bluuebunny/crossref_metadata_2025 huggingface dataset:
The occlusion of sodium ions within the mammalian sodium‐potassium pump: its role in sodium transport.
Authors: Glynn I M , Hara Y , Richards D E
Published: December 2014

The hypothesis that the ADP‐sensitive form of phosphorylated Na+, K+‐ATPase contains occluded sodium ions has been tested by a procedure which involves (i) modifying the enzyme with alpha‐chymotrypsin or N‐ethylmaleimide (NEM) so that the ADP‐sensitive form is more stable than it is in the native enzyme, (ii) phosphorylating the modified enzyme with ATP in the presence of labelled sodium ions, and (iii) forcing the phosphorylated enzyme rapidly through a cation‐exchange column and measuring the labelled sodium in the effluent. The results show that ADP‐sensitive phosphoenzyme prepared from alpha‐chymotrypsin‐ or NEM‐modified Na+, K+‐ATPase is able to carry labelled sodium ions through a cation‐exchange resin. This behaviour was not seen with native Na+, K+‐ATPase or when phosphorylation was prevented by the omission of magnesium ions or by the substitution of adenylyl(beta, gamma‐methylene)diphosphonate (AMP‐PCP) for ATP. The occluded sodium ions were rapidly released when the phosphoenzyme was dephosphorylated by ADP. When alpha‐chymotrypsin‐modified enzyme was phosphorylated by ATP with 1 mM‐sodium in the medium, close to three sodium ions were occluded per phospho group. The stoicheiometry at much lower sodium concentrations could not be determined satisfactorily. A consideration of the rate constants of the reactions thought to be involved in the occlusion of sodium and in the release of sodium from the occluded state shows that, so far as they are known, these constants are compatible with the hypothesis that the occluded‐sodium form of the phosphoenzyme plays a central role in sodium transport through the pump.
Potassium current in clonal cytotoxic T lymphocytes from the mouse.
Authors: Fukushima Y , Hagiwara S , Henkart M
Published: December 2014

The electrical properties of the cell membrane of clonal cytotoxic T lymphocytes in the mouse were studied by using the whole cell variation of the patch electrode voltage‐clamp technique. Outward currents were activated with an exponential time course of several milliseconds time constant when the membrane potential was made more positive than ‐50 to ‐40 mV. This current is not activated as a result of Ca2+ entry. The estimated reversal potential of the current indicates that the current is predominantly carried by K+. The activation kinetics depend only on membrane potential, not on [K+]0. The amplitude of the current decreases exponentially with time constants of several hundred milliseconds during a maintained voltage pulse, due mainly to a decrease in conductance. Recovery from inactivation roughly followed a single exponential time course with a time constant of tens of seconds; this time constant depended upon not only the membrane potential but also the amount of initial inactivation. The current is suppressed by quinidine and tetraethylammonium, their half‐suppression concentrations being 23 microM and 14 mM respectively. An increase of the outward current is suggested to be associated with the lethal hit of the cytotoxic reaction.
Factors affecting proximal tubular acidification of non‐bicarbonate buffer in the rat.
Authors: Amorena C , Fernandes D T , Malnic G
Published: December 2014

The effect of peritubular PCO2 and pH changes within the physiological range on proximal tubular acidification of non‐bicarbonate (phosphate) buffer was evaluated with and without carbonic anhydrase inhibition by stopped‐flow microperfusion and Sb micro‐electrode techniques. Luminal steady‐state pH was reduced from 6.69 to 6.37 and H ion fluxes (JH+) increased from 0.63 to 1.57 nmol cm‐2 s‐1 by increasing capillary CO2 from 0 to 9.6% at pH 7.2. After acetazolamide a marked, although attenuated, effect of CO2 on acidification was still observed; JH+ increased from 0.088 nmol cm‐2 s‐1 at 0% CO2 to 0.78 at 9.6% CO2. Most of this effect can be explained by titration of luminal buffer by CO2, uncatalysed CO2 hydration and H2CO3 recirculation. An increase in capillary CO2 reduced acidification half‐times (t/2), which, according to an analogue circuit model, may be due to increased H ion access to the pump. Peritubular pH changes at 0% CO2 also modified tubular acidification, increasing JH+ from 0.73 nmol cm‐2 s‐1 at pH 7.6 to 0.99 at pH 7.0. After acetazolamide, JH+ still increased from 0.11 nmol cm‐2 s‐1 at pH 7.6 to 0.57 at pH 7.0. In conclusion, both peritubular CO2 changes at constant pH and pH changes at 0% CO2 were effective to modify JH+, in the presence and absence of carbonic anhydrase activity. In the studied range, capillary CO2 induced larger changes in JH+ than pH. The data show substrate (H ion) is a limiting factor for tubular H ion secretion.
Effect of cooling on supraoptic neurohypophysial neuronal activity and on urine flow in the rat.
Authors: Ferguson A V , Pittman Q J , Riphagen C L
Published: December 2014

