed an exponential time course. The rate of suppression increased proportionally with the toxin concentration. JSTX blocked the glutamate potential in the post‐synaptic membrane but it failed to affect the aspartate‐induced depolarization. Kainic acid potentiated the glutamate‐induced depolarization but it was without effect in the presence of JSTX. Depolarization produced by quisqualic acid is suppressed by the toxin. Our results suggest that the spider venom contains specific blockers of glutamate receptors in crustacean neuromuscular junctions.
Effects of hypoxia on polysynaptic hind‐limb reflexes in new‐born lambs before and after carotid denervation.
Authors: Blanco C E , Dawes G S , Walker D W
Published: December 2014

Polysynaptic reflex responses in the hind limb were obtained by stimulating the peroneal nerve in unanaesthetized lambs between 4 and 12 days from birth, before and after carotid denervation. In intact lambs isocapnic reduction of the Pa,O2 from 88 to 31 or to 23 mmHg caused an insignificant decrease in reflex amplitude. Denervation of the carotid bifurcations induced hypoventilation. When the Pa,O2 was then reduced to 22 mmHg the reflex amplitude fell by 77%. In carotid denervated lambs after complete transection of the spinal cord at T12‐L1, reduction of the Pa,O2 to 23 mmHg did not alter the size of the reflex. The same result was observed after section of the dorsal part of the lateral funiculi. It is concluded that, in the young lamb a few days after birth, the afferent activity of the carotid chemoreceptors during hypoxia plays an important role in maintaining the excitability of motor reflexes. The possible mechanisms are discussed.
The relation of neuromuscular synapse elimination to spinal position of rabbit and rat soleus motoneurones.
Authors: Gordon H , van Essen D C
Published: December 2014

We have examined recent claims that neuromuscular synapse elimination occurs preferentially among motoneurones from the more rostral of the two spinal roots contributing to the soleus muscle of the rat. The number of synapses made by individual motoneurones contributing to the soleus muscles of the rabbit and rat were estimated at different stages of post‐natal development. The assay was based on measurements of twitch tensions in response to stimulation of individual motor axons in ventral root filaments. Contrary to the previous claims, we found that synapses were lost by motoneurones passing through all contributing spinal roots in both the rabbit and rat. Furthermore, in both species there was little or no difference in the extent of synapse elimination associated with the various spinal roots.
Inhibition of the sodium pump in guinea‐pig ventricular muscle by dihydro‐ouabain: effects of external potassium and sodium.
Authors: Daut J
Published: December 2014

The inhibition of the electrogenic pump current in quiescent guinea‐pig ventricular muscle by dihydro‐ouabain (DHO) was studied with the three‐micro‐electrode voltage‐clamp technique described previously (Daut, 1982c). From dose‐response curves of the drug‐induced current change (ID) the equilibrium dissociation constant of the binding of DHO to the Na‐K pump (KD) and the electrogenic pump current flowing in the steady state (Ip) were inferred (Daut & Rüdel, 1982b). The external K concentration ([K]o) was varied between 2 and 4.5 mM (substituted by Na). KD was found to increase with increasing [K]o. A plot of log KD versus log [K]o gave a straight line with a slope of about 1.5. The time constants of the onset (tau on) and decay (tau off) of ID are supposed to represent the chemical kinetics of binding and unbinding of the drug (Daut & Rüdel, 1981, 1982b). Tau on was found to be inversely related to [K]o whereas tau off was found to be independent of [K]o. Ip was found to be independent of [K]o. This was interpreted to indicate that in the steady state Ip is mainly determined by the passive influx of Na into the cell, which may be relatively insensitive to small changes in [K]o. The effects of [K]o on the drug‐induced current change are consistent with competitive inhibition of the binding of DHO to the Na‐K pump. It is suggested that K ions and cardiac glycosides compete for extracellular binding sites on the same conformation of the Na‐K pump. The external Na concentration ([Na]o) was varied between 147 and 49 mM (substituted by choline or Tris). Reduction of [Na]o produced a proportional decrease of Ip. This may be a consequence of the accompanying reduction of passive Na influx and the resulting decrease in intracellular Na activity (alpha iNa). Reduction of [Na]o markedly increased KD. This effect may be mediated by competition between Na and K at the K‐loading sites of the pump and/or by separate modulatory Na‐binding sites. It is concluded that the well known effects of external Na and K on the positive inotropic action of cardiac glycosides can be fully accounted for by the marked changes in the apparent binding affinity of the drug reported here.
Furosemide fails to alter plasma active or inactive renin in conscious sheep but does so in anaesthetized animals.
Authors: Lush D J , Munday K A , Noble A R
Published: December 2014

