bluuebunny/crossref_metadata_2025 huggingface dataset:
The ionic selectivity and calcium dependence of the light‐sensitive pathway in toad rods.
Authors: Hodgkin A L , McNaughton P A , Nunn B J
Published: December 2014

A new method is described for determining the effects of rapid changes in ionic concentration on the light‐sensitive currents of rod outer segments. Replacing Na with another monovalent cation caused a rapid change in current followed by an exponential decline of time constant 0.5‐2 s. From the magnitude of the initial rapid change in current we conclude that Li, Na, and K and Rb ions pass readily through the light‐sensitive channel in the presence of 1 mM‐Ca, whereas Cs crosses with difficulty and choline, tetramethylammonium and tetraethylammonium not at all. The effect of reducing Ca in the external medium indicates that the residual inward current recorded for a few seconds when Na is replaced by an impermeant ion is carried largely by Ca ions. With 1 microM‐Ca in the external medium the relative ability of monovalent cations to carry light‐sensitive current is Li:Na:K:Rb:Cs = 1.4:1:0.8:0.6:0.15. The same order applied in the physiological region but the values are less certain. Large transient inward currents are seen if external Ca is raised form 1 microM to 5 mM or more; these currents which are maximal in an isotonic Ca solution are presumably carried by Ca. The effect of monovalent cations on the number of open light‐sensitive channels was tested by adding the cation to a solution containing 55 mM‐Na. Na ions open light‐sensitive channels with a delay, probably by promoting Na‐Ca exchange; K and Rb close channels by inