bluuebunny/crossref_metadata_2025 huggingface dataset:
Slow non‐cholinergic excitatory potentials in neurones of the guinea‐pig coeliac ganglia.
Authors: Dun N J , Ma R C
Published: December 2014

Intracellular recordings were made from neurones of the coeliac ganglia of the guinea‐pig in vitro. In addition to the fast excitatory post‐synaptic potential (e.p.s.p.) repetitive stimulation (10‐20 Hz, 1‐2 s) of the left greater splanchnic nerves elicited a slow depolarization in about 70% of the neurones examined. This depolarization lasted for minutes and was resistant to nicotinic and muscarinic antagonists; it was abolished reversibly in a low‐Ca2+, high‐Mg2+ solution. The response is henceforth termed non‐cholinergic e.p.s.p. In about 10% of the neurones the non‐cholinergic e.p.s.p. exhibited a biphasic pattern. The fast as well as the non‐cholinergic e.p.s.p. could be effectively induced by stimulation of any of the several nerve trunks that enter the ganglion. Moreover, simultaneous stimulation of two separate nerves resulted in a much larger non‐cholinergic e.p.s.p. than could be achieved by stimulation of a single nerve. When the membrane potential was manually clamped, the non‐cholinergic e.p.s.p. was associated with an increase of membrane resistance in the large majority of cells tested. Membrane hyperpolarization generally caused an increase in the amplitude of the non‐cholinergic e.p.s.p.; a decrease was observed in only a few cells. Subthreshold depolarizations induced by direct intracellular stimulation as well as fast e.p.s.p.s elicited by heterosynaptic nerve stimulation were facilitated during the course of a non‐cholinergic e.p.s.p., often resulting in spike discharges. A potentiation of lesser magnitude occurred when the membrane potential was manually clamped during the course of the slow response, indicating that the facilitation may be attributed to both membrane depolarization and increased membrane resistance. These results indicate that the non‐cholinergic e.p.s.p. constitutes an integral part of synaptic transmission in coeliac ganglia, and that its function may be to provide a mechanism for increasing the responsiveness of sympathetic neurones to incoming fast e.p.s.p.s.
Evidence for a serotonin‐mediated slow excitatory potential in the guinea‐pig coeliac ganglia.
Authors: Dun N J , Kiraly M , Ma R C
Published: December 2014

The nature of the putative transmitter(s) mediating the non‐cholinergic excitatory post‐synaptic potential (e.p.s.p.) described in the preceding paper was investigated by means of electrophysiological, pharmacological and immunohistochemical methods. Serotonin (1‐10 microM) when applied by superfusion caused a slow depolarization that closely mimicked the synaptic response in about 60% of the coeliac neurones that exhibited a non‐cholinergic e.p.s.p. The serotonin depolarization evoked in low‐Ca2+, high‐Mg2+ solution or in a Krebs solution containing cholinergic antagonists was quantitatively similar to that elicited in normal Krebs solution. When compared in the same neurones the membrane resistance change during the course of the serotonin depolarization and of the non‐cholinergic e.p.s.p., as well as their respective responses to conditioning polarization, were similar. The non‐cholinergic e.p.s.p. was reversibly abolished during serotonin‐induced depolarization; the blockade persisted when the membrane potential was restored to the resting level by hyperpolarizing current. The serotonin depolarization as well as the non‐cholinergic e.p.s.p. were reversibly suppressed by cyproheptadine (20‐50 microM), a serotonin antagonist, and enhanced by fluoxetine (30‐50 microM), a serotonin reuptake inhibitor. On the other hand, pre‐treating the ganglia with L‐tryptophan (50 microM), a precursor of serotonin, preferentially augmented the synaptically induced response. A portion of the neurones (15%) were depolarized by substance P (1 microM) which also reversibly desensitized the non‐cholinergic e.p.s.p. elicited in these neurones. The remaining neurones (25%) were insensitive to either serotonin or substance P, and the non‐cholinergic e.p.s.p.s elicited in these cells were likewise not appreciably affected by these two agents. Furthermore, cyproheptadine, fluoxetine and L‐tryptophan had no significant effect on the non‐cholinergic e.p.s.p.s elicited in serotonin‐insensitive neurones. Using the immunohistofluorescent techniques, dense but unevenly distributed serotonin immunoreactive nerve fibres could be observed surrounding many coeliac neurones. Immunoreactivity was not observed in the ganglia incubated with antisera pre‐absorbed with excess serotonin. Collectively our results suggest that serotonin is the mediator of non‐cholinergic e.p.s.p.s. elicited in about 60% of coeliac neurones sampled in this study, and that in the remaining neurones the slow depolarization may be generated by substance P and/or some unknown transmitter(s).
Stimulus‐specific patterns of intracellular calcium levels in smooth muscle of ferret portal vein.
Authors: Morgan J P , Morgan K G
Published: December 2014

Aequorin was loaded into cells of the ferret portal vein in order to follow intracellular Ca2+ levels during smooth muscle contraction. In response to a single d.c. pulse, the aequorin signal reaches a peak during the rising phase of the evoked force transient and begins to rapidly fall while force is still rising. In response to the addition of phenylephrine to the bathing solution, the aequorin signal rises rapidly to a peak while force is still rising but then falls rapidly to a lower level from which it declines more slowly, staying above base‐line levels as long as force is maintained. In response to the elevation of K+ concentration in the bathing solution, light and force rise together and the elevated light level is maintained as long as is force. With increasing concentrations of K+, force increases up to a concentration of 50‐60 mM but light increases up to 90 mM, suggesting that at a concentration of 50‐60 mM‐K+, the Ca2+ concentration may be saturating with respect to a site of action on the contractile apparatus. During the period of force maintenance, phenylephrine produces a larger ratio of force to light than does K+ depolarization. The maintenance of force in the presence of either phenylephrine or elevated K+ requires an elevation of intracellular Ca2+ levels above base‐line values. These results suggest that phenylephrine can increase the effectiveness of Ca2+ on the contractile apparatus.
Electrophysiology and enkephalin immunoreactivity of identified myenteric plexus neurones of guinea‐pig small intestine.
Authors: Bornstein J C , Costa M , Furness J B , Lees G M
Published: December 2014