The activity of antidromically identified supraoptic neurosecretory neurones was recorded in Sprague‐Dawley rats under urethane or sodium pentobarbitone anaesthesia during cooling of the body with a cold pack. Of twelve phasic neurones studied during a complete cooling and rewarming cycle, six displayed an initial increase, followed by a depression in activity during the period of reduced body temperature. The remaining six phasic neurones did not alter their activity during cooling. Non‐phasic neurohypophysial neurones displayed a reversible reduction (n = 8), or increase (n = 6) in activity during cooling, while seven neurones were unaffected by changes in body temperature. In four other anaesthetized Sprague‐Dawley rats, urine flow was reduced by approximately 50% during cooling; this was followed by a diuresis after removal of the cold pack and return of body temperature to normal. The antidiuresis did not occur in homozygous Brattleboro rats which lack arginine vasopressin. The electrophysiological data from a proportion of the supraoptic neurohypophysial neurones correlate with the observed changes in urine flow.
Nerve growth and ectopic synapse formation induced by muscle damage in the frog.
Authors: Sayers H , Tonge D A
Published: December 2014

The effect of muscle damage on nerve growth and ectopic synapse formation in the frog was investigated by bisecting the cutaneus pectoris (c.p.) muscle following implantation of the hypoglossal nerve. Axons from the stump of the implanted nerve grew considerable distances towards the ends of the cut muscle fibres where they formed synapses. In some preparations, c.p. was only partially cut and in these muscles axonal growth from the implanted nerve occurred across intact fibres to reach the cut ends in the damaged area, suggesting the local release of a growth‐stimulating factor. Stimulation of the hypoglossal nerve elicited contraction of the end‐plate‐free half of c.p. The characteristics of these ectopic synapses were similar to those found in a previous study when the hypoglossal nerve innervated the original end‐plates after denervation of c.p. The mean quantal content of the end‐plate potentials (e.p.p.s) was abnormally low, with long latencies between nerve stimulation and the onset of the e.p.p.s and frequent occurrence of multiphasic e.p.p.s in response to single nerve stimulation.
Distribution of receptors for acetylcholine and 5‐hydroxytryptamine on identified leech neurones growing in culture.
Authors: Pellegrino M , Simonneau M
Published: December 2014

The spatial distribution of receptors on identified leech neurones removed from the C.N.S. and grown in culture has been studied by applying acetylcholine (ACh) and 5‐hydroxytryptamine (5‐HT) ionophoretically and by pressure. Two cells were selected: a neurone called anterior Pagoda (Ap), that shows responses to ACh, and the pressure sensory neurone (P cell), upon which 5‐HT synapses form in culture. ACh receptors of Ap neurones in culture had properties similar to those of their counterparts in situ. Thus, ACh responses of Ap cells were mediated by Cl‐ and were blocked by curare and alpha‐bungarotoxin. The cell bodies of these neurones in culture had low (10 mV/nC) and uniform sensitivity to ACh over the surface of the soma. When a sprout grew out from the Ap cell, a region of increased sensitivity appeared at its base, with a gradient of sensitivity decreasing toward the tip of the neurite. Characteristically, the base was 3‐5 times more sensitive to ACh than the soma or the growth cone. Cells with multipolar processes developed a similar pattern of sensitivity for each sprout. P sensory neurones in culture showed similar distributions of sensitivity to 5‐HT and ACh. Experiments made with voltage clamp suggested that the non‐uniform responses to transmitter represent true differences in sensitivity. Together these findings suggest that the receptors for ACh and 5‐HT have a greater density at the base of each neurite compared to that of the soma and the tip.
Tendon organ firing during active muscle lengthening in awake, normally behaving cats.
Authors: Appenteng K , Prochazka A
Published: December 2014

Recordings were obtained of the discharge of single tendon organ (Ib) and muscle spindle (Ia) afferents of the ankle extensor muscles during movement in normal cats. During very slow, smooth increases and decreases in muscle force, Ib afferents showed from one to five stepwise changes in firing rate, attributable to the recruitment of motor units inserting into the receptor capsule. These 'recruitment steps' in Ib firing rate became smoothed and tended to merge during faster variations in muscle force, and were rarely discernible in normal movements such as slow stepping. Rapid imposed stretches resulted in Ib firing patterns which fitted well a dynamic function of whole muscle force. Comparisons were made between the responses of Ib and Ia afferents during rapid, imposed muscle stretch. The segmentation of discharge typical of Ia afferents was not present in Ib afferents, despite segmentation of the e.m.g. of the receptor‐bearing muscles. This would imply that Ib afferents exert a rapidly fluctuating reflex action against a relatively steady background of Ib input. Ankle extensor Ib firing during stepping was characterized by feeble firing during the swing phase and substantial, smoothly modulated firing during the stance phase. Taken together with previous chronic recordings, the data support the view that the ensemble of Ib afferents from a muscle signals a dynamic, non‐linear function of whole muscle force over a wide range of normal movement.
Autonomic regulation of mucociliary transport rate in the oesophagus of the frog, Rana temporaria.
Authors: Morley J , Sanjar S
Published: December 2014

Transport of lead particles along the mucosal surface of the frog oesophagus has been measured by direct observation with the aid of video recording. Electrical stimulation of the vagus nerve increased the rate of particle transport. This acceleration was suppressed by atropine or by hexamethonium. Acetylcholine and other parasympathomimetic agents accelerated particle transport rate. Such acceleration was abolished by atropine. Nicotine increased the rate of particle transport and this effect was suppressed by hexamethonium or by atropine. Atropine did not significantly alter basal particle transport rate. Neither basal particle transport rate nor the response to vagal nerve stimulation were affected by eserine. Adrenaline, noradrenaline or isoprenaline did not affect basal particle transport rate. Adrenaline or noradrenaline were without effect on the increased particle transport rate due to electrical stimulation of the vagus.
Non‐stationary fluctuations of the potassium conductance at the node of ranvier of the frog.
Authors: Conti F , Hille B , Nonner W
Published: December 2014