Regulation of plasma levels of active and inactive renin was investigated using sheep with indwelling artery, vein and bladder catheters. Control and experimental studies were carried out in the same animals on different days. Volume depletion during any single experiment was limited to a maximum of 50 ml. Despite large changes in sodium and water excretion, the diuretic furosemide at two dose levels, 1 and 10 mg/kg, failed to alter plasma levels of either active or inactive renin in conscious sheep. Induction of pentobarbitone anaesthesia in the sheep did not, per se, alter either plasma active or inactive renin. Furosemide (10 mg/kg) in anaesthetized animals produced a similar diuresis and natriuresis response to conscious sheep, but plasma active renin increased by 270% and inactive renin decreased to zero. In conscious sheep given an infusion of papaverine, furosemide also produced an increase in plasma active renin and a concurrent decrease in the inactive form. In both anaesthetized animals and in conscious sheep infused with papaverine, furosemide‐induced intrarenal vasodilation, as evidenced by changes in clearance of p‐aminohippuric acid, was much reduced in comparison to the conscious animals. This may be significant in relation to the control of renin secretion. It appears that the macula densa sodium receptor, which is considered to regulate renin release, will only function after it has been primed by other intra‐ or extrarenal factors. This is discussed, particularly in relation to the possible role played by the prostaglandin system.
Aequorin‐calcium transients in frog twitch muscle fibres.
Authors: Eusebi F , Miledi R , Takahashi T
Published: December 2014

Intracellular Ca2+ transients, evoked either by action potentials or depolarizing clamp pulses, were studied in frog sartorius muscle fibres injected with aequorin. The time course of the Ca2+ transients became shorter as the temperature was increased. The half rise time and decay time constants showed straight lines between 3 and 30 degrees C in Arrhenius plots, with a Q10 of 2.5 and 2.3 respectively. The potential dependence of the Ca2+ transient was examined under voltage clamp. The peak light amplitude reached a plateau at around +50 mV, suggesting that Ca2+ release continues beyond the potential level at which contraction was saturated. During a prolonged depolarization, the Ca2+ transient gradually declined. The time course of decline became faster when long depolarizing pulses were repeated, or when the temperature was increased. The Q10 for half duration of the Ca2+ transient evoked by prolonged depolarization was 2.2. A Ca2+ transient could be evoked in Ca2+‐free Ringer solution containing EGTA. Formamide, which is known to abolish excitation‐contraction coupling, also abolished the Ca2+ transient. During maintained depolarization, the time integral of the Ca2+ transient was larger for larger depolarizations, suggesting that the total amount of Ca2+ released was greater for the more intense depolarization. The decline of the Ca2+ transient during maintained depolarization is probably due to inactivation of excitation‐contraction coupling rather than the depletion of intracellular Ca2+ stores. These findings support the view that in frog skeletal muscle fibres the increase in intracellular Ca2+, caused by membrane depolarization, is produced by the release of Ca2+ from intracellular stores and that any influx of Ca2+ from the external medium does not contribute appreciably to the aequorin‐Ca2+ transient.
Potassium channel distribution in spinal root axons of dystrophic mice.
Authors: Bostock H , Rasminsky M
Published: December 2014