Intracellular injection of the fluorescent dye, Lucifer Yellow CH, revealed the shapes of neurones in the myenteric plexus of the guinea‐pig ileum, and these shapes were correlated with the electrophysiological properties and enkephalin immunoreactivity of the neurones. A total of eighty‐three neurones were filled using electrodes containing a 5% solution of the dye. Forty‐six cells had many short processes and a single long process (Dogiel type 1) and twenty‐four cells had essentially smooth somas and one to eight long processes (Dogiel type II). Thirteen cells could not be put into either group. Enkephalin‐like immunoreactivity was detected in twenty‐two of the forty‐six Dogiel type I cells. Eighteen of these had club‐like short processes. No other cells of the eighty‐three showed enkephalin‐like immunoreactivity. Electrodes filled with a 0.5% solution of Lucifer Yellow in 0.5 M‐KCl were used to record from and simultaneously to inject dye into 240 neurones. Eighty‐six nerve cells had a slow after‐hyperpolarization following the action potential (AH cells) and forty‐six nerve cells had no after‐hyperpolarization but exhibited a fast excitatory synaptic potential (S cells). The other cells could not be unequivocally identified by their observed electrophysiological characteristics. Almost all S cells (forty‐two of forty‐six) were Dogiel type I, while eighty‐two of the eighty‐six AH cells were Dogiel type II. Fifty S cells (eight located geometrically, forty‐two by dye injection) and ninety‐one AH cells (twenty‐six located geometrically, sixty‐five by dye injection) were examined for enkephalin immunoreactivity. Fifteen of the S cells were reactive, whereas all of the AH cells were unreactive. It appears that prolonged impalements reduce immunoreactivity so that the proportion of reactive neurones in this series is an underestimate of the true proportion of S cells with enkephalin‐like immunoreactivity. The results suggest that a substantial proportion of the S cells in myenteric ganglia contain enkephalin immunoreactivity while none of the AH cells do. The enkephalin neurones have a distinctive shape and are all Dogiel type I cells. AH cells are nearly always Dogiel type II.
Discharges of nucleus interpositus neurones during locomotion in the cat.
Authors: Armstrong D M , Edgley S A
Published: December 2014

Extracellular recordings were made from ninety‐five cerebellar nuclear neurones in the cat. All were studied during periods of steady walking at 0.5 m/s and most were also studied in the resting animal. Most neurones were in nucleus interpositus anterior; forty‐four cells were shown by antidromic invasion to project to the mid‐brain. Most neurones discharged tonically in the absence of overt movements and the mean rate was 42 impulses/s (S.D. +/‐ 23). During locomotion the mean rate was 68 impulses/s (S.D. +/‐ 32). In all but seven neurones the discharge during locomotion was frequency modulated but in different neurones the depth of modulation varied from 5 to 161 impulses/s (mean 52 impulses/s; S.D. +/‐ 30) and the time of peak discharge relative to the step cycle in the ipsilateral forelimb also varied widely. Despite the individual differences the population as a whole was much more active during forelimb swing than during stance, both in numbers of neurones strongly active and in over‐all average discharge rate (74 impulses/s as compared with 55). Most neurones had tactile receptive fields on the ipsilateral forelimb while others received input from head and neck or from both ipsilateral limbs. The tendency to discharge preferentially during early swing was greatest for the first group, especially the subpopulations with receptive fields around or proximal to the elbow. Cells encountered in close sequence during a micro‐electrode track had similarly located receptive fields and usually showed similar patterns of discharge during locomotion. These findings are discussed in relation to the suggestion by Orlovsky (1972a, b, c) that nucleus interpositus assists in regulating locomotion by evoking rubrospinal discharges which facilitate the flexor muscle activities produced by the spinal mechanisms responsible for generating the swing phase of the step cycle.
Analysis and interpretation of turning points and run lengths in breath‐by‐breath ventilatory variables.
Authors: Bolton D P , Marsh J
Published: December 2014

Three healthy young male volunteers were studied for 10 min periods of steady‐state ventilation under the following conditions: air breathing, 50% inspired oxygen, hyperoxic hypercapnia and hypoxic hypercapnia. Eight variables were recorded breath‐by‐breath: inspiratory and expiratory tidal volumes, mean flows and durations, total breath duration and expiratory ventilation. Each resulting sequence of breath‐by‐breath data was analysed in terms of the number of 'turning points' in the sequence and the concomitant mean 'run length' between turning points. The mean run length for all these variables was 1.600, 1.599 and 1.592 in the three subjects. These values are significantly greater than the expected value of 1.5 for random data sequences. There were no consistent significant differences between variables or subjects. Under conditions of hypoxic hypocapnia the mean run length of all variables was found to be 1.666, 1.724 and 1.568 in the three subjects. The two higher values corresponded with periodic breathing of period 10‐30 s. These observations are lower than previously published values. A number of ways of interpreting a mean run length of greater than 1.5 are suggested.
Drinking and renal responses to peripherally administered osmotic stimuli in the pigeon (Columbia livia).
Authors: Thornton S N
Published: December 2014

