bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms involved in irreversible anoxic damage to the in vitro rat hippocampal slice
Authors: Kass Ira S. , Lipton Peter
Published: December 2014

1. We have studied the effects of anoxia on the recovery of neural transmission between the perforant path and the dentate granule cells in the in vitro rat hippocampal slice. There is almost no recovery of the evoked population spike following 10 min of anoxia in slices from adult rats.

2. A 2 h exposure of slices to creatine markedly improves the recovery of the population spike (80% vs. 5%). The creatine pre‐incubation builds up phosphocreatine levels in the slice and prevents the large fall in ATP during anoxia; ATP falls to 7·9 rather than 3·6 nM/mg protein. The intracellular pH of both groups falls to the same level during anoxia.

3. If calcium concentration in the medium is reduced to 0 while magnesium concentration is raised to 10 mM during anoxia the evoked response recovers to about 65%.

4. The data suggest that an attenuation of the fall in ATP or entry of calcium during anoxia protects the tissue against irreversible transmission damage. Thus both of these factors participate in the generation of this damage. It is not yet clear if they act independently or if one acts by altering the other.

5. In the post‐anoxic recovery period the intracellular concentration of potassium is reduced by about 25%. However, it is still much higher than in slices that show only partial block of the evoked response when treated with ouabain. Therefore a fall in intracellular potassium 1 h after anoxia cannot explain the lack of recovery of the evoked response in adult tissue.

6. ATP levels in the post‐anoxic recovery period are reduced from their pre‐anoxic levels (9·7 vs. 13·9 nM/mg protein). However when azide or antimycin A are used to directly reduce ATP to the level found 1 h after anoxia the evoked response is reduced by only about 45%. Thus the reduced post‐anoxic ATP levels are not sufficient to explain the loss of the evoked response in adult tissue.

7. The data show that the irreversible loss of transmission is not due to decreased cell ATP or to decreased cell K/Na levels 1 h after the anoxic period.

8. Since creatine pre‐incubation protects against irreversible transmission loss this compound or one closely related to it may prove useful in attenuating irreversible brain damage in situ.
Catecholamine synthesis in rabbit carotid body in vitro
Authors: Fidone S. , Gonzalez C.
Published: December 2014

1. Catecholamine synthesis in rabbit carotid body was studied in vitro using [3H]DOPA and [3H]tyrosine as precursors. The effects of sympathectomy and transection of the carotid sinus nerve on [3H]dopamine ([3H]DA) and [3H]noradrenaline ([3H]NA) synthesis were investigated in chronically denervated carotid bodies.

2. When [3H]DOPA was used as precursor, the synthesis of [3H]DA was linear for more than 6 hr. The carotid body synthesized larger amounts of [3H]catecholamines than when [3H]tyrosine was used as precursor, but most of this excess was liberated into the incubation media. Using 10 μM‐[3H]DOPA as precursor, the synthesis rates were 6·76 and 1·51 n‐mole/g per hr for [3H]DA and [3H]NA, respectively; with 40 μM‐[3H]DOPA, these values increased to 19·22 and 3·23 n‐mole/g per hr, respectively.

3. The relationship between [3H]DOPA concentration and [3H]DA synthesis was linear throughout the range 5‐40 μM‐[3H]DOPA.

4. Sympathectomy reduced the synthesis of [3H]NA by 90% and [3H]DA by 37% when [3H]DOPA was used as precursor.

5. When [3H]tyrosine (40 μM) was used as precursor, synthesis of [3H]catecholamines was linear for at least 4 hr, with rates of 12·10 and 0·85 n‐mole/g per hr for [3H]DA and [3H]NA, respectively.

6. [3H]DA and [3H]NA synthesis from [3H]tyrosine exhibited the characteristics of saturable processes, with Km values of 16·8 and 17·6 μM, respectively.

7. 6‐methyltetrahydropterine (6‐MPH4, 100 μM), a synthetic analogue of the natural co‐factor for tyrosine hydroxylase, increased [3H]DA and [3H]NA synthesis from [3 H]tyrosine in both the carotid body and superior cervical ganglion, with the greatest effect seen in the carotid body.

8. When [3H]tyrosine was used as precursor, sympathectomy of the carotid body reduced [3H]NA synthesis by 80%, but did not alter [3H]DA or [3H]tyrosine levels in the tissue. Transection of the carotid sinus nerve had no effect on [3H]catecholamine synthesis in the carotid body.
Ions and water in the epithelial cells of rabbit descending colon.
Authors: Macknight A D , Mason D R , Rose R C , Sherman B
Published: December 2014

1. Isolated sheets of rabbit descending colon epithelial cells stripped from their underlying muscle coats were incubated in chambers at 37 degrees C with oxygenated media, and their non‐inulin space water, sodium, potassium and chloride contents were subsequently determined. 2. With sodium Ringer bathing both surfaces, amiloride, 10(‐4) M, decreased non‐inulin space sodium content by 76 mmol/kg dry wt. Ouabain, 10(‐3) M, caused loss of non‐inulin space potassium which was not completely compensated for by uptake of sodium over 30 min incubation. Chloride and water, therefore, decreased. Amiloride, 10(‐4) M, inhibited but did not prevent this uptake of sodium after ouabain. 3. Tissues exposed to sodium‐free choline Ringer rapidly exchanged non‐inulin space sodium for choline and, more slowly, lost potassium, chloride and water. The equilibration of sodium in the non‐inulin space when sodium Ringer was restored to the mucosal medium alone was largely amiloride‐insensitive. For restoration of non‐inulin space potassium to normal levels, sodium was required in the serosal but not the mucosal medium. 4. Neither the absence of glucose nor the absence of chloride from the mucosal medium affected the non‐inulin space sodium content when sodium was restored to the mucosal medium bathing sodium‐depleted tissues. 5. It is argued that, whereas non‐inulin space potassium and water contents are synonymous with their cellular values, only about one third of non‐inulin space sodium is cellular when sodium Ringer bathes both surfaces, and the concentration of the sodium within the cellular transport pool approximated 20 mmol/kg H2O, consistent with estimates obtained from other techniques.
Muscarinic agonists inactivate potassium conductance of guinea‐pig myenteric neurones.
Authors: Morita K , North R A , Tokimasa T
Published: December 2014