We have used 4‐aminopyridine (4AP), a potassium channel blocker, to assess the presence and distribution of potassium channels in the congenitally abnormally myelinated spinal root axons of dystrophic mice. 1 mM‐4AP slightly depressed the amplitude but had no effect on the half‐width of the monophasic action potential of normal A fibres, indicating the absence of a significant concentration of potassium channels at normal mouse nodes of Ranvier. By progressively increasing stimulus intensity it was possible to elicit three more or less discrete components of the compound action potential from dystrophic mouse spinal roots, presumably corresponding to myelinated fibres, large diameter bare axons and, in the case of dorsal roots, C fibres. The amplitude and duration of all three components were increased on exposure to 4AP, indicating the presence of potassium channels in all types of dystrophic mouse spinal root axons. Conduction in single fibres was studied using longitudinal current analysis. Both saltatory and continuous conduction were observed corresponding to the myelinated and bare portions of dystrophic mouse spinal root axons. Three types of ‘nodal’ membrane could be inferred from the membrane current recordings from myelinated dystrophic mouse axons: (1) pure sodium channel membrane, (2) membrane containing both sodium and potassium channels, and (3) membrane containing predominantly, if not exclusively, potassium channels. The large early outward currents at the latter two types of nodes suggested that these nodes were wider than normal. Recordings of continuous conduction indicated that potassium channels were also distributed irregularly along bare portions of the dystrophic mouse axons. These abnormalities of ion channel distribution are interpreted as reflecting failure of normal axon‐Schwann cell communication in the dystrophic mouse spinal roots.
Modification of potassium movement through the retina of the drone (Apis mellifera male) by glial uptake.
Authors: Coles J A , Orkand R K
Published: December 2014

Intracellular recordings were made in photoreceptors and glial cells (outer pigment cells) of the superfused cut head of the honey‐bee drone (Apis mellifera male). When the [K+] in the superfusate was abruptly increased from 3.2 mM to 17.9 mM both photoreceptors and glial cells depolarized. The time course of the depolarization of the photoreceptors was slower with increasing depth from the surface. Half time of depolarization was plotted against depth: this graph was compatible with the arrival of K+ being exclusively by diffusion through the extracellular clefts. However, as we then showed, this interpretation is inadequate. The time course of depolarization of the glial cells was almost the same at all depths. This indicates that they are electrically coupled. Consequently, current‐mediated K+ flux (spatial buffering) through glial cells will contribute to the transport of K+ through the tissue: K+ ions enter the glial syncytium in the region of high external potassium concentration, [K+]0, and an equivalent quantity of K+ ions leave in regions of low [K+]0. Intracellular K+ activity (aiK) was measured with double‐barrelled K+‐sensitive micro‐electrodes in slices of retina superfused on both faces. When [K+] in the superfusate was increased from 7.5 mM to 17.9 mM an increase in aiK was observed in glial cells at all depths in the slice (initial rate 1.7 mM min‐1, S.E. of the mean = 0.2 mM min‐1), but there was little increase in the photoreceptors (0.3 +/‐ 0.2 mM min‐1). The increase in aiK in glial cells near the centre of the slice could not have been caused by spatial buffering; it presumably resulted from net uptake. We conclude that when [K+] is increased at the surface of this tissue, the build up of K+ in the extracellular clefts depends on extracellular diffusion, spatial buffering and net uptake. The latter two processes, which have opposing effects, involve about 10 times as much K+ as the first. This is in rough agreement with less direct experiments on mammalian brain (Gardner‐Medwin, 1977, 1983b).
Structural and functional analysis of synaptic transmission between identified leech neurones in culture.
Authors: Henderson L P , Kuffler D P , Nicholls J , Zhang R
Published: December 2014