Potassium currents were recorded from voltage‐clamped nodes of isolated, myelinated axons of Rana pipiens. Nodes were maintained in a modified Ringer solution containing tetrodotoxin to block sodium current and 47.5 mM‐potassium to minimize effects of extracellular potassium accumulation. Voltage protocols included depolarizing pulses lasting a few milliseconds to several seconds. Fluctuations about the ensemble average of the current were characterized in terms of non‐stationary variance and autocovariance. The fluctuations had a Gaussian amplitude distribution and were virtually free of contaminations from systematic variations of the membrane current. Corrections for background noise were based on measurements done while potassium current was blocked with tetraethylammonium, and on simulations of extrinsic current fluctuations expected to arise from noise in the actual membrane voltage. The fluctuations were attributed to variations of nodal potassium conductance, since they were absent at the reversal potential of the potassium current and at membrane voltages that do not activate potassium current. Covariances indicated that voltage steps that reversed a macroscopic potassium current also reversed the sign of the fluctuation. Plots of the conductance variance versus the mean potassium conductance were generated from both the activation and deactivation (tail) phases of the potassium currents at various voltages between ‐80 and +70 mV. When the current was activated by a small depolarization (‐50 mV) the trajectories from both phases were indistinguishable and were fitted by the parabola expected for a single population of channels with only one open‐channel conductance. Apparent single‐channel conductance from the early activation phase averaged 24 pS and was not significantly voltage dependent. In contrast, experiments with large depolarizations (+10 to +70 mV) gave significantly different variance‐‐mean trajectories during activation and deactivation and these trajectories were poorly fitted by parabola. This result indicates that the fluctuations reflect several populations of channels and/or a population of channels that can have several levels of non‐zero conductance. Projections of the fluctuation covariance showed long correlations, as well as the rapidly decaying component expected from the activation gating of channels. A slow fluctuation arose at a time slightly later than the rise of potassium current, spanned the entire length of brief depolarizations, and extended up to 880 ms during long depolarizations.(ABSTRACT TRUNCATED AT 400 WORDS)
The actions of gamma‐aminobutyric acid, glycine and their antagonists upon horizontal cells of the Xenopus retina.
Authors: Stone S , Witkovsky P
Published: December 2014

We examined the effects of gamma‐aminobutyric acid (GABA) and glycine and their respective antagonists, picrotoxin and strychnine, upon the membrane potential and light‐evoked responses of the type H1 horizontal cell of the Xenopus retina. This horizontal cell receives mixed input from rod and cone receptors. Under control conditions the mean membrane potential was ‐37.8 +/‐ 9.7 mV. Addition of 5 mM‐GABA to the superfusate hyperpolarized the cell by 4.0 +/‐ 2.6 mV within 3‐5 min; addition of 0.5 mM‐picrotoxin depolarized the cell by 4.3 +/‐ 2.1 mV. Prolonged (greater than 15 min) exposures to the drugs elicited more pronounced changes in membrane potential. GABA and picrotoxin affected primarily the cone‐dependent input to the H1 horizontal cell. Under dark‐adapted conditions, response wave forms were essentially unaltered by the drugs, but when the horizontal cell was moderately or fully light adapted, GABA reduced and picrotoxin enhanced the cone‐dependent component of its response to light. Long‐term (greater than 15 min) exposures to GABA and picrotoxin elicited changes in response kinetics usually associated with dark and light adaptation, respectively. Glycine, at bath concentrations of 0.6 mM or greater, depolarized horizontal cells by 21 mV on average and reduced or abolished their light response. This action did not occur in the presence of 0.1 mM‐strychnine. When all light‐evoked activity was blocked by 20‐40 mM‐magnesium, the depolarizing action of glycine still occurred. Thus, glycine appears to act directly upon the horizontal cell membrane. Neither GABA nor glycine, nor their respective antagonists, affected the spatial extent of the horizontal cell receptive field.
Lack of selectivity to small ions in paracellular pathways in cerebral and muscle capillaries of the frog.
Authors: Crone C
Published: December 2014

Selectivity to passive permeation of small ions through capillary walls was studied by measurements of diffusion potentials in response to ionic gradients established across capillary walls in frog brain and muscle in superfusion and perfusion experiments. Average dilution potentials in response to 2:1 or 10:1 gradients of NaCl across brain capillaries were 4.2 and 10.2 mV, respectively. The 'diluted' side was negative with respect to the 'undiluted' side, reflecting higher mobility of Cl‐ than of Na+ ions. Bi‐ionic potentials in response to isosmotic KCl:NaCl gradients averaged 5.0 mV in brain capillaries, negative on the KCl side, reflecting higher mobility of K+ than of Na+ ions. The potential variations were symmetrical across the capillary wall. From Planck‐Henderson formalism, the relative permeabilities in brain capillaries of Na+, K+ and Cl‐ were PCl/PNa:1.54 and PK/PNa:1.56, rather close to mobility ratios in free solution. Experiments on muscle capillaries showed similar results to those in brain. Streaming potentials created with excess (200 mosmol) mannitol or sucrose were congruent to 1 mV in brain capillaries and zero in muscle capillaries. It is concluded that the transcapillary permeation pathway in muscle and brain is neutral or weakly charged. The dominant ion permeation is paracellular in all 'continuous' capillaries. The large range of ion permeability of 'continuous' capillaries may be explained by variation in the length of the effective open portion of interendothelial junctions. The very low passive permeability of the blood‐brain barrier may be due to an almost closed endothelial junction, leaving only about 0.1% of the length open. The open fraction is functionally similar to that in muscle and mesentery. This interpretation is in accordance with a finite, but very low, permeability to hydrophilic non‐electrolytes. Such a brain capillary would still display strong preference for lipid‐soluble solutes, but its behaviour cannot be satisfactorily understood from a simple analogy to a cellular plasma membrane.
Absorption of the cerebrospinal fluid and intracranial compliance in an amphibian, Rana pipiens.
Authors: Jones H C , Taylor C M
Published: December 2014