1. The effects of muscarinic agonists applied both by perfusion and ionophoresis to myenteric neurones of the guinea‐pig ileum were investigated by intracellular recording methods. 2. Perfusion with muscarinic agonists (acetylcholine, oxotremorine, methacholine, bethanechol) in concentrations of 100 nM to 10 microM caused membrane depolarizations. Brief ionophoretic applications of oxotremorine, or acetylcholine in the presence of hexamethonium, evoked depolarizations with a latency of 100 ms to 1 s and a duration of 5‐60 s. 3. The depolarizations were completely antagonized by low concentrations (1‐10 nM) of the muscarinic antagonists hyoscine or atropine. 4. The latency and time course of the muscarinic depolarizations were about one thousand times longer than those of nicotinic responses evoked in the same cell by acetylcholine applied from the same ionophoresis electrode. 5. The muscarinic depolarization was associated with a conductance decrease and reversed polarity at a membrane potential close to the potassium equilibrium potential. 6. The muscarinic depolarization became smaller but did not disappear completely during prolonged (up to 60 min) perfusion or repeated (more than 0.02 Hz) ionophoretic applications of muscarinic agonists. 7. Lower concentrations (3‐30 nM) of oxotremorine, which did not change membrane potential, reduced the amplitude and duration of the calcium‐dependent increase in potassium conductance which follows a burst of action potentials. 8. It is concluded that the muscarinic depolarization of myenteric neurones is due to potassium inactivation.
Relaxing and metabolic inhibitory action of X537A (Lasalocid) on the taenia of the guinea‐pig caecum.
Authors: Ishida Y , Shibata S
Published: December 2014

1. In the isolated guinea‐pig taenia, application of X537A to the muscle caused a relaxation, while A23187 caused a sustained contraction. 2. Treatment with adrenergic blocking agents and tetrodotoxin had no effect on the relaxing response to X537A. 3. In the presence of a low concentration (10(‐6) M) of X537A or under hypoxic conditions (bubbled with 95% N2: 5% CO2), the taenia lost the ability to respond to a high concentration (40 mM) of potassium with a sustained tonic contraction, although the rapid phasic contraction was still present. 4. When a low concentration of X537A was applied the shape of the contractile response to A23187 was changed from a sustained development of tension to an oscillatory tension which was also observed under hypoxia. 5. In tissues treated with glycerol for 3 weeks, neither X537A nor A23187 had any effect on the contractile response induced by elevation of calcium concentration (pCa = 4) in the presence of magnesium and ATP. 6. Exposure to a low concentration (10(‐6) M) of X537A, or hypoxia, slightly yet significantly decreased the ATP content of the muscle. A high concentration (10(‐5) M) of X537A markedly decreased the ATP content to about half normal. A23187 did not alter the ATP content. 7. Application of X537A did not alter the calcium content of the muscle and inhibited the A23187‐induced increase in content. Under hypoxia, A23187 failed to increase the calcium content of the muscle. 8. The results indicate that, in contrast to A23187, X537A has a relaxing and metabolic inhibitory action on the guinea‐pig taenia. The action of low concentrations of X537A resembled that of the hypoxia, indicating that X537A might exert its relaxing action, at least in part, by inhibition of aerobic energy metabolism of the muscle.
The effects of papaverine on the electrical and mechanical activity of the guinea‐pig ureter.
Authors: Brading A F , Burdyga T V , Scripnyuk Z D
Published: December 2014

1. The effects of papaverine (10(‐5)‐2 X 10(‐4) M) were studied on the evoked electrical and mechanical activity of the guinea‐pig ureter smooth muscle. In normal conditions the action potential consists of an initial spike followed by further spikes superimposed on a plateau phase. Papaverine reversibly decreased the duration of the plateau of the action potential, blocked the associated spikes, greatly reduced the amplitude of the contraction but enhanced the initial component of the action potential. 2. Papaverine did not change the membrane potential and had little effect on the membrane resistance. 3. Tetraethylammonium (5 mM), which blocks the delayed outward K current, did not prevent the decrease in the duration of the plateau nor the decrease of the contractile response caused by papaverine. 4. In Na‐free solution the duration of the action potential was decreased until only a single spike was seen, due to suppression of the plateau. An effect of papaverine could not be observed under these conditions. 5. Mn2+ ions (1 mM) completely suppressed the spike component and tension while the plateau component was substantially increased. Papaverine in the presence of Mn2+ reversibly blocked the generation of the action potential. When Mn2+ ions were added to Na‐free solution the duration as well as the amplitude of the spike was increased. Again, papaverine reversibly blocked the generation of the action potential. 6. Noradrenaline (10(‐4) M) and histamine (10(‐5) M) in normal conditions prolonged the duration of the action potential plateau and increased both the duration and amplitude of the concentration. Papaverine again blocked the plateau and greatly reduced the contractile response. 7. Papaverine caused the relaxation of KCl‐induced contractures, preferentially blocking the tonic component. 8. It is suggested that the inhibitory action of papaverine on ureter smooth muscle results from its specific blockade of the ‘slow’ Na/Ca channels responsible for the generation of the plateau component of the action potential.
The effect of a natriuretic atrial extract on renal haemodynamics and urinary excretion in anaesthetized rats.
Authors: Borenstein H B , Cupples W A , Sonnenberg H , Veress A T
Published: December 2014