The fine structure and physiological properties of chemical synapses that develop between identified leech neurones in culture have been studied by electron microscopy and by quantal analysis. Earlier work has shown that the transmitter liberated by isolated Retzius cells, serotonin, evokes chloride‐dependent inhibitory post‐synaptic potentials (i.p.s.p.s) in P sensory cells, and also in Retzius cells. When pairs of Retzius cells or Retzius and P sensory cells were placed in close apposition in culture for a few days, their somata extended numerous fine processes which came into contact and interdigitated. In the region of interdigitation, only narrow spaces, approximately 20‐25 nm wide separated the membranes. The appearance of the cytoplasm of the two neurones was distinctive: in particular, Retzius cells contained agranular vesicles, as well as abundant dense core vesicles which were not as prevalent in P cells. Structures resembling synapses developed by 4 days, with characteristic vesicles clustered in terminals of the Retzius cell apposed to the post‐synaptic membrane. In the presence of raised Mg or lowered Ca in the culture medium, the i.p.s.p. in the P cell evoked by an impulse in the Retzius cell became diminished in amplitude. The time‐to‐peak and half‐time of decay were unchanged. Under these conditions, with repeated stimulation, quantal fluctuations of these post‐synaptic potentials and failures were observed. In addition, there occurred spontaneous events which resembled miniature synaptic potentials and had amplitudes and time courses similar to those of the unitary events evoked by presynaptic impulses. The amplitudes of evoked synaptic potentials in raised Mg were distributed in accord with the Poisson equation. The agreement was good when either the spontaneous miniature potentials or the failures of evoked release were used to calculate m, the mean number of quanta per trial. With larger values of m the results were distributed as predicted by the binomial equation. These morphological and electrophysiological experiments together indicate that the inhibitory potentials observed in P cells result from quantal units of transmitter released by presynaptic terminals of the Retzius cell which are in close apposition to the post‐synaptic membrane.
Selective reinnervation of twitch and tonic muscle fibres of the frog.
Authors: Elizalde A , Huerta M , Stefani E
Published: December 2014

The electrical properties and innervation of piriformis muscle fibres and the conduction velocities and thresholds of the corresponding motor axons were studied. In normal muscles all fibres clearly fell into the category of twitch or tonic. Tonic muscle fibres were selectively reinnervated by small motor axons after crushing or cutting the piriformis nerve. Twitch fibres were reinnervated by large motor axons. Tonic fibres were also selectively reinnervated by small motor axons when the proximal stump of the piriformis nerve was cut and attached to the caudal end of the muscle. With this procedure the possibility of mechanical guidance by remaining neural sheaths was eliminated. Polyneuronal innervation in twitch fibres in piriformis muscles of normal frogs was 4.7% and in contralateral muscles of operated frogs with the piriformis nerve cut it was 22.6%. Unexpectedly three out of seventeen tonic fibres in contralateral muscles were simultaneously innervated by both small and large motor axons. It is concluded that reinnervation is highly specific for fibre type in frog skeletal muscles.
Calcium transients studied under voltage‐clamp control in frog twitch muscle fibres
Authors: Miledi R. , Parker I. , Zhu P. H.
Published: December 2014

1. Intracellular calcium transients were recorded from frog twitch muscle fibres in response to voltage‐clamped depolarizing pulses, using arsenazo III as an intracellular calcium monitor. The object was to investigate the time‐ and voltage‐dependent characteristics of the coupling process between membrane depolarization and calcium release from the sarcoplasmic reticulum (s.r.)

2. To examine the extent to which the T‐tubule membrane potential was controlled during clamp pulses, the dye NK 2367 was used as an optical probe of tubular potential. This indicated that the tubular time constant is about 0·6 msec.

3. Strength—duration curves were obtained for depolarizing pulses required to give both threshold mechanical contraction and calcium signal. Curves measured in these two ways were closely similar.

4. Changes in holding potential altered the strength—duration curve for calcium release so that at more positive holding potentials a shorter pulse was needed to obtain a response for any given pulse amplitude.

5. A latency of a few milliseconds was observed between the onset of depolarization and the initial rise of the calcium signal. This became shorter with stronger depolarizations, but approached a minimum at potentials above about +25 mV.