Experiments have been carried out to investigate the absorption of the cerebrospinal fluid (c.s.f.) and the intracranial compliance in an amphibian, Rana pipiens, using infusions into the c.s.f. system through glass micropipettes. Resistance to absorption of the c.s.f. was estimated by the constant rate infusion technique. Mean absorption resistance for infusions of artificial c.s.f. into the lateral ventricles and into the cerebral subarachnoid space were 15.48 and 16.52 mmH2O min microliter‐1 respectively. This difference was not significant and it is concluded that the pores in the posterior tela situated in the roof of the fourth ventricle do not offer any resistance to the flow of c.s.f. out of the ventricles. The resistance to drainage of the c.s.f. in this amphibian is higher than that found for mammals. Mean resting c.s.f. pressure, estimated from the intercept of the regression line with the pressure axis at zero infusion rate was 18.0 mmH2O. Absorption resistance was measured from the cerebral subarachnoid space before and after injection of 4 microliter Indian ink solution. There was a 3‐fold increase in resistance following ink injection. Two‐way analysis of variance showed the difference to be significant (P less than 0.01) suggesting that the outflow sites can become partially blocked by particulate matter. During a continuous 3 h infusion of artificial c.s.f. containing [14C]dextran or [125I]‐labelled human serum albumin (RISA) into the lateral ventricles, the mean percentage uptakes into the systemic circulation after the first 0.5 h of a 3 h period were 74.1 and 61.9% respectively. The difference is not significant. The rapid and high uptake into blood suggests there is a direct communication between c.s.f. and blood in amphibians. During continuous infusion of RISA into the lateral ventricles, simultaneous blood samples were taken from the femoral artery and the internal dorsal vertebral vein. Radioactivity was found to be 13.2% higher in venous samples. This suggests that at least some c.s.f. drainage takes place directly into the spinal venous system. Intracranial compliance was investigated by recording the peak pressure in response to a series of bolus injections of artificial c.s.f. into one lateral ventricle. Compliance was estimated to be 0.11, 0.10 and 0.09 microliter mmH2O‐1 for injection rates of 12.74, 16.62 and 25.10 microliters min‐1 respectively. The difference between these values is not significant. The results suggest that for injection volumes over 5 microliters the c.s.f. system behaves elastically.
Form, function and intracortical projections of spiny neurones in the striate visual cortex of the cat.
Authors: Martin K A , Whitteridge D
Published: December 2014

We have studied the neuronal circuitry and structure‐function relationships of single neurones in the striate visual cortex of the cat using a combination of electrophysiological and anatomical techniques. Glass micropipettes filled with horseradish peroxidase were used to record extracellularly from single neurones. After studying the receptive field properties, the afferent inputs of the neurones were studied by determining their latency of response to electrical stimulation at different positions along the optic pathway. Some cells were thus classified as receiving a mono‐ or polysynaptic input from afferents of the lateral geniculate nucleus (l.g.n.), via X‐ or Y‐like retinal ganglion cells. Two striking correlations were found between dendritic morphology and receptive field type. All spiny stellate cells, and all star pyramidal cells in layer 4A, had receptive fields with spatially separate on and off subfields (S‐type receptive fields). All the identified afferent input to these, the major cell types in layer 4, was monosynaptic from X‐ or Y‐like afferents. Neurones receiving monosynaptic X‐ or Y‐like input were not strictly segregated in layer 4 and the lower portion of layer 3. Nevertheless the X‐ and Y‐like l.g.n. fibres did not converge on any of the single neurones so far studied. Monosynaptic input from the l.g.n. afferents was not restricted to cells lying within layers 4 and 6, the main termination zones of the l.g.n. afferents, but was also received by cells lying in layers 3 and 5. The projection pattern of cells receiving monosynaptic input differed widely, depending on the laminar location of the cell soma. This suggests the presence of a number of divergent paths within the striate cortex. Cells receiving indirect input from the l.g.n. afferents were located mainly within layers 2, 3 and 5. Most pyramidal cells in layer 3 had axons projecting out of the striate cortex, while many axons of the layer 5 pyramids did not. The layer 5 cells showed the most morphological variation of any layer, were the most difficult to activate by electrical stimulation, and contained some cells which responded with the longest latencies of any cells in the striate cortex. This suggests that they were several synapses distant from the l.g.n. input. The majority of cells in layers 2, 3, 4 and 6 had the same basic S‐type receptive field structure. Only layer 5 contained a majority of cells with spatially overlapping on and off subfields (C‐ and B‐type receptive fields).(ABSTRACT TRUNCATED AT 400 WORDS)
Effect of aldosterone on urinary kallikrein and prostaglandin excretion in the rat.
Authors: Fejes-Tóth G , Náray-Fejes-Tóth A
Published: December 2014