1. An extract of cardiac atrial tissue, when injected intravenously into anaesthetized rats, caused a large and rapid increase in renal excretion of sodium chloride. 2. The renal response to atrial extract was associated with increases in total and medullary blood flow in the kidney, as measured by microsphere and albumin uptake methods, respectively. 3. The data suggest that these changes in renal haemodynamics may contribute to, but are unlikely to be the complete cause of, the natriuresis and chloriuresis following injection of atrial tissue extract.
The effects of injection of calcium ions and calcium chelators on calcium channel inactivation in Helix neurones.
Authors: Plant T D , Standen N B , Ward T A
Published: December 2014

1. The effects of intracellular injection of Ca, EGTA and EGTA/Ca buffers on inward currents flowing through the Ca channel in Helix aspersa neurones were studied under voltage clamp. 2. Inward currents were reversibly reduced by Ca injection. The extent of the reduction was dependent on the size and duration of the injection. Recovery from injection was exponential with a time constant around 18 s at 18‐20 degrees C. 3. In our salines, which contained tetraethylammonium chloride and 4‐aminopyridine, no outward current was activated by Ca injection at the holding potential. A given Ca injection reduced the inward current by the same fraction in 25 mM‐ and 2 . 5 mM‐Sr and also at different test potentials. We conclude that Ca injection does not activate an outward current. 4. Mean resting ionized internal Ca concentration, [Ca]i, measured with a Ca‐sensitive electrode was 1.9 X 10(‐7) M. Our injections increased this by less than 10(‐5) M, as expected if most of the injected Ca is bound. Constant‐field or Eyring rate theory considerations suggest that this rise in [Ca]i would not significantly affect the inward current through open Ca channels and we conclude, therefore, that Ca injection causes Ca channel inactivation. 5. The effect of Ca injection was blocked by prior injection of EGTA. Extracellular application of carbonyl cyanide m‐chlorophenylhydrazone increased the effect of Ca injection. 6. Ca injection does not inactivate Ca channels by lowering pHi since large H+ injections only caused small irreversible decreases in inward current. 7. EGTA injection increased peak Ca current (ICa) by around 30% and decreased the rate and extent of inactivation. Some inactivation remained, however, even after maximal EGTA injections. 8. Injection of EGTA/Ca buffers with free [Ca] less than 1.8 X 10(‐7) M increased peak ICa, while buffers with free [Ca] greater than 8.9 X 10(‐7) M decreased ICa. 9. Our results support the suggestion that Ca ions cause Ca inactivation by binding to a site which is accessible from the inside of the cell, and also suggest that there is some steady‐state inactivation present at physiological [Ca]i. A simple model is presented which describes the decline of Ca current in terms of Ca binding to a site accessible from the cytoplasm.
Cellular adaptation of amino acid transport following intestinal resection in the rat.
Authors: Menge H , Sepúlveda F V , Smith M W
Published: December 2014

1. The ability of rat ileal enterocytes to take up alanine and lysine before and after proximal resection of the small intestine has been assessed using both autoradiographic and dual‐isotope methods of analysis. 2. The length of individual villi was approximately doubled after resection. Alanine uptake measured in the presence or absence of Na, represented per cm2 mucosal surface area, decreased following intestinal resection. 3. Alanine and lysine uptake were confined to villus tip enterocytes in both control and ileal remnants. The net effect of intestinal resection was to increase amino acid uptake calculated per individual villus or per unit length of intestine. 4. Adaptational changes occurring as a result of resection included a shortening of the time needed for enterocytes to reach the stage where they first began to absorb amino acids and a doubling of the rate at which absorption increased during the later stages of enterocyte differentiation. 5. It is suggested that the physiological response to intestinal resection can best be appreciated by studying events taking place within individual enterocytes. The way in which adaptational changes become organized within the mucosa remains to be elucidated.
Bicarbonate effects, electromotive forces and potassium effluxes in rabbit and guinea‐pig gall‐bladder.
Authors: Cremaschi D , Meyer G , Rossetti C
Published: December 2014