Pigeons drank copiously in response to intravenous (I.V.) infusion of approximately equi‐osmolar hypertonic solutions of NaCl (0.5 M), sucrose (1.0 M) or mannitol (1.0 M). I.V. infusions of hypertonic glucose (1.0 M) or urea (1.0 M) were less effective in causing drinking. The calculated percentage change in plasma osmolality at the onset of drinking was similar for the three hypertonic solutions, NaCl, sucrose and mannitol, irrespective of the concentration of the solution infused. A greater volume of water was drunk in response to I.V. infusion of 7 ml of 1.0 M‐sucrose than in response to a similar volume of 1.0 M‐NaCl or mannitol. This appeared to be in response to the large diuresis caused by sucrose infusions. Excretion of the osmotic load was more rapid following I.V. hypertonic sucrose and mannitol than following hypertonic NaCl, glucose or urea in the 10 h of the experiment. In anaesthetized pigeons, I.V. infusion of hypertonic NaCl (0.5 M), sucrose (1.0 M) or urea (1.0 M) caused similar increases in plasma osmolality. The haematocrit was significantly reduced after NaCl or sucrose but not after urea. Plasma Na+ concentration was significantly increased after NaCl, and decreased after sucrose, whereas urea produced little change. Following I.V. hypertonic NaCl or urea, the Na+ concentration of the cerebrospinal fluid (c.s.f.) was increased and its flow reduced compared with isotonic NaCl infusions. Hypertonic sucrose stopped the flow of c.s.f. almost completely during the course of the experiment. These experiments suggest that the drinking and renal responses of pigeons following osmotic stimuli are similar to those of mammals and that they appear to retain Na+.
The effect of chloride removal on the responses of the isolated rat anococcygeus muscle to alpha 1‐adrenoceptor stimulation.
Authors: Large W A
Published: December 2014

The effect of Cl removal on the depolarizations and contractions produced by activation of the alpha 1‐adrenoceptor in the isolated rat anococcygeus was studied. In normal Krebs solution the ionophoretic application of noradrenaline and phenylephrine elicited large depolarizations; when NaCl was replaced with Na benzenesulphonate application of the agonists usually evoked no membrane response but sometimes a hyperpolarization or a biphasic membrane potential change was observed. Graded replacement of Cl by benzenesulphonate produced a progressive reduction in the depolarizing ability of noradrenaline and phenylephrine. When NaCl was replaced with Na isethionate or glucuronate, noradrenaline evoked small depolarizations in most of the cells but the sensitivity to noradrenaline (mV/nC) was reduced by over 80%. In other cells either no potential change or hyperpolarization was observed. In solutions containing low Cl the resting membrane potential was slightly depolarized by a mean value of 5‐10 mV (depending on the anion substitute) and the membrane resistance was unaltered. In normal Krebs solution noradrenaline and phenylephrine evoked biphasic contractile responses but when NaCl was replaced by Na benzenesulphonate the initial rapid contraction was diminished greatly or abolished. However, the maximum tension produced by any concentration of noradrenaline was unaltered in low Cl solution although the contractions produced by phenylephrine were depressed in low Cl media. These data are further evidence that stimulation of the alpha 1‐adrenoceptor in smooth muscle can produce contraction which is not mediated by a change in membrane potential.
Characterization of oscillations of intracellular calcium concentration in ferret ventricular muscle.
Authors: Allen D G , Eisner D A , Orchard C H
Published: December 2014

The photoprotein aequorin was injected into superficial cells of ferret papillary muscles. Tension and aequorin light (a function of intracellular [Ca2+]) were monitored. Increasing intracellular Ca concentration ([Ca2+]i), either by decreasing extracellular Na, or by inhibiting the Na pump with strophanthidin, produced spontaneous oscillations of [Ca2+]i and tension. Fourier analysis showed that these oscillations had frequencies of up to 3‐4 Hz. If the muscle was stimulated in these conditions the Ca transient associated with the twitch was followed by a series of damped oscillations of [Ca2+]i which were accompanied by after‐contractions. Under a given set of conditions the frequency of the stimulated oscillations was similar to that of the spontaneous oscillations. Manoeuvres which increase [Ca2+]i increased the frequency of both spontaneous and stimulated oscillations. Drugs which inhibit the function of the sarcoplasmic reticulum (caffeine and ryanodine) abolished both stimulated and spontaneous oscillations. The spontaneous oscillations during a Na‐free contracture were unaffected by the Ca channel blocker D‐600. When repetitive stimulation was begun the frequency and magnitude of the stimulated oscillations increased over several minutes. Increasing the frequency of stimulation increased the magnitude of the stimulated oscillations. It is concluded that the spontaneous oscillations of [Ca2+]i may be due to oscillatory Ca release from the sarcoplasmic reticulum. The similar properties of the spontaneous and stimulated oscillations suggest that the latter may be due to a synchronization of the former.
Cat ventricular muscle treated with D600: characteristics of calcium channel block and unblock.
Authors: McDonald T F , Pelzer D , Trautwein W
Published: December 2014