In an attempt to study the interrelationship between aldosterone, Na balance, prostaglandin (PG) and kallikrein excretion, we investigated the influence of adrenalectomy and aldosterone administration on kallikrein and PG excretion during dietary manipulation of extracellular volume in Sprague‐Dawley rats. Adrenalectomy decreased while aldosterone administration increased urinary kallikrein and PG excretion during both low and high Na intake. Aldosterone induced a prompt change in Na/K ratio; however, kallikrein and PG excretion increased gradually during the 7 days of treatment. When the animals were forced into a negative Na balance during the administration of aldosterone by reducing their Na intake, kallikrein and PG excretion still increased but to a lesser extent than on a constant diet. In adrenalectomized rats given only vehicle, shifting the diet to a low Na intake caused a decrease in kallikrein and PG excretion. Corticosterone failed to correct the changes evoked by adrenalectomy, and it did not reproduce the effects of aldosterone. It is concluded that the effect of aldosterone on kallikrein and PG excretion is not mediated by changes in extracellular volume; however, in the absence of aldosterone a change in Na balance itself may influence kallikrein and PG excretion.
High selectivity of calcium channels in single dialysed heart cells of the guinea‐pig.
Authors: Lee K S , Tsien R W
Published: December 2014

Membrane currents and action potentials were recorded in single ventricular cells obtained from guinea‐pig hearts by enzymatic dissociation. Ca2+ channel currents carried by Ba2+ or Ca2+ were recorded with a suction pipette (5‐10 microns diameter) for voltage clamp and internal dialysis. Currents through Na+, K+ and non‐selective monovalent cation channels were suppressed by suitable holding potentials and external and internal solutions. The dialysis method allowed exchange within minutes of alkali metal cations (e.g. Cs+) and small molecules (e.g. quaternary derivatives of lidocaine and verapamil). Nevertheless, Ca2+ channels remained functional for considerable periods, typically 20 min and sometimes more than 1 h. With Ba2+ outside and Cs+ inside, current flow through Ca2+ channels changed from inward to outward at strongly positive levels beyond a clear‐cut reversal potential Erev. Several methods for defining Erev were in close agreement: (1) zero‐crossing of leak‐subtracted peak current, (2) inversion of time‐dependent current changes during channel activation or inactivation, (3) inversion of drug‐sensitive current as defined by channel blockers such as Cd2+ or D‐600. Erev varied with external Ba2+ or internal Cs+. Erev increased by 29 mV per 10‐fold increase in Ba2+. Interpreted with constant‐field theory, Erev values correspond to PBa/PCs of approximately 1360. With 5 mM‐Ca2+ outside and 151 mM‐Cs+ inside, Ca2+ channel current reversed near + 75 mV, corresponding to PCa/PCs approximately 6000. Earlier measurements of Erev (Lee & Tsien, 1982) suggest that PCa/PK greater than 1000. At strongly positive membrane potentials where channel activation is maximal, the Ca2+ channel current‐voltage relationship is strongly non‐linear, with conductance increasing on either side of an inflexion point near Erev. Activation of inward or outward currents through Ca2+ channels follows a sigmoid time course, as expected if activation were a multi‐step process.
Intracellular free magnesium in neurones of Helix aspersa measured with ion‐selective micro‐electrodes.
Authors: Alvarez-Leefmans F J , Gamiño S M , Rink T J
Published: December 2014

Cytoplasmic free Mg2+ concentration, [Mg2+]i, was measured in identified neuronal cell bodies of the suboesophageal ganglia of Helix aspersa, using Mg2+‐selective micro‐electrodes. In calibration solutions, the electrodes showed significant interference from K+, but not from Na+, or Ca2+, at concentrations found intracellularly. Therefore, in order to calibrate the electrodes properly, it was necessary first to obtain an accurate value for intracellular free K+ concentration [( K+]i). The mean value for [K+]i was 91 mM (S.E. of the mean +/‐ 2.2 mM, n = 8), measured with K+‐sensitive 'liquid ion exchanger micro‐electrodes'. In seven experiments, which met stringent criteria for satisfactory impalement and electrode calibration, the mean [Mg2+]i was 0.66 mM (S.E. of the mean +/‐ 0.05 mM). The mean [Mg2+]i in cells that had spontaneous spike activity was not significantly different from that in quiescent cells. If Mg2+ was in electrochemical equilibrium, the ratio [Mg2+]i/[Mg2+]o would be about 55. Mg2+ is therefore not passively distributed across the neuronal membrane and an outwardly directed extrusion mechanism must exist to keep [Mg2+]i low and constant, even in cells undergoing spike activity.
A cholinergic link in the reflex release of vasopressin by hypotension in the rat.
Authors: Bisset G W , Chowdrey H S
Published: December 2014