The stimulating effect of external HCO3‐ on Na+ salt transport has been examined in rabbit and guinea‐pig gall‐bladder by electrophysiological methods, as a sequel to a previous study carried out by radiochemical techniques. At steady state, cell K+ activity was found to be significantly reduced in the presence of HCO3‐, whereas cell Na+ activity significantly increased; in parallel the apical membrane p.d. was depolarized; K+ equilibrium potential was higher than membrane p.d. in every case. The apical p.d. dependence on K+ was unaffected by HCO3‐, but in the guinea‐pig it was affected by Cl‐. Rapid increases in HCO3‐ concentration on the luminal side caused a depolarization of the apical p.d. of the guinea‐pig within about 30 sec, an effect that did not occur if the tissue was pre‐treated with 10(‐4) M‐acetazolamide; the epithelial resistance and apical/basolateral resistance ratio were unchanged in all cases. The primary action of HCO3‐ is confirmed to be on the apical membrane; an HCO3‐ conductance does not seem to be present at this level, either in the rabbit or guinea‐pig, nor does HCO3‐ affect Na+ influx through the apical conductive pathway, so that all the stimulating effects of the anion are confirmed to be on the neutral transports of Na+ salts; in spite of this, the apical electromotive force is modified due to the changed cell K+ activity. The rapid depolarization caused by the anion in the guinea‐pig is in agreement with an HCO3‐ electrogenic secretion and/or a basolateral conductance for the anion. Polyelectrolyte dissociation from protons increases in the absence of external HCO3‐: the negative charges are mainly counterbalanced by bound Na+ in the rabbit and by free K+ in the guinea‐pig. K+ leakage from the cell into the lumen is calculated to be minimal in the rabbit and all K+ lost could be reabsorbed through the paracellular pathways; K+ efflux to the subepithelial layer via conductive routes is insufficient to account for the over‐all K+ efflux.
Fast inward‐rectifying current accounts for anomalous rectification in olfactory cortex neurones.
Authors: Constanti A , Galvan M
Published: December 2014

The somatic membrane of guinea‐pig olfactory cortex neurones in vitro (23 degrees C) was voltage clamped by means of a single‐micro‐electrode sample‐and‐hold technique. In most cells the current‐voltage (I‐V) relationship showed inward (anomalous) rectification with increasing hyperpolarization beyond the resting potential (ca. ‐80 mV). Under current‐clamp conditions a time‐dependent ‘sag’ of the hyperpolarizing electrotonic potentials was observed following an initial overshoot. No depolarizing after‐potential was seen on return to the resting potential. Inward rectification was activated between ‐100 and ‐110 mV (irrespective of pre‐set resting potential) and increased the membrane input conductance by up to three‐fold. The rectification was unaffected by tetrodotoxin or Cd2+. Under somatic voltage clamp, hyperpolarization beyond ‐110 mV activated a rapid inward relaxation fitted by a single exponential. The relaxation time constant (tau on) decreased e‐fold for a 40 mV hyperpolarization. (Typical values: 28 ms at ‐110 mV declining to 13 ms at ‐140 mV; external K+ concentration 3 mM, 23 degrees C). More extreme hyperpolarizations evoked a slower ‘inactivation’ phase (tau = 40‐60 ms). A transient outward‐decaying ‘tail’ current reflecting deactivation of inward rectification was seen on stepping from ‐140 mV to more positive potentials. tau off became slower with hyperpolarization. The tail current disappeared at a potential close to the expected VK but was rarely inverted to an inward‐decaying tail. It is proposed that the fast inward‐rectifying current of olfactory neurones (If.i.r.) is a K+ current analogous to the anomalous K+ rectifier of marine egg and frog muscle membranes. The behaviour of the inward rectifier was dependent on external K+ concentration in accordance with the unique ‘V‐‐VK’ dependence of classical anomalous rectification; however, of several agents tested (external Cs+, Ba2+, Rb+, Tl+ or tetraethylammonium), only Cs+ and Ba2+ blocked If.i.r. in a time‐ and voltage‐dependent manner. The effect of tetraethylammonium resembled that of an increase in external K+. The possible contribution of the inward rectifier to the passive cell membrane properties is discussed.
Structure‐activity relationships for some substance P‐related peptides that cause wheal and flare reactions in human skin.
Authors: Foreman J C , Jordan C C , Oehme P , Renner H
Published: December 2014

Substance P (6.25‐25 p‐mole) produced dose‐dependent flare and wheal responses when injected intradermally into the volar surface of the human forearm. The maximum flare response was obtained within the first 3 min of injection and declined thereafter. The wheal response reached a maximum after 12 min following the injection. Only those peptides having one or more basic residues in the N‐terminal region were effective in producing a flare reaction. Eledoisin‐related peptide and SP1‐9 were 17 and 7 times less active than substance P respectively, whilst [D‐pro2, D‐phe7, D‐trp9]SP1‐11 was twice as active. The N‐terminal tetrapeptide, SP1‐4 and eledoisin were inactive in the dose range tested. Wheal‐producing activity was not dependent on the presence of basic residues and the rank order of relative potencies was: physalaemin (2.0): [D‐pro2, D‐phe7, D‐trp9]SP1‐11 (1.1): SP1‐11 (1.0): SP4‐11 (0.4): SP1‐9 (0.15): eledoisin‐related peptide (0.08): eledoisin (0.06). The N‐terminal tetrapeptide failed to produce a wheal response in the dose range tested. Substance P was approximately equi‐active with poly‐L‐arginine in the production of wheal and flare and both of these agents were about 10 times more potent than histamine. Adenosine triphosphate (25‐400 n‐mole) produced dose‐dependent wheal and flare responses and was 10,000 times less potent than substance P. Pre‐treatment of the subjects with the H1 histamine antagonist, chlorpheniramine, (20 mg I.V.) reduced the wheal and flare responses to substance P. Local anaesthetic injection into the skin reduced the spread of the flare response but did not affect the development of the wheal response. Pre‐treatment of the skin with capsaicin reduced the flare but not the wheal response to intradermal injection of histamine. The results are discussed in relation to the mechanism of the ‘axon reflex’ vasodilatation in skin. This is thought to involve mast cells in addition to substance P‐containing primary afferent neurones.
Detections of movements imposed on finger, elbow and shoulder joints.
Authors: Hall L A , McCloskey D I
Published: December 2014