Thin preparations of cat ventricular muscle were mounted in a single sucrose gap and superfused with Tyrode solution containing 1‐5 microM‐D600. In voltage‐clamp experiments lasting for 40‐180 min, stimulation with standard pulses (‐50 to 0 mV, 300 ms) at 0.33 Hz depressed Ca‐dependent slow inward current (ICa) to less than 20% of its pre‐drug amplitude. A reproducible unblocking of ca. 75% of the blocked Ca channels could be achieved with a single hyperpolarizing pulse (90 s at ‐90 mV); stimulation (conditioning) at 0.33 Hz re‐established full block within thirty pulses. The time and voltage dependence of block and unblock were examined by varying the frequency and duration of voltage‐clamp pulses. The time course of unblock was usually monoexponential. The time constant was voltage dependent and declined from 9 min at ‐50 mV to 5 s at ‐110 mV. Block appears to depend on channel state, resting channels being highly resistant to block and open channels very susceptible. D600 also binds to inactivated channels but at a much slower rate than to open channels. A small U‐shaped component of block was induced by conditioning to potentials between +10 and +80 mV. This block seemed to be unrelated to channel state, suggesting that drug binding may also be dependent on voltage. Quicker rates of block after repetitive conditioning, and slow wash‐out of the drug, may indicate the existence of an intramembrane drug pool distinct from the primary pool in the intracellular fluid. The interaction of D600 with Ca channels is discussed in terms of a channel state model. In many respects this interaction resembles that of local anaesthetics with Na channels.
The inhibitory effects of monovalent ions on force development in detergent‐skinned ventricular muscle from guinea‐pig.
Authors: Kentish J C
Published: December 2014

Trabeculae from guinea‐pig ventricles were bathed in a physiological saline, were stimulated electrically and were stretched until isometric force production was maximal. They were then 'skinned' by superfusion for 30 min with a solution containing the non‐ionic detergent, Triton X‐100. The steady isometric force generated by these skinned trabeculae was measured in solutions of different pCa (‐log10 [Ca2+]) and salt concentration to investigate the influence of salt concentration on (i) the maximum Ca2+‐regulated force (at pCa approximately 3.8), (ii) the resting force (at pCa greater than 8) and (iii) the pCa required for 50% Ca2+ activation (pCa50). The apparent affinity constants of EGTA (ethyleneglycol‐bis‐(beta‐aminoethylether)‐N,N,N',N'‐tetraacetic acid) for Ca2+ were measured in the solutions of different salt composition by a pH‐metric method and these constants were used in the calculation of solution pCa. Increases in ionic strength (gamma/2) (and osmolarity) over the range 0.1‐0.4 mol/l produced by the addition of various monovalent Cl or K salts resulted in an approximately linear decrease in the maximum Ca2+‐regulated force. The inhibitory actions of the different salts were similar despite the differences in size and structure of their constituent ions. Increases in solution osmolarity alone, produced by the addition of sucrose up to 0.6 mol/l, did not significantly alter the maximum Ca2+‐regulated force. It was concluded that the influence of monovalent salts on the maximum Ca2+‐regulated force was due entirely to the changes in ionic strength and was not related to changes in solution osmolarity or to specific ion effects. Resting force was little affected by changes in salt concentration at ionic strengths of 0.2 mol/l and above. At lower ionic strengths the muscles exhibited an elevated resting force and an inability to relax completely after a Ca2+ ‐regulated contracture. A decrease in ionic strength from 0.2 to 0.1 mol/l produced by a reduction in KCl concentration raised the pCa50 from 5.56 to 5.85, i.e. the Ca2+ sensitivity was increased. However, the same increase in pCa50 was observed when the [K+] was lowered at constant ionic strength, osmolarity and [Cl‐] by the replacement of KCl with tetramethylammonium Cl or choline Cl. Therefore, the change in pCa50 induced by an alteration in KCl concentration was due entirely to a specific inhibitory action of K+ on the Ca2+ sensitivity of cardiac myofibrils and was unrelated to changes in ionic strength, osmolarity and [Cl‐]. Substitution of KCl 0.1 mol/l in the solutions by NaCl did not significantly alter the pCa50.(ABSTRACT TRUNCATED AT 400 WORDS)
Release of hydrolases and acetylcholine sensitivity in rat skeletal muscle.
Authors: Harborne A J , Shute J K , Smith M E
Published: December 2014

Cytosol prepared from the hind‐limb muscles of the rat contained factors which increased the acetylcholine (ACh) contractures in intact normally innervated muscles in vitro. Muscles which had been denervated 4‐6 days previously and normally innervated muscles released a factor upon incubation which increased the ACh responses of normal muscles. The normal muscles, however, also released an inhibitor of this effect. The medium obtained after incubation of the muscles contained a variety of hydrolytic enzymes including phospholipase C, acid protease and calcium‐activated neutral protease. The amounts of phospholipase C released by normal and denervated muscles were similar, but approximately four times more of the two proteases was released from the denervated muscles than from normal muscles. The possibility that these hydrolases could be the factors which increased the ACh sensitivity in normal muscles is discussed.
Rearrangement of neuronal responses in the trigeminal system of the rat following peripheral nerve section.
Authors: Waite P M
Published: December 2014