6. Subthreshold depolarizations applied before a test pulse increased the size and decreased the latency of the calcium signal. Conditioning hyperpolarizations had opposite effects.

7. The rate of build‐up of potentiation or depression of response size seen with subthreshold de‐ and hyperpolarizing conditioning pulses was examined using conditioning pulses of different durations. For both pulses this process showed a time constant of about 3 msec (at 10 °C).

8. The rate of decay of potentiation or depression was similarly measured, using a gap of variable duration between conditioning and test pulses. For both de‐ and hyperpolarizing pulses this showed a time constant of about 5 msec (10 °C).

9. The relationship between conditioning pulse potential, and the size of calcium signal elicited by a following test pulse was non‐linear.

10. Subthreshold pulses immediately following a brief test pulse affected the size of the calcium signal in a similar way to preceding conditioning pulses.

11. The relationship between potential and size of the calcium signal was examined using pulses of 3 and 20 msec duration. With the long pulse the relation was roughly sigmoid, but with the short pulse continued to rise even at strongly positive potentials.

12. The results are discussed in terms of a model in which the exponential build‐up of a hypothetical coupler in the excitation—contraction (e.—c.) coupling process is presumed to lead to calcium release when a threshold level is exceeded.
Activation of potassium transport induced by secretagogues in superfused submaxillary gland segments of rat and mouse.
Authors: Katoh K , Nakasato M , Nishiyama A , Sakai M
Published: December 2014

In order to investigate the actions of acetylcholine (ACh), catecholamines and substance P on K transport in the submaxillary gland, measurements of net K flux to and from the gland tissue using flame photometry, Na efflux from the tissue using radioactive 22Na, and membrane potential and input resistance using micro‐electrodes were carried out on isolated superfused segments of rat and mouse submaxillary glands. ACh (5.5 X 10(‐8) to 5.5 X 10(‐4) M), phenylephrine (5 X 10(‐7) to 5 X 10(‐4) M) or substance P (10(‐9) to 10(‐5) M) stimulation for 5 min induced a transient K release followed by a small K uptake after the cessation of stimulation. The K release was markedly enhanced by the simultaneous addition of ouabain (10(‐3) M). On the other hand, isoprenaline (2.5 X 10(‐9) to 2.5 X 10(‐5) M) induced a transient K uptake without any preceding K release. The K uptake was completely blocked by the addition of ouabain. Noradrenaline induced only K uptake at a low concentration (3 X 10(‐7) M), but induced transient K release followed by marked K uptake at higher concentrations (3 X 10(‐6) to 3 X 10(‐4) M). The K release induced by noradrenaline was suppressed by the addition of phentolamine (10(‐5) M), while the K uptake was suppressed by propranolol (5 X 10(‐6) M). The K release induced by ACh, phenylephrine, noradrenaline or substance P was severely reduced by Ca omission from the superfusing solution and restored by the re‐admission of Ca. The isoprenaline‐ or noradrenaline‐induced K uptake was, however, little affected by Ca omission. Application of isoprenaline (2.5 X 10(‐6) M) induced an increase in 22 Na efflux. The increase in 22Na efflux was completely abolished in the presence of ouabain. Local application to the tissue bath of isoprenaline (4.7 X 10(‐13) to 4.7 X 10(‐12) mole) or noradrenaline (5.7 X 10(‐12) to 5.7 X 10(‐11) mole) in the presence of phentolamine (10(‐5) M) induced membrane hyperpolarization without any appreciable change in input resistance. The hyperpolarization was abolished in the presence of ouabain (10(‐3) M) or propranolol (5 X 10(‐6) M) or in a K‐free or low Na solution. Higher doses of both agonists, however, induced depolarization or biphasic responses (initial depolarization followed by hyperpolarization). The depolarizations were accompanied by a moderate reduction in input resistance. It is concluded that in the rat and mouse submaxillary gland acinar cells cholinergic, alpha‐adrenergic or substance P stimulation causes K release (and perhaps Na uptake) resulting in activation of the Na‐K pump, while beta‐adrenergic receptor stimulation might directly activate the Na‐K pump resulting in K uptake, or might cause Na uptake resulting in activation of the Na‐K pump.
The effects of supplementation of the diet with highly palatable foods upon energy balance in the rat.
Authors: Armitage G , Hervey G R , Rolls B J , Rowe E A , Tobin G
Published: December 2014