The angular displacements necessary for 70% correct detection were determined in normal subjects at the shoulder and elbow joints and at the terminal joint of the middle finger. Angular velocities of displacement between 0.125 degrees and 160 degrees/s were tested. Each joint was tested in the mid‐range of its normal excursion. The joints were carefully supported for testing and the muscles acting at the joints were relaxed. When assessed in terms of angular displacements and angular velocities, proprioceptive performance at the shoulder and elbow joints was superior to that at the finger joint. Optimal performance at the finger joint was attained over the range of angular velocities from 10 degrees to 80 degrees/s. Optimal performance at both more proximal joints was optimal over a wider range (2 degrees‐80 degrees/s). Active pointing movements made without vision of the moving part were performed at each joint at velocities within the range of optimal proprioceptive performance. However, when detection levels and displacement velocities were expressed in terms of linear displacements and velocities at the finger tip for all three joints, the finger joint gave the best performance and the shoulder the worst. In practical terms, therefore, displacements of a given linear extent are best detected if they move distal joints and worst if they move proximal joints. For the elbow and finger joints the detection level and velocity data were expressed also in terms of proportional changes in the lengths of muscles operating at these joints, and as proportional changes in the distance between the points of attachment of the joint capsules. Analysis in terms of proportional changes of muscle length showed remarkably similar performance levels at both joints. This suggests that intramuscular receptors are important determinants of proprioceptive performance. Analysis in terms of joint capsular displacement did not unify the data: on this form of analysis proprioceptive performance at the elbow joint was superior.
The maturation of cutaneous reflexes studied in the upper limb in man.
Authors: Issler H , Stephens J A
Published: December 2014

Cutaneous reflex responses have been recorded from forearm flexor and extensor muscles following electrical stimulation of the fingers. Recordings have been made from premature infants, term infants and children between the age of 6 weeks and 11 years. In the new‐born, stimulation of the fingers elicits such a powerful reflex that, in general, individual stimuli will evoke a reflex synchronous action potential in both forearm flexor and extensor muscles. Individual stimuli delivered to the fingers also elicit reflex synchronous muscle action potentials in forearm flexor and extensor muscles in patients with clinical signs of upper motor neurone lesion affecting the upper limb; this has not been observed in normal adult subjects. The latency of the reflex response in the term infant is about 18 msec. Comparison of this value with the latency of the tendon jerk for these muscles would indicate a central delay for the cutaneous reflex of about 3 msec. The latencies of the cutaneous reflex and tendon jerk remain constant over the first 5 years of life. The size of the short‐latency cutaneous reflex response decreases progressively over the first year of life. In the second year of life stimulation of the fingers produces long‐ as well as short‐latency increases in recorded muscle electrical activity. The maturation of the cutaneous reflex response is discussed in terms of the maturation of function of the corticospinal tract.
Ionic mechanisms involved in the strontium‐induced spike and plateau in the smooth muscle of rat portal vein.
Authors: Hotta K , Yamamoto Y
Published: December 2014

The action of Sr on the smooth muscle of rat portal vein was studied electrophysiologically using micro‐electrodes. By replacing Ca with Sr (2.5 mM), the spontaneous membrane activity was altered and spikes were followed by a long lasting plateau potential. The mechanisms which generated the spike and the plateau in the Sr‐induced activity were elucidated. As the concentration of Sr was increased, the peak potential and the maximum rates of rise and fall of the initial spike in each discharge increased. The peak potential varied by 15.2 mV with a 10‐fold change in [Sr]o. As there was a decrease in the membrane resistance during the plateau, an increase in the permeability of the membrane for Sr, Cl or Na could be responsible for generation of the plateau. The amplitude of the plateau decreased with increase in the concentration of Sr, remained unchanged in a low‐Cl solution, but was diminished in a low‐Na solution. Mn (1‐2 mM) inhibited not only the spike but also the plateau. TEA (20 mM) shifted the plateau potential in a positive direction and the plateau became permanent. When inward currents were applied in the presence of TEA, spikes with large overshoots and small rates of fall were induced. These results indicate that Sr and K conductances of the membrane generate the spike and that slow‐inactivating voltage‐dependent Na conductance produces the plateau.
On the site of impulse initiation in a neurone.
Authors: Moore J W , Stockbridge N , Westerfield M
Published: December 2014

In the preceding paper (Moore & Westerfield, 1983) the effects of changes in membrane properties and non‐uniform geometry on impulse propagation and threshold parameters were investigated. In this paper the contributions of these and other parameters to the site of initiation of an impulse were determined by computer simulations using the Hodgkin‐Huxley membrane description, the cable equations, and geometry appropriate for a simplified motoneurone with a non‐myelinated axon. Antidromic invasion of action potentials into the soma was found to depend upon (a) the ionic channel rate constants (determined by the temperature), (b) the abruptness of the transition from the small‐diameter axon to the larger diameter (and increased load) of the soma‐dendrite, (c) extensions of active properties into the dendrite, and (d) density of ion channels. The location of the apparent site of initiation of impulses was not necessarily at the site of synaptic input nor the nearest active membrane. Its position depended upon (a) the fraction of the dendritic tree with excitable membrane, and secondarily on (b) the stimulus strength. Even with uniform excitability in the active membrane, the apparent site of initiation could be moved a considerable distance from the soma and the site of stimulation by appropriate choice of the various parameters noted above.
Effects of low temperature and terminal membrane potential on quantal size at frog neuromuscular junction
Authors: Cohen I. S. , van der Kloot W.
Published: December 2014

1. Two mechanisms proposed for the quantal release of acetylcholine (ACh) are: (i) that the quanta are pre‐packaged in vesicles and released by exocytosis and (ii) that the ACh is released from the cytoplasm of the nerve terminal by the opening of an ACh channel. Our experiments were designed to test aspects of these hypotheses.

2. Miniature end‐plate currents (m.e.p.c.s) were reversibly decreased in amplitude and increased in duration as the temperature was decreased between 15 and 6 °C. The amplitude decreased with a Q10 of 2·4 between 15 and 11 °C, and then with a Q10 of 3 between 11 and 6 °C. The half‐decay time increased with a Q10 between 4 and 5 over the entire temperature range.

3. The effect of temperature on the end‐plate current (e.p.c.) in response to ionophoretically applied ACh was also studied. The e.p.c. in response to a set, sustained dose of ACh was 30% larger at 11 °C than at 15 °C, and about 10% larger at 6 °C than at 15 °C.

4. The difference in the end‐plate response to brief pulses of ACh (m.e.p.c.s) and to sustained application of ACh was analysed by Dionne & Stevens (1975). The amplitude of the sustained response depends on both the number of channels opened in the end‐plate, and the length of time they stay open. When our temperature data are analysed in this way, it appears that the amount of ACh/quanta acting on the end‐plate is altered by less than 25% over the temperature range 15‐6 °C.

5. From the experiments in which the nerve terminal membrane potential was shifted by external currents it was concluded that miniature end‐plate potential amplitude was independent of the terminal membrane potential (Cooke & Quastel, 1973). This conclusion was confirmed by measuring m.e.p.c.s in low Ca2+ Ringer solution containing 2·0 and 22·0 mM‐KCl; there was no consistent change in m.e.p.c. amplitude.

6. The effects of both temperature and terminal membrane potential are more readily interpreted by the vesicle than by the channel hypothesis, since for the channel hypothesis the duration of channel opening should be temperature‐sensitive and the efflux of ACh+ through the terminal membrane should be potential‐dependent.
Electrical coupling between ventricular paired cells isolated from guinea‐pig heart.
Authors: Kameyama M
Published: December 2014

Guinea‐pig hearts were digested enzymatically, resulting in aggregates of cells, cell pairs and single cells. Pairs of cells were chosen for measurement of coupling resistance (rj). Current was injected into one cell of a cell pair. The ratio of the resulting voltage change of the other cell to that of the injected cell was more than 0.8 in most cells (tight electrical coupling) or near 0 in a few cells (functional isolation). rj was affected neither by the transjunctional current, nor by the membrane potential itself. On the other hand, either a reduction of external Na+ concentration (15‐60 mM), or an application of ouabain or strophanthidin (10(‐5) M) produced a significant increase in rj. It is concluded that low‐resistance cell‐to‐cell junctions are functionally preserved in pairs of dissociated ventricular cells, that the junctional membrane shows no detectable rectification and that intracellular Ca2+ reduces the junctional conductance.
The ionic basis of adenosine receptor actions on post‐ganglionic neurones in the rat.
Authors: Henon B K , McAfee D A
Published: December 2014

Adenosine inhibited three Ca2+‐dependent potentials recorded intracellularly from post‐ganglionic neurones of the rat superior cervical ganglion. A shoulder on the falling phase of the action potential elicited in normal Locke solution, a hyperpolarizing after‐potential (h.a.p.) that follows the spike, and a regenerative Ca2+ spike elicited in Locke solution containing TTX and TEA were all reversibly inhibited by adenosine analogues in a dose‐dependent fashion. The maximum rate of rise of the Ca2+ spike (dV/dt) was markedly reduced suggesting that the underlying mechanism of adenosine action is inhibition of the Ca2+ conductance mechanism and thus, the voltage‐sensitive Ca2+ current. I/V curves in low Ca2+, high Mg2+, TTX, TEA, and Co2+ to block the Ca2+ current show no change in resistance in the presence of 2‐chloroadenosine. The actions of adenosine were nearly eliminated in the presence of 1 mM‐theophylline, an adenosine receptor antagonist. The order of agonist potency on the inhibition of the h.a.p. was: N‐6‐[L‐phenylisopropyl] adenosine (L‐PIA) greater than 2‐chloroadenosine greater than adenosine greater than cyclic AMP = 5' AMP. The concentration of L‐PIA which produced a half‐maximal effect (EC50) was 0.5 microM and that for cyclic AMP was 100 microM. Dipyridamole, an adenosine uptake blocker, potentiated the effects of low concentrations of adenosine and shifted the dose‐response curve for adenosine towards that of 2‐chloroadenosine (EC50 = 1 microM). These results are consistent with the concept of an external adenosine receptor, but we are unable to assign a receptor subtype. Cyclic AMP mimicked the effects of adenosine, but these effects were eliminated by adenosine deaminase. Our results suggest that the electrogenic effects of bath‐applied cyclic AMP may result from the metabolism of cyclic AMP to adenosine by ganglionic tissue. We conclude that adenosine activates a receptor on the neuronal cell surface to inhibit the voltage‐dependent Ca2+ current.
Influence of luminance gradient reversal on simple cells in feline striate cortex
Authors: Hammond P. , Mackay D. M.
Published: December 2014

1. The sensitivity of simple cells to luminance gradient reversal in bar stimuli has been investigated in the striate cortex of lightly anaesthetized cats.

2. The influence of segment(s) of one polarity of contrast, partially masking or added end‐on to a bar of reversed contrast, was assessed against a stationary textured background (of intermediate average luminance), which was itself without influence on cell behaviour.