The infraorbital nerve was cut in either neonatal (on day 0) or adult (day 60) rats and the peripheral regeneration prevented. After 60 days either anatomical or electrophysiological techniques were used to study the peripheral nerve, trigeminal nucleus and somatosensory cortex. In neonatally sectioned animals the number of myelinated fibres surviving, at 60 days, in the peripheral nerve proximal to the lesion was 11% compared with 100% survival after adult nerve section. This reduction in surviving nerve fibres in neonatally lesioned animals was associated with a significant reduction in cross‐sectional area of all trigeminal nuclei (principalis, oralis, interpolaris and caudalis) of 18‐29%. No significant change in area was present in animals sectioned as adults. Neonatally lesioned animals also showed a reduction of approximately 20% in the number of cells visible in cross‐sections of all trigeminal nuclei. Animals sectioned as neonates showed marked plasticity at all nuclei in the trigeminal complex as well as in the cortex. Deafferented cells responded to new peripheral receptive fields so that the somatotopic organization of these cells was modified. Such cells are referred to throughout as 'reactivated' cells. However, in animals sectioned as adults no evidence of plasticity could be detected in the trigeminal nuclei. Only very limited reactivation was apparent in the cortex, so that the majority of deafferented cells remained unresponsive at both sites. A detailed comparison was made of twenty‐three reactivated cells and twenty‐five normal cells from nucleus principalis of animals with nerve section on day 0. The reactivated cells commonly showed larger, more complex receptive fields, longer latencies and lower following frequencies, although stimulus thresholds were similar. Thus reactivated cells showed more convergence and poorer synaptic security than normal cells. However, stimulation of the contralateral thalamus produced similar responses from both groups of cells, suggesting that not all inputs to reactivated cells were modified. The time course of the reactivation of cells in nucleus caudalis from animals lesioned on day 0 was followed over 30 days. No acute effect, for up to 24 h, was detected. However, somatotopic reorganization had started by day 7, proceeded rapidly between days 7 and 14, and was completed by day 21.
Increased sodium appetite and polydipsia induced by partial aortic occlusion in the rat.
Authors: Costales M , Fitzsimons J T , Vijande M
Published: December 2014

Partly occluding the abdominal aorta between the renal arteries caused the rat to drink steadily increasing amounts of 2.7% NaCl when this solution and water were available. The increase in NaCl intake preceded the increase in water intake that also occurred after aortic occlusion, and intakes of both fluids were reaching maximal values 1‐2 weeks after operation. The amounts of fluid drunk during the day increased greatly. This change in the pattern of drinking, together with the rise in fluid intake and the drop in food intake meant that drinking was less associated with feeding than it is in the normal rat. The rats went into fluid and electrolyte deficit within 24 h of partial aortic occlusion and remained in deficit for about a week (the duration of the balance experiment) despite increasing intakes of NaCl and water. Renal function was unimpaired during the first 2 weeks, and the abnormal signs were mainly and rapidly reversed by removal of the ischaemic kidney or administration of the angiotensin converting enzyme inhibitor, captopril. Therefore polydipsia and increased sodium appetite in the first 2 weeks after aortic occlusion were likely to have been caused by fluid deficit, with increased renin secretion from the ischaemic kidney contributing to both behaviours. Arterial blood pressure rose immediately after aortic occlusion, before the onset of increased drinking. Up to 3 weeks after operation the incidence and severity of the hypertension did not appear to depend on the spontaneous changes in intake of water or hypertonic NaCl.
Natriuretic response of the rat to plasma concentrations of arginine vasopressin within the physiological range.
Authors: Balment R J , Brimble M J , Forsling M L , Musabayane C T
Published: December 2014

The relationship of plasma vasopressin concentrations in the physiological range to renal electrolyte excretion was investigated. Unanaesthetized rats, when normally hydrated, were found to have a plasma vasopressin concentration of 1.13 +/‐ 0.15 mu u./ml. 16 h water deprivation raised this to 1.98 +/‐ 0.21 mu u./ml. Inactin‐anaesthetized rats infused with 0.45% NaCl had a plasma vasopressin concentration of 1.19 +/‐ 0.18 mu u./ml. Administration of synthetic arginine vasopressin at 6 and 24 mu u./min raised plasma vasopressin levels to 1.88 +/‐ 0.17 and 4.26 +/‐ 0.43 microunits./ml respectively. In addition to the expected antidiuresis, vasopressin at a rate of 6 microunits./min also produced a highly significant increase in Na+ excretion from 8.9 +/‐ 0.6 to 10.5 +/‐ 0.6 mumol/min and Cl‐ excretion from 9.1 +/‐ 0.7 to 10.5 +/‐ 0.7 mumol/min. At 24 microunits./min it produced larger increases in Na+ and Cl‐ excretion. Inactin‐anaesthetized hypophysectomized rats infused with 0.45% NaCl had a plasma vasopressin concentration of only 0.17 +/‐ 0.04 microunits./ml. Administration of vasopressin at 6 and 24 microunits./ml raised plasma vasopressin levels in these animals to 0.63 +/‐ 0.17 and 2.20 +/‐ 0.11 microunits./ml respectively. Hypophysectomized rats failed to exhibit a natriuresis in response to the lower dose of vasopressin, despite exhibiting an undiminished antidiuresis. The failure of the natriuresis may be related to the lower plasma vasopressin concentration achieved. It is concluded that in the rat plasma vasopressin concentrations within the physiological range do influence Na+ and Cl‐ excretion by the kidney as well as controlling urine flow rate.
The subtype of alpha‐adrenoceptor involved in the neural control of renal tubular sodium reabsorption in the rabbit.
Authors: Hesse I F , Johns E J
Published: December 2014