Full energy balance studies have been performed for 9 weeks on four groups of four adult female rats housed in a continuously running indirect calorimeter; for four weeks two of the groups received highly palatable foods in addition to a standard pelleted diet. A further sixteen groups, of which eight received the palatable foods, provided additional carcass composition data. All practicable precautions were taken to measure energy exchange accurately. Comparison of ‘start‐to‐finish’ apparent energy balance with carcass composition changes showed a systematic error of approx. +3% of energy throughput. This was most probably caused by losses of energy in food and excreta, which led to over‐estimation of energy intake. Variations among individual balance periods added a standard error of approx. +/‐ 1%: the source of error here was probably imperfect matching of animals analysed at intermediate stages. The rats offered the palatable foods increased their metabolizable energy (m.e.) intake by 106 kJ/day, 51% of the control groups’ intake, in the first week of supplementation. Over the whole 4 weeks of supplementation the increase was 64 kJ/day, or 31%. Withdrawal of the palatable foods led to an immediate fall in intake to about two‐thirds of control level, and a return to control level over the next 2‐3 weeks. Energy expenditure rose more slowly than intake, reaching a fairly steady level ca. 5 days after introduction of the palatable foods. Expenditure was then ca. 22 kJ/day above control level; an increase of 12% above control expenditure or, allowing for systematic and random errors, 33‐37% of the additional m.e. intake. Expenditure returned to control level over the 2 weeks after ceasing supplementation. The experimental groups gained weight at a declining rate throughout the period of supplementation. The gain in live body weight at the end was ca. 32 g, but this comprised a carcass weight gain of 37 g and a loss of 5 g gastrointestinal tract contents. The carcass weight gain comprised 27 g fat (i.e. ca. 70% of the weight gained), 9 g lean tissue and 1 g additional water. The gain of carcass energy was 1100 kJ. There was a small increase in body length, an increase in liver weight, and an increase in the weight of the interscapular brown adipose tissue pad. Regression analysis showed that the increase in the weight of the interscapular brown adipose tissue pad reflected the increase in total body fat.(ABSTRACT TRUNCATED AT 400 WORDS)
The action of dust in the airways on secretion into the trachea of the cat.
Authors: Peatfield A C , Richardson P S
Published: December 2014

The effects of inert dusts administered into cat airways on the release of radiolabelled mucus glycoproteins (mucins) from an isolated tracheal segment have been investigated. Charcoal dust or barium sulphate powder, when placed in the segment, stimulated release of both 35S‐ and 3H‐labelled mucins. The effect of dust was not significantly reduced after denervation of the segment. Charcoal dust, when added to the inspired air, caused an increase in release of mucins labelled with both radio‐isotopes. Bilateral vagotomy significantly reduced this effect, but atropine and l‐propranolol administered together did not. It is concluded that inert dust can stimulate tracheal mucin output both by a local mechanism and by activation of a reflex. The types of receptor that may be involved in the reflex, and the possible role of the mucotropic effects of dust in airway clearance, are discussed.
Physiological characteristics of single green rod photoreceptors from toad retina.
Authors: Matthews G
Published: December 2014