3. In either configuration, short segments of reversed contrast were suppressive of bar response, to an extent varying with location along the receptive‐field axis, but much greater than predictable from length‐summation characteristics. Response suppression, even by very short segments, was often total.

4. The effects of longer segments, added end‐on to a bar of opposite contrast, depended on the extent of length summation exhibited by each cell. With progressive extension of these segments, some recovery of response occurred in a few simple cells with larger receptive fields, but not in small‐field simple cells. The behaviour of end‐stopped simple cells was comparable in all respects to that of their end‐free counterparts, within the length‐summation zone; thereafter, invasion of the inhibitory end‐zones by bars of either polarity elicited a generalized decline in response.

5. Where responsiveness was restored by adding longer segments of opposite polarity, the response peak shifted to the discharge centre appropriate to that polarity.

6. All these results were found with either polarity of contrast, i.e. a light bar plus dark segments or the converse.

7. Similar results were obtained for motion in either direction across the receptive field; and also for flash‐presentation, over either the centre or flanks (whether ‘on’ or ‘off’) of the receptive field.

8. The effectiveness of contrasting added segments was assessed as a function of location along the receptive‐field axis for flash‐presented and for moving stimuli. Suppressive effects were greatest over the centre of the receptive field, declining progressively in either direction along its axis, but over greater distances than anticipated from length summation.

9. None of the results presented could have been predicted from length‐summation characteristics. They are strongly suggestive of gating, rather than linear, antagonistic interactions.
The influence of rod light and dark adaptation upon rod‐cone interaction.
Authors: Bauer G M , Frumkes T E , Holstein G R
Published: December 2014

The influence of a rod‐detected mask of illuminance IR on the threshold illuminance of a cone‐detected test flash (ICth) was assessed while rods were recovering from the effects of a bleach, and when rods were selectively light adapted. Providing that IR was restricted to within 2 log10 units of rod mask threshold (IRth), results show that ICth/IC0 = K (square root (IR/IRth) + D), where IC0 is cone absolute threshold, D is a dark noise term and K is a proportionality constant. These data were used to obtain 'equivalent background functions' or 'Crawford (1947) transforms' (illuminance of a background field plotted against time in the dark). The same Crawford transform was obtained when either IRth or ICth (in the presence of a fixed illuminance IR) were used as equating variables. All of the foregoing results could be predicted by considering both the influence of light adaptation on rods (see Fain, 1976) and the model developed by Bauer, Frumkes & Nygaard (1982). Under dark‐adapted conditions, 40' and 60' diameter rod masks of equal illuminance have very similar influences on ICth. When rods are selectively light adapted 60' masks have smaller influences on ICth. The foregoing results were used to extend the model developed in the previous paper. We suggest that rod adaptation has a distinct influence on neural loci designated E (the excitatory spatial summator) and I (the inhibitory spatial summator), and that E represents a site for both adaptation and spatial summation.
Kinetic analysis of atropine‐induced alterations in bullfrog ganglionic fast synaptic currents.
Authors: Connor E A , Levy S M , Parsons R L
Published: December 2014

The concentration‐ and voltage‐dependent effects of atropine on the fast excitatory post‐synaptic current (e.p.s.c.) of bullfrog sympathetic ganglion cells have been analysed and fitted to a kinetic scheme of open‐channel blockade. Atropine (1‐75 microM) reduced the peak e.p.s.c. amplitude without altering the quantal content or the reversal potential. The e.p.s.c. decay was complex in the presence of atropine, being well fitted by two exponential components. With increasing concentrations of atropine the time constant of the fast component, tau 2, decreased and the time constant of the slow component, tau 1, increased. Over the voltage range ‐30 to ‐100 mV tau 2 exhibited little or no voltage dependence and tau 1 increased with hyperpolarization. The amount of charge moved during the e.p.s.c. was reduced as a function of atropine concentration. Driving functions, which represented the rate of channel opening, were derived from e.p.s.c.s both from control and atropine‐treated cells. The characteristics of the driving functions did not vary with membrane voltage, but the driving functions were shorter in duration from atropine‐treated than control cells. The area under the driving function decreased as a function of atropine concentration. The decay time constants and the amplitude ratio of the exponential components were used to calculate the closing, blocking, and unblocking rate constants, alpha, G, and F. alpha and F remained constant with increasing atropine concentration, but G declined significantly. The voltage dependence of the equilibrium constant, G/F, implied that the transient blocking site for atropine is halfway through the ionic channel. The sequential model does not predict the concentration‐dependent decrease in the blocking rate, G, or in the charge moved during an e.p.s.c. We conclude that atropine has an action more complex than simple channel blockade in sympathetic ganglion cells.
Hormone‐sensitive magnesium transport in murine S49 lymphoma cells: characterization and specificity for magnesium
Authors: Erdos Joseph J. , Maguire Michael E.
Published: December 2014

1. The hormone‐sensitive transport of Mg2+ into murine S49 lymphoma cells and its relationship to other divalent cation transport systems have been investigated.

2. Mg2+ influx, measured with 28Mg2+, is saturable with an apparent extracellular ion concentration at half‐maximal influx (Kin) for Mg2+ of 330 μM and a maximal influx rate of 360 p‐mole/min.107 cells (2·9 n‐mole/min.mg cell protein or a flux rate of about 0·12 p‐mole/sec.cm2). Efflux of Mg2+ is biphasic with half‐times of 55 and 240 min at 37 °C and is temperature‐sensitive.