A study was undertaken in pentobarbitone anaesthetized rabbits, undergoing a saline diuresis, to determine the subtype of alpha‐adrenoceptor mediating renal tubular sodium reabsorption. Stimulation of the renal nerves at low rates, to cause an 11% fall in renal blood flow, did not change glomerular filtration rate but significantly reduced urine flow rate, and absolute and fractional sodium excretions by approximately 40%. These responses were reproducible in different groups of animals and with time. Renal nerve stimulation during an intra‐renal arterial infusion of prazosin, to block alpha 1‐adrenoceptors, had no effect on the renal haemodynamic response but completely abolished the reductions in urine flow rate, and absolute and fractional sodium excretion. During intra‐renal arterial infusion of yohimbine, to block renal alpha 2‐adrenoceptors, stimulation of the renal nerves to cause similar renal haemodynamic changes resulted in significantly larger reductions in urine flow rate, and absolute and fractional sodium excretion of about 52‐58%. These results indicate that in the rabbit alpha 1‐adrenoceptors are present on the renal tubules, which mediate the increase in sodium reabsorption caused by renal nerve stimulation. They further suggest the presence of presynaptic alpha 2‐adrenoceptors on those nerves innervating the renal tubules.
Oscillatory hyperpolarizations and resting membrane potentials of mouse fibroblast and macrophage cell lines.
Authors: Ince C , Leijh P C , Meijer J , Van Bavel E , Ypey D L
Published: December 2014

L cells (a mouse fibroblast cell line) and macrophages have been reported to exhibit slow oscillatory hyperpolarizations and relatively low membrane potentials, when measured with glass micro‐electrodes. This paper describes the role of micro‐electrode‐induced leakage in these oscillations for L cells and a mouse macrophage cell line (P388D1). Both L cells and macrophages showed fast negative‐going peak‐shaped potential transients upon micro‐electrode entry. This shows that the micro‐electrode introduces a leakage conductance across the membrane. The peak values of these fast transients were less negative for L cells (‐17 mV) than for macrophages (‐39 mV), although their sustained resting membrane potentials were about equal (‐13 mV). This indicates that the pre‐impaled membrane potential of macrophages is more negative than that of L cells. Ionophoretic injection of Ca2+ into the P388D1 macrophages showed the existence of a Ca2+ ‐dependent hyperpolarizing conductance presumed to be involved in the oscillatory hyperpolarizations of L cells and macrophages. Cells increased in size by X‐ray irradiation to reduce membrane input resistances were still found to be susceptible to micro‐electrode‐induced leakage. Impalement transients upon entry of a second electrode during a hyperpolarization evoked by a first electrode, were often step‐shaped instead of peak‐shaped due to the high membrane conductance associated with hyperpolarization. Since peak‐shaped impalement transients were always seen with the first impalement both in oscillating and non‐oscillating cells, oscillatory hyperpolarizations cannot be regarded as spontaneously occurring in the unperturbed cells but are induced by micro‐electrode penetration. Since the hyperpolarizing response can be evoked by ionophoretic injection of Ca2+, and oscillatory as well as single hyperpolarizing responses are absent in a Ca2+ ‐free medium, it is concluded that the Ca2+ needed intracellularly to activate the hyperpolarizing responses enters the cell via the leakage pathway introduced by the measuring electrode.
Intracellular calcium ions and calcium currents in perfused neurones of the snail, Lymnaea stagnalis.
Authors: Byerly L , Moody W J
Published: December 2014

Neuronal somata of Lymnaea stagnalis were internally perfused and voltage clamped using the suction pipette method. The cells were exposed to internal solutions buffered to various concentrations of Ca2+ while the cytoplasmic Ca2+ activity [( Ca2+]i) was monitored with a Ca2+ ‐sensitive micro‐electrode. [Ca2+]i was usually about 10(‐7) M when the cell was perfused with a solution buffered to any level of Ca2+ from 9 X 10(‐7) to below 10(‐8) M. With internal solutions buffered to 10(‐6) M‐Ca2+ or greater, [Ca2+]i increased rapidly and overshot the perfusate Ca2+ activity by up to two orders of magnitude. It was thus virtually impossible to hold [Ca2+]i steady at any levels other than about 10(‐7) M or 10(‐4) M using internal perfusion of simple ionic internal solutions. The excess Ca2+ which caused the overshoot of [Ca2+]i entered the cell from the external solution through Cd2+ ‐sensitive channels. Cd2+ in the external solution prevented or reversed the overshoot of [Ca2+]i and brought [Ca2+]i to near the perfusate level. ATP added to the internal solution also prevented [Ca2+]i from overshooting the perfusate level during perfusion with high‐Ca2+ buffers. By monitoring [Ca2+]i with a Ca2+ ‐sensitive micro‐electrode, we were able to estimate the relationship between [Ca2+]i and the Ca2+ current (ICa) measured under voltage clamp. ICa was completely blocked as [Ca2+]i was raised to 10(‐6) M. We believe that the discrepancy between our data and other estimates of the ICa vs. [Ca2+]i relationship using internal perfusion of molluscan nerve cells results from the incorrect assumption that [Ca2+]i is controlled adequately during internal perfusion.
The effect of local anaesthetics on the components of the asymmetry current in the squid giant axon.
Authors: Bekkers J M , Greeff N G , Keynes R D , Neumcke B
Published: December 2014

The effects of local anaesthetics and holding potential on sodium and asymmetry currents were studied in intracellularly dialysed squid giant axons. The asymmetry currents were fractionated into their inactivating and non‐inactivating components, and the charge displacements Qi and Qn of the two components were determined for pulse potentials between ‐20 and +40 mV. The charged local anaesthetic RAD 366, a quaternary derivative of lidocaine, applied internally at a concentration in the dialysis solution of 1 mM, did not change Qn, but reduced Qi about 3‐fold. The neutral local anaesthetic benzocaine, applied externally at a concentration in the bathing solution of 1 mM, had effects very similar to RAD 366. It did not change Qn, but reduced Qi and the sodium current about 2 . 5‐fold. Unlike local anaesthetics, steady membrane depolarization had essentially equal effects on Qn, Qi and sodium current. Lowering the holding potential from ‐98 to ‐60 mV for several minutes reduced all three variables to about half. Models of sodium channel voltage‐gating are discussed which implicate both Qn and Qi, and which account for the selective blockage of Qi by sodium inactivation and local anaesthetics.
Resonance at the wrist demonstrated by the use of a torque motor: an instrumental analysis of muscle tone in man.
Authors: Lakie M , Walsh E G , Wright G W
Published: December 2014