The outer segment membrane current of single isolated green and red rods from toad retina was recorded with a suction electrode, and characteristics of the response to light were examined. The maximum response amplitude of green rods was smaller than that of red rods, but the density of dark current along the green rod outer segment was similar to previously reported values for red rods. Thus, the smaller maximum response is explained by the shorter outer segment of green rods (45 vs. 60 microns). The intensity‐response relation was fitted by a Michaelis equation with half‐saturating photon density corresponding to about 55 isomerizations per flash. The form of the green rod light response was similar to that of red rods: in both cases the kinetics were consistent with four first‐order delay stages shaping the light response. The time‐to‐peak of the dim‐flash response was usually about 1 sec for both green and red rods in the present experiments. The spectral sensitivity curve of green rods was fitted by the nomogram for a vitamin A1‐based pigment with lambda max = 433 nm. The relation between steady light intensity and flash sensitivity of green rods obeyed the Weber‐Fechner relation, and the average background intensity necessary to reduce sensitivity to half of its dark level corresponded to about 4 isomerizations sec‐1. This is slightly lower than the value of about 8 isomerizations sec‐1 reported for toad red rods by Baylor, Matthews & Yau (1980). Green rods were similar to red rods in all respects except spectral sensitivity. Thus, no evidence was found to support the assertion that green rods are ‘cone‐like'.
The permeability of rabbit and human corneal endothelium.
Authors: Hodson S , Wigham C
Published: December 2014

The fluxes of sodium, chloride and bicarbonate across endothelium plus stroma and then stroma alone were measured in the direction from lens‐side to tear‐side in rabbit and human corneas in vitro, in order to measure passive permeabilities. The results were used to calculate the permeability of the endothelium. Hodgkin's equation (1951) was then used to calculate the partial electrical conductivity of each ion crossing the endothelium. The summated electrical conductivities of sodium, chloride and bicarbonate were equal to 89 +/‐ 8% of the measured electrical conductivity, suggesting that the ions diffuse independently across the endothelium in the direction lens‐side to tear‐side. Stereological analysis of the intercellular spaces supports the idea that the ions permeate through this route and that the physical shape of the spaces determines almost entirely the permeability of the endothelial layer. Trans‐endothelial sodium and chloride permeabilities are nearly equal, which may be explained by supposing the intercellular spaces include a cation exchanger of fixed negative charge capacity around 60 m‐equiv l.‐1 intercellular fluid.
Kinetics of inward rectifier gating in the eggs of the marine polychaete, Neanthes arenaceodentata.
Authors: Gunning R
Published: December 2014

Potassium current through the inward rectifier of Neanthes arenaceodentata eggs was studied using a voltage‐clamp technique. The instantaneous conductance, steady‐state conductance and the time constant of current relaxation were analysed as functions of the membrane potential and the external potassium concentration ([K]o). Both the instantaneous and the steady‐state conductances increased sigmoidally with hyperpolarization, reaching saturation values at potentials 40 mV more negative than the potassium equilibrium potential (EK). The time‐dependent change in conductance followed first‐order kinetics throughout an 80 mV potential range centred at EK. The conductances increased with time during hyperpolarizations and decreased with time during depolarizations. The time constant decreased sigmoidally about EK as the membrane potential (Vm) was made more positive. The results are interpreted in terms of two models. The first model assumes single‐channel rectification. Forcing the data to conform with this assumption necessitates that the single‐channel conductance, the open‐channel probability, and the time constant of current relaxation all be nearly identical functions of Vm‐‐EK. This coincidence is considered implausible. The second model ascribes the apparent instantaneous rectification to a fast kinetic process. This model correctly predicts the steady‐state conductance, the time‐constant of current relaxation, and the unexpected proportionality between the ratio of the steady‐state and ‘instantaneous’ conductances and the time constant of current relaxation. This agreement between data and model is obtained even though neither of the rate constants of the slow gating process has the flexibility of voltage or potassium dependence. The results are considered to imply the existence of a fast gating mechanism in the kinetics of inward rectification.
The activity of cerebellar nuclear neurones in relation to stimuli which evoke a pectoral fin reflex in dogfish.
Authors: Paul D H , Roberts B L
Published: December 2014