3. β‐Adrenergic agonists inhibit influx but not efflux of Mg2+ in S49 cells. Efflux of Mg2+ is also unaffected by extracellular [Mg2+] or [Ca2+]. These results imply that the mechanism of the transport system does not involve Mg—Mg exchange.

4. Mn2+ is a non‐competitive inhibitor of Mg2+ influx with an inhibition constant, Ki, of about 200 μM. The weak inhibition exhibited by Ca2+ (Ki > 5 mM) is also non‐competitive. La3+ inhibits Mg2+ transport half‐maximally at about 100 μM; Ni2+, Zn2+, Co2+ and Sc3+ are all less effective than La3+. The Ca2+‐channel blockers cis‐diltiazem, verapamil, and nifedipine and the monovalent cations Na+ and K+ also have no effect on Mg2+ influx. However, increasing the extracellular pH stimulates Mg2+ influx.

5. Total cellular Mg2+ is about 85 n‐mole/107 cells; however, at apparent isotopic equilibrium with 28Mg2+ less than 3% of total cellular Mg2+ has been exchanged. This indicates that cellular Mg2+ is highly compartmented and that recently transported Mg2+ exchanges very slowly with bulk intracellular Mg2+.

6. Ca2+ influx has a Kin of 80 μM and is much slower than Mg2+ influx. Vmax varied in different experiments from 3 to 15 p‐mole/min.107 cells (25‐125 p‐mole/min.mg cell protein). Efflux of Ca2+ is biphasic with half‐times of 22 and 200 min and is temperature‐sensitive. Hormonal stimulation has no effect on either influx or efflux of Ca2+. Mg2+ is a competitive inhibitor of Ca2+ influx (Ki = 3 mM).

7. Two kinetic components of Mn2+ influx are present with apparent Kins of 4 μM and 100 μM. Maximal influx rates are 5 and 60 p‐mole/min.107 cells (40 and 480 p‐mole/min.mg cell protein), respectively. Influx of Mn2+ is not altered by β‐adrenergic agonist.

8. Uptake of Na+ or K+ is unaltered by β‐adrenergic stimulation.

These data in the S49 lymphoma cell indicate that (a) Mg2+ is translocated by a transport system independent of those that transport other divalent cations, (b) hormonal inhibition of divalent ion transport is specific for Mg2+ and (c) cellular Mg2+ is highly compartmented.
The kinetics and temperature dependence of the pace‐maker current if in sheep Purkinje fibres.
Authors: Hart G
Published: December 2014

The kinetic properties of the if channel in shortened sheep Purkinje fibres were investigated using a two‐micro‐electrode voltage‐clamp technique in the presence of Ba2+, Mn2+ and tetrodotoxin (TTX). The time course of the hyperpolarization‐activated if currents (DiFrancesco, 1981 b) at potentials within the activation range was found to depend on whether the channel was switching 'on' or 'off'. At potentials positive to the half‐activation point if decay was faster than if onset; at potentials negative to the half‐activation point if onset was faster than if decay. The time courses of if onset and decay become similar only at potentials close to the centre of the activation range. If a single exponential was fitted to the time course of if switching, the time constant (tau y) was found to vary as a function of potential from approximately 50 msec to several seconds. The tau y ‐ voltage relation is an extremely steep bell‐shaped distribution. Reducing external Na+ (range 140‐17.5 mM) did not alter the voltage dependence of the if time course. Increasing external K+ (range 5‐60 mM) shifted the if time constants and activation curve by similar amounts in a depolarizing direction. The temperature dependence of if was investigated over the range 27.5‐41 degrees C. Cooling reversibly slowed the time course of if activation with a Q10 of 3.13 (S.D. +/‐ 0.85, n = 62). A reversible reduction in the slope of the fully‐activated current‐voltage relation was observed on cooling, the Q10 being 1.35 (S.D. +/‐ 0.07), and was usually accompanied by a small depolarizing shift of the half‐activation point and the reversal potential Ef. It is concluded that the if time course shows a marked potential dependence and does not obey Hodgkin‐Huxley kinetics. Its temperature dependence resembles that of if in the sino‐atrial node (DiFrancesco & Ojeda, 1980).
The effects of motilin on periodic myoelectric spike activity in intact and transected canine small intestine.
Authors: Pinnington J , Wingate D L
Published: December 2014

The effects of motilin infusions on periodic myoelectric spike activity were studied in conscious dogs with an intact small intestine and in dogs with established jejunal Thiry‐Vella loops (T‐V loops). Myoelectric activity was recorded from chronically implanted electrodes on the intact intestine, the anastomosed intestine and on the jejunal T‐V loop. During fasting, migrating myoelectric complexes (m.m.c.s) were present in the intact and anastomosed intestine and in the T‐V loop; in the latter, intervals between m.m.c.s were significantly shorter (P less than 0.05). Infusion of motilin induced premature m.m.c.s in the intact and anastomosed intestine, reducing the interval between successive m.m.c.s (P less than 0.05). In contrast, in the T‐V loop, motilin significantly reduced the number of m.m.c.s (P less than 0.01) and the interval between two m.m.c.s was prolonged. After an infusion of motilin, the number of m.m.c.s in the intact and anastomosed intestine was significantly reduced (P less than 0.01), with a corresponding increase in the intervals between m.m.c.s; no further changes were observed in the T‐V loop. These results demonstrate that m.m.c.s are induced by motilin in the proximal gut, suggesting a humoral mechanism for m.m.c. initiation in this region. In contrast, the genesis of m.m.c.s in jejunal T‐V loops is delayed by motilin.