Inhalation of amyl nitrite in the water‐loaded rat under ethanol anaesthesia produced a brief fall of blood pressure followed by a prolonged antidiuretic response. The antidiuretic response to amyl nitrite was accompanied by increased urinary excretion of vasopressin, it was blocked by a specific vasopressin antagonist and by a barbiturate and it was absent in the Brattleboro rat with congenital diabetes insipidus. These results show that the antidiuretic response to the hypotension induced by amyl nitrite is due to the release of vasopressin and that this release is mediated by a neuroendocrine reflex acting through the brain stem. Carbachol and nicotine produced an antidiuretic response on injection into a lateral cerebral ventricle (i. vent.). Carbachol was almost ineffective, but nicotine much more effective, when injected into the cisterna magna (i.cist.) from which in the rat there is no access to the ventricles. Carbachol therefore acts at a site reached from the ventricles, possibly the paraventricular nucleus. Nicotine acts at a more distal site reached from the subarachnoid space. This site may correspond with the nicotine‐sensitive area on the ventral surface of the brain stem which has been described in the cat. Atropine blocked the antidiuretic response to carbachol but not that to amyl nitrite. Hexamethonium blocked the antidiuretic response to amyl nitrite as well as that to nicotine and was more effective on i.cist. than i.vent. injection. These results reveal a cholinergic link with a nicotinic but not a muscarinic receptor in the neural pathways controlling the release of vasopressin in response to hypotension. A hypothetical model is presented in which the release of vasopressin is stimulated by a pathway arising from chemoreceptors and inhibited by a second pathway arising from stretch‐ and baroreceptors. Hypotension acts by suppressing the normally predominant inhibitory pathway and stimulating the excitatory pathway. Hexamethonium is presumed to block transmission at a synapse in the excitatory pathway at the ventral surface or, less probably, at the paraventricular and supraoptic nuclei.
The calcium current in inner segments of rods from the salamander (Ambystoma tigrinum) retina.
Authors: Corey D P , Dubinsky J M , Schwartz E A
Published: December 2014

Solitary rod inner segments were isolated from salamander retinae. Their Ca current was studied with the 'whole‐cell, gigaseal' technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981). The soluble constituents of the cytoplasm exchanged with the solution in the pipette. The external solution could be changed during continuous perfusion. Membrane voltage was controlled with a voltage clamp. After permeant ions other than Ca were replaced with impermeant ions (i.e. tetraethylammonium as a cation, and aspartate or methanesulphonate as an anion), an inward current remained. It activated at approximately ‐40 mV, reached a maximum at approximately 0 mV, and decreased as the membrane was further depolarized. The size of the current increased when Ba was substituted for external Ca. The current was blocked when Ca was replaced with Co. The voltage at which the current was half‐maximum shifted from approximately ‐22 to ‐31 mV during the initial 3 min of an experiment. The maximum amplitude of the current continuously declined during the entire course of an experiment. The time course for activation of the Ca current following a step of depolarization could be described by the sum of two exponentials. The time constant of the slower exponential was voltage dependent. Deactivation following repolarization could also be described by the sum of two exponentials. Both time constants for deactivation were independent of voltage (between ‐30 and 0 mV) and faster than the slower time constant for activation. When the internal Ca concentration was buffered by 10 mM‐EGTA, the Ca current did not inactivate during several seconds of maintained depolarization. When the concentration of EGTA was reduced to 0.1 mM, the Ca current declined and the membrane conductance decreased during several seconds of maintained depolarization. This inactivation was incomplete and only occurred after a substantial quantity of Ca entered. Following repolarization the Ca conductance recovered from inactivation. In contrast, the continuous decline observed during the course of an experiment (item 3) was not reversible. The difference suggests that inactivation and the decline are distinct processes.
Variation of calcium current during the cell growth cycle in mouse hybridoma lines secreting immunoglobulins.
Authors: Fukushima Y , Hagiwara S , Saxton R E
Published: December 2014

Ca currents of the cell membrane were recorded during a four‐day culture period using the whole‐cell variation of the patch electrode voltage clamp on a mouse myeloma cell line (S194, non‐secreting) and on two mouse hybridoma cell lines (MAb2‐1 which secretes immunoglobulin G (IgG) and MAb7B which secretes immunoglobulin M (IgM]. The density of Ca current increased during the four‐day culture period after cells were transferred into fresh medium. The average value of the maximum inward current per cell reached 57 +/‐ 15 pA (mean +/‐ S.D.) by the fourth day in hybridomas secreting immunoglobulins. The density of Ca current in hybridomas secreting IgG and IgM was greater than that in non‐secreting myeloma throughout the four days of the culture cycle. The cell density showed a sigmoidal increase during the culture period and the rate of increase in the density showed no significant correlation with the density of Ca current. The immunoglobulin level in the medium increased over the culture period, as did the estimated immunoglobulin secretion per cell per day. The time course of the increase of estimated individual cell secretion resembles that of the increase of density of Ca current.
Intracellular study of effects of histamine on electrical behaviour of myenteric neurones in guinea‐pig small intestine.
Authors: Nemeth P R , Ort C A , Wood J D
Published: December 2014