The resonance of the relaxed wrist for flexion‐extension movements in the horizontal plane has been investigated by using rhythmic torques generated by a printed motor. In the normal subject the resonant frequency of the wrist is ca. 2 Hz unless the torque is reduced below a certain critical value when the system is no longer linear and the resonant frequency rises. This critical torque level, and the damping are both less in women than men. The resonant frequency is uninfluenced by surgical anaesthesia. With added bias the increase of resonant frequency at low torques still occurs although the hand is now oscillating about a displaced mean position. It follows that the stiffening implied by this elevation of resonant frequency for small movements is neither the result of pre‐stressing of the muscles nor of reflex activity. With velocity feed‐back of appropriate polarity the system will oscillate spontaneously at its resonant frequency. If the peak driving torque is progressively reduced the resonant frequency increases abruptly, indicating that the system has stiffened. Perturbations delivered to the wrist may reduce its stiffness. The postural system is thixotropic with a 'memory time' of 1‐2 s. The resonant frequency is elevated in voluntary stiffening.
Ultradian rhythm of growth hormone secretion and sleep in the adult male rat.
Authors: Kimura F , Tsai C W
Published: December 2014

The correlation between growth hormone (GH) secretion and the sleep‐wakefulness cycle in the adult male rat was studied by serial blood sampling at 10 min intervals. Electroencephalograms (e.e.g.s) recorded continuously during the blood sampling were scored into wakefulness and sleep, and the amount of sleep for every 10 min was plotted against the GH value as assessed by radioimmunoassay. The power spectrum analysis and the least‐squares method applied to the time series of GH concentrations in the control rat revealed that the mean (+/‐ S.E. of the mean) periodicity was 2.93 +/‐ 0.10 h for the period from 00.00 to 12.00 h in five rats and 2.85 +/‐ 0.06 h for the period from 12.00 to 24.00 h in eight rats. For the animals in which the e.e.g. was recorded simultaneously with blood samplings from 12.00 to 24.00 h, the cross‐correlation analysis performed between the time series of the amount of sleep and the GH value revealed a significant positive correlation at time lags of 0‐10 min in six and at time lags of 20‐50 min in four out of fourteen rats. The number of animals having a positive correlation at short time lags seemed relatively less, but in most animals, there was observed a definite relationship that each GH peak occurred with a consistent time lag ranging from 40 to 70 min following the onset of sleep cycle. Sleep deprivation performed from 13.00 to 16.00 h during the sampling period from 11.00 to 19.00 h was effective in preventing high‐level GH pulses which otherwise should appear during this time of the day. Concurrent measurements of corticosterone concentrations in the sleep‐deprivation experiment revealed that peak values of corticosterone secretory episodes were not influenced by sleep deprivation. These findings indicate that the GH secretion in the adult rat is also correlated with the sleep‐wakefulness cycle, although somewhat differently from the immature rat.
Control of mucoglycoprotein output from the rabbit nose.
Authors: Pell J , Phipps R J , Wells U M , Widdicombe J G
Published: December 2014

A method for the collection of rabbit nasal washings to analyse outputs of mucous glycoproteins is described. The radiolabels sodium [35S]sulphate and [3H]glucose are bound to the glycoproteins. The release of bound 35S and 3H was enhanced by cervical sympathetic nerve stimulation. Adrenoceptor agonists (phenylephrine, dobutamine and salbutamol) given I.V. increased the output of 35S, and the last two drugs increased the output of 3H. The blocking effects of thymoxamine and propranolol on these responses are described. Pilocarpine (given I.V. or intranasally) produced large increases in 35S release; histamine had little effect. Irritants (ammonia and cigarette smoke) and diluted serum or plasma, given intranasally, produced large increases in 3H output, and sometimes enhanced 35S release. Radiolabelled nasal washings fractionated on Sepharose CL‐4B gel chromatography columns formed two peaks, with most of the radioactivity in the high molecular weight (mucous glycoprotein) peak.
An excitatory pathway through dorsal columns to rubrospinal cells in the cat.
Authors: Jeneskog T , Padel Y
Published: December 2014

A somaesthetic excitatory pathway to rubrospinal cells, via other than cortico‐ or cerebello‐rubral relays, has been demonstrated in cats, using intracellular recording techniques. After lesions of the rostral part of the cerebral cortex and the cerebellum, electrical stimulation of the contralateral forepaw and low intensity stimulation of the dorsal columns produced excitatory post‐synaptic potentials (e.p.s.p.s) in rubrospinal cells, which often reached the threshold for firing bursts of spikes. These somaesthetic e.p.s.p.s are composed of a burst of small elementary e.p.s.p.s which progressively create a depolarization with a long‐lasting time course. Evidence has been obtained that the pathway runs through the dorsal columns to reach the red nucleus after a relay. Stimulation applied to the dorsal columns gives rise to the response with very low threshold current, close to 20 microA. Also, the firing pattern of lemniscal fibres to single‐shock dorsal column stimulation has been correlated with the time course of excitation of the rubrospinal cells. As calculated from latencies of e.p.s.p.s the conduction velocity in the investigated pathway is over 55 m/s in the peripheral nerve fibres, indicating that thick, myelinated fibres are involved. It is suggested that the fast somaesthetic loop might, via the rubrospinal tract, participate in exploratory motor behaviour and in the adaptation of gait to the environment.
Differential effects of ischaemia and hyperkalaemia on myocardial repolarization and conduction times in the dog.
Authors: Donaldson R M , Nashat F S , Noble D , Taggart P
Published: December 2014