Extracellular single‐unit recordings from the cerebellar nucleus were classified into type I and type II units on the basis of their spontaneous discharges. Type I units discharged at a very regular frequency, giving interspike interval histograms with narrow distributions. Type II units had irregular discharges. Type I units were identified as cerebellar nuclear units by their antidromic responses to stimulation of the contralateral brachium conjunctivum (b.c.) in the mid‐brain and by their inhibitory responses to stimulation of the cerebellar cortex. Type II units were not driven antidromically by b.c. stimulation but were inhibited by stimulating the cerebellar cortex. Activity of the nuclear neurones was monitored following subcutaneous electrical stimulation of a fin that elicits a reflex elevation. 67% of units responded, the majority with an increased discharge frequency (excitation, 59%) but some with a decreased discharge frequency ('inhibition', 8%). Latencies of both excitatory and inhibitory responses were greater than 50‐400 msec. Most excitatory responses lasted for at least 500 msec; several lasted for more than 10 sec. Inhibitory responses lasted for about 500 msec. With units tested by bilateral fin stimulation, the same qualitative response was obtained whichever fin was stimulated. These results are discussed in relation to the known responses of cerebellar Purkinje cells recorded under similar experimental conditions.
Membrane properties of cat sensory neurones with chemoreceptor and baroreceptor endings.
Authors: Belmonte C , Gallego R
Published: December 2014

The properties of chemoreceptor and baroreceptor neurones in the petrosal ganglion of the cat were examined in vitro with intracellular micro‐electrodes. Chemoreceptor neurones with myelinated axons (average conduction velocity, 11 m/s) showed action potentials with a hump on the falling phase, followed by a prolonged after‐hyperpolarization (average duration, 260 ms). The duration of the hump present in the action potential of chemoreceptor neurones was positively correlated with the duration of the after‐hyperpolarization. In response to prolonged depolarization, chemoreceptor neurones showed only one or a few action potentials at the beginning of the depolarization. Two types of baroreceptors neurones with myelinated axons were found: fast (F) baroreceptors (average conduction velocity, 33 m/s) and slow (S) baroreceptors (average conduction velocity, 10 m/s). F baroreceptors had action potentials without a hump followed by a short after‐hyperpolarization (average duration, 43 ms), while S baroreceptors had spikes similar to those found in chemoreceptors except for a shorter hyperpolarization (average duration, 145 ms). Both types of baroreceptor neurones fired repetitively throughout prolonged depolarization. It is concluded that, in the petrosal ganglion, primary sensory neurones originating a given type of sensory terminal share a particular set of electrophysiological properties.
The synaptic current evoked in cat spinal motoneurones by impulses in single group 1a axons.
Authors: Finkel A S , Redman S J
Published: December 2014

Excitatory post‐synaptic potentials (e.p.s.p.s) were evoked in motoneurones of anaesthetized cats by impulses in single group 1 a axons. E.p.s.p.s with a time course which indicated a somatic site of origin were voltage‐clamped using a single micro‐electrode clamp. Excitatory post‐synaptic currents (e.p.s.c.s) were found to peak in less than 0.2 ms, and to decay with an exponential time course. The time constant of decay was usually in the range 0.3‐0.4 ms (at 37 degrees C). At the resting membrane potential, an e.p.s.p. with a peak of 100 microV was generated by an average peak e.p.s.c. of 330 pA. This corresponded to an average peak conductance increase of 5 nS. The e.p.s.c. decreased with membrane depolarization, and reversed to become an outward current at a null potential of +4.6 +/‐ 2 mV (+/‐ S.E. of mean; n = 7). Membrane hyperpolarization caused the peak e.p.s.c. to increase and the time constant of decay of the e.p.s.c. to decrease. The total charge in the synaptic current did not increase with hyperpolarization. This observation can explain earlier observations which showed that the peak amplitude of the e.p.s.p. did not increase with hyperpolarization. The number of ion channels opened by transmitter release at a single somatic bouton was estimated to be in the range 40‐240.