The actions of histamine on myenteric neurones were investigated with intracellular recording methods in guinea‐pig small intestine. The actions of histamine at the ganglion cell soma were: membrane depolarization, increased input resistance, suppression of post‐spike hyperpolarizing potentials, augmented excitability and repetitive spike discharge. Excitability was enhanced also at spike initiation sites remote from the cell body. Both H1, and H2, receptors were involved in the response to histamine. Dimaprit mimicked the responses to histamine in 80% and 2‐methylhistamine in 50% of the trials. Cimetidine was an antagonist for histamine in 82% and for dimaprit in all of the trials. Pyrilamine blocked the actions of histamine in 59% of the cells and always blocked the action of 2‐methylhistamine. Histamine mimicked slow synaptic excitation in the neurones, but was ruled out as a neurotransmitter for the slow excitatory post‐synaptic potential (e.p.s.p.). Histamine either did not affect the responses to 5‐hydroxytryptamine, substance P and acetylcholine or it potentiated the responses to these putative neurotransmitters for slow synaptic excitation. The results support the possibility that histamine released from mast cells by circulating peptidergic messengers, by neurotransmitters or during anaphylaxis could influence enteric nervous function.
Studies of the mechanism of noradrenaline stimulation of fluid absorption by rat jejunum in vitro.
Authors: Parsons B J , Poat J A , Roberts P A
Published: December 2014

The everted‐sac technique was used to study the mechanism of action of noradrenaline on fluid absorption by rat jejunum. Noradrenaline (10(‐3) M) significantly stimulated fluid absorption and this effect was dependent on the presence of calcium ions in the serosal fluid. Strontium, but not magnesium could substitute for calcium. Verapamil, manganese and neodymium, all inhibitors of calcium transport, blocked noradrenaline‐stimulated fluid absorption when present in the serosal compartment without any effect on basal or glucose‐stimulated absorption. Inhibitors of the translation stage of protein synthesis inhibited the response whereas blocking the transcription stage of protein synthesis was without effect. The noradrenaline response was not attenuated by tetrodotoxin suggesting that the response is not indirect due to noradrenaline altering endogenous intestinal nervous activity. It is concluded that noradrenaline acts by opening calcium channels in the basolateral membranes of epithelial cells, resulting in an influx of calcium which stimulates ribosomal protein synthesis to produce proteins involved in fluid transport.
The involvement of calcium in the intestinal response to secretagogues in the rat.
Authors: Hardcastle J , Hardcastle P T , Noble J M
Published: December 2014

The involvement of Ca2+ in the regulation of intestinal secretion was investigated in stripped sheets of rat mid‐intestine. Removal of serosal Ca2+ together with the addition of EGTA at concentrations of 0.5 and 1 mM inhibited the rise in short‐circuit current (s.c.c.) induced by both acetylcholine and theophylline, a similar degree of inhibition being observed with both secretagogues. Ca2+‐free serosal fluid with 0.5 mM‐EGTA added reduced significantly the rises in s.c.c. induced by A23187, acetylcholine, 5‐hydroxytryptamine, theophylline, dibutyryl cyclic AMP and prostaglandin E2, but not the increased s.c.c. associated with glucose absorption. The Ca2+ channel blocker verapamil produced similar results. The calmodulin antagonist trifluoperazine inhibited secretagogue action while its sulphoxide derivative was without effect at the same concentration. The intracellular Ca2+ antagonist TMB‐8 reduced the increased s.c.c. observed with acetylcholine and dibutyryl cyclic AMP. The net Cl‐ secretion, but not the decreased mucosal‐to‐serosal Na+ flux, induced by acetylcholine was abolished in Ca2+‐free conditions. There was no consistent effect on the reduction in the residual ion flux caused by acetylcholine. Absence of Ca2+ converted the stimulation of Cl‐ secretion induced by dibutyryl cyclic AMP observed under control conditions to an enhancement of net Na+ and Cl‐ absorption. It is concluded that intestinal secretagogues, whether they act through cyclic AMP or not, require both internal and external sources of Ca2+ if they are to produce their full effects. Moreover, it appears that the nature of the response to dibutyryl cyclic AMP depends on the prevailing Ca2+ concentration.
Effect of extracellular calcium on contractile activation in guinea‐pig ventricular muscle.
Authors: Kitazawa T
Published: December 2014

The problem of whether or not the alterations in twitch tension of mammalian cardiac muscle induced by changes in extracellular Ca concentration ([Ca]o) are due to the Na‐Ca exchange process across the surface membrane and/or the changes in the amount of Ca in the sarcoplasmic reticulum has been re‐examined by using thin bundles (70‐120 micron diameter) dissected from guinea‐pig papillary muscle. The observed time course of the change in the twitch tension due to a step change in [Ca]o was compared with that computed on a basis of the diffusion process of Ca ions in a circular cylinder and of the steady‐state relation between [Ca]o and twitch tension. After a sudden decrease in [Ca]o from 2 mM to various lower concentrations, the isometric twitch tension of the thin bundles first fell rapidly and monotonically and then showed a much smaller and slower secondary fall. The correspondence of the observed time course of the rapid phase with the predicted time course and the observed half‐time of the rapid phase ranging from 1.0 to 2.5 s indicate that the rapidity of the twitch response may be dominated by simple diffusion of Ca ions through the extracellular space. If so, the effective diffusion constant of Ca ions inside the bundles was 1.4 +/‐ 0.2 X 10(‐6) cm2/s (mean +/‐ S.E., n = 9). The magnitude and direction of the step change in [Ca]o or the change at different stimulus frequencies gave rise to dissimilar time courses of the contractile change; the difference in the rapid time courses due to these factors could be explained by the simple diffusion models, but not in the much slower phase. The half‐time for the Ca effect was the same as that for the rapid effect of Na ions in the external solutions. The time course of twitch decline due to [Ca]o decrease in the Na‐free (Li) solution was identical to that predicted from the time course measured in the Na‐rich solution and the steady‐state relation between [Ca]o and tension in the Na‐free solution. The half‐time of Ca leak from the sarcoplasmic reticulum in the skinned cardiac muscle was 40‐60 s in the presence of 10 mM‐EGTA, much shorter than that of the Ca leak in the skinned amphibian skeletal muscle, but much longer than that of twitch responses due to step changes in [Ca]o in the intact cardiac muscle.(ABSTRACT TRUNCATED AT 400 WORDS)
Plasticity of non‐giant flexion circuitry in chronically cut abdominal nerve cords of the crayfish, Procambarus clarkii.
Authors: Lee M T , Wine J J
Published: December 2014

We have investigated the pattern of neuronal activity involved in the gradual return of sensory‐evoked abdominal flexions in crayfish with chronically transected nerve cords. Recordings were made from eight types of identified neurone that mediate phasic abdominal movements, in a preparation consisting of the isolated abdominal nerve cord and tailfan. Responses of the cells to pinches and dorsiflexions of the tailfan were compared in two groups of animals: animals whose cords had been cut at the thoracic‐abdominal junction 4‐17 weeks earlier (chronic preparations), and animals whose cords had been cut at the same site either just before the experiment or up to 6 days earlier (acute preparations). Sensory stimuli produced bursts of spikes in 73% of the fast flexor motoneurones impaled in chronic preparations, but never fired these neurones in acute preparations. However, fast flexor motoneurones in both preparations were fired with approximately equal frequency by single impulses in the giant axons, suggesting that the firing thresholds of these motoneurones had not changed. Sensory stimuli also caused spiking in the extensor inhibitor and the flexor inhibitor in chronic preparations; in contrast, responses in the fast extensor motoneurones were always subthreshold and occasionally hyperpolarizing. None of these cells was fired by similar stimuli in acute preparations. Neurones restricted to the giant axon pathways (lateral, medial, segmental and motor giants) were silent during sensory‐evoked flexor discharges in chronically transected cords. Flexor discharges were accompanied by intense activity in non‐giant axons recorded from the dorsal cord. Two identified, non‐giant interneurones with axons in the dorsal cord were substantially depolarized but never fired by sensory input in chronic preparations. Sensory‐evoked firing in the fast flexor motoneurones was not abolished by removal of the posterior stump of the nerve cord at the transection site. About 20% of chronic preparations generated cyclic motor output in response to unpatterned sensory stimulation. The pattern of motor activity that develops in chronically transected cords resembles that seen in normal crayfish during non‐giant tailflips. Because cord transection permanently isolates the abdomen from rostral neural centres normally required for the generation of such tailflips, the return of co‐ordinated motor output in chronically cut cords may result from the sensory activation of non‐giant circuitry within the abdominal nervous system.
Electrical stimulation of the salivatory nucleus in the rat.
Authors: Donaldson J , Mitchell J , Templeton D
Published: December 2014

Unilateral electrical stimulation of the salivatory nucleus evoked a secretion from the ipsilateral parotid gland which was well maintained. Flow rate was not affected by sympathetic decentralization or by adrenoceptor antagonists but was abolished by atropine. Protein secretion was reduced by beta‐adrenoceptor antagonists but not by sympathetic decentralization or adrenalectomy. In support of previous histochemical findings it is concluded that the cells of the reticular formation are the origin of the preganglionic parasympathetic fibres to the salivary glands but that a beta‐adrenoceptor mechanism as yet unidentified is also involved in the protein secretion.
Effects of glucose removal and readmission on potassium contracture in the guinea‐pig taenia coli.
Authors: Ashoori F , Takai A , Tokuno H , Tomita T
Published: December 2014

The effects of removal and readmission of substrates on the K contracture were investigated in the guinea‐pig taenia coli. When, after exposure to excess K in Ca‐free and glucose‐free medium, the readmission and removal of 2.4 mM‐Ca were repeated at regular intervals, the Ca‐induced contractions decreased progressively. The decrease was more marked in the late than in the early part of the tension response. The rate of O2 consumption decreased when the normal medium was replaced by glucose‐free, Ca‐free, excess‐K solution, but substantially recovered following Ca readmission. ATP and creatine phosphate contents decreased during the Ca‐induced contraction, but recovered partially during the subsequent relaxation in Ca‐free solution. The effects of glucose removal were rapidly reversed when glucose or beta‐hydroxybutyrate (beta‐HB) were readmitted to the bathing solution. In the absence of Ca, readmission and removal of the substrates produced an insignificant change in O2 consumption, but the next Ca contraction was potentiated, the effect being stronger with glucose than beta‐HB. When the tonic contraction evoked by 2.4 mM‐Ca readmission had been abolished in glucose‐free, high‐K solution, a rise of the external Ca concentration to 10 mM, or 5 microM‐carbachol, still produced a transient contraction. This suggests that the tonic contraction has disappeared partially because of diminished Ca influx. In glycogen‐depleted preparations, the depolarization caused by carbachol, or by 20 mM‐K, was increased and spike discharge initiated when glucose was readmitted.(ABSTRACT TRUNCATED AT 250 WORDS)