The role of increased extracellular K+ concentration ([K+]o) in the production of the early electrophysiological changes induced by myocardial ischaemia, was evaluated by recordings of monophasic action potentials and the paced endocardial evoked response. Changes in the duration of local repolarization and conduction time were evaluated during ischaemia, K+ infusion and hypoxia. Raising [K+]o levels in systemic arterial blood from 3.4 +/‐ 0.5 mmol l‐1 to 5.9 +/‐ 1.5 mmol l‐1 produced a similar shortening of repolarization as was seen during ischaemia. Prolongation of conduction time occurred only when the [K+]o levels rose to 8.8 +/‐ 1.3 mmol l‐1. The conduction time slowing during acute ischaemia was always greater and occurred at lower [K+]o levels than that produced by K+ infusion at rates equivalent to the post‐ischaemic myocardial venous effluent. Monophasic action potential amplitude and upstroke velocity were reduced in ischaemia but not markedly affected by the increase in [K+]o. Absolute reduction in repolarization time during K+ infusion was more marked at the apex than at the base in the epicardial recordings. The superimposition of hypoxia on hyperkalaemia resulted in marked slowing of repolarization and conduction time. Many but not all of the early electrophysiological abnormalities of acute ischaemia in the intact heart can be related to raised [K+]o.
Trifluoperazine reduces inward ionic currents and secretion by separate mechanisms in bovine chromaffin cells.
Authors: Clapham D E , Neher E
Published: December 2014

Using patch‐clamp techniques, excitation and secretion in chromaffin cells were studied by measurement of unitary inward currents and of stimulus‐evoked increments in membrane capacitance. The effect of the calmodulin inhibitor trifluoperazine (TFP) on Na, Ca and acetylcholine‐induced (ACh) currents as well as on capacitance increments was investigated. TFP in concentrations up to 10 microM had no effect on Na channel currents. TFP was a potent anticholinergic agent. TFP in concentrations of 100 nM‐1 microM decreased net ACh‐induced currents by a slow block or allosteric modification of the channel. The effect was only partially reversible. Recovery from desensitization was retarded in direct relation to [TFP]. At the single channel level, TFP was found to slightly shorten open times in 0.5 and 20 microM‐ACh. As reported previously, desensitization can be modelled by at least two desensitized states, as reflected by the bursting and clustering behaviour of single channels. TFP shortened clusters mainly by reducing the number of bursts per cluster. Whole‐cell Ca currents (ICa) were reduced in 10 microM‐TFP from an average of 29 microA cm‐2‐13 microA cm‐2. Changes in capacitance of 1‐200 fF were elicited in controls by maximal activation of the Ca current. We interpreted these steps to be the summed result of many exocytotic vesicular fusion events. Capacitance steps depended on ICa and were absent when extracellular Ca was removed. Application of 10 microM‐TFP inhibited capacitance steps. The block of capacitance steps by TFP was shown to be independent of the reduction of ACh and Ca inward ionic currents. We conclude that the prevention of exocytosis by TFP is not completely described by its inhibition of electrical excitability but also results from intracellular actions.
Non‐selective conductance in calcium channels of frog muscle: calcium selectivity in a single‐file pore.
Authors: Almers W , McCleskey E W
Published: December 2014

Voltage‐clamp studies were carried out to compare currents through Ca2+ channels (ICa) with Na+ currents (Ins) through a non‐selective cation conductance blocked by micromolar concentrations of external Ca2+. The gating of both currents was found to have similar time and voltage dependence. The amplitudes of ICa and Ins varied widely, but Ins was always large in fibres with large ICa, and small in fibres with small ICa. Both ICa and Ins were blocked by the specific Ca2+ channel blocker nifedipine, with half‐blockage concentrations that were virtually identical (KD = 0.9 microM for ICa and 0.7 microM for Ins). ICa and Ins were also equally sensitive to block by diltiazem (KD = 80 microM). These parallels between Ins and ICa are most easily explained if Ins flows through Ca2+ channels. Apparently, Ca2+ channels bear high‐affinity Ca2+‐binding sites, and are highly permeable to monovalent cations when Ca2+ is absent. Ba2+ currents (IBa) and ICa were measured in external solutions containing mixtures of Ba2+ and Ca2+. IBa is blocked by Ca2+, as is Ins. Adding Ba2+ to Ca2+ produces only small or no increases in current, as if Ba2+ is only sparingly permeant when Ca2+ is present. Membrane currents in Ba2+/Ca2+ mixtures show anomalous mole‐fraction behaviour, suggesting that Ca2+ channels are single‐file, multi‐ion pores. Complex current transients are observed under maintained depolarizations in Na+/Ca2+ and Ba2+/Ca2+ mixtures. They suggest that in ion mixtures, Ca2+ channels transport Ca2+ in preference to Na+ and Ba2+. Hence Ca2+ channels are selective for Ca2+, even though current amplitudes suggest that the Na+ or Ba2+ permeabilities in the absence of Ca2+ are as high as, or higher than, the Ca2+ permeability. We conclude that the selective permeability of Ca2+ channels depends on the presence of Ca2+. In model calculations, our observations are explained as a consequence of Ca2+ channels being single‐file pores. It is proposed that Ca2+ channels derive much of their ion selectivity from high‐affinity Ca2+ binding sites located in an otherwise unselective aqueous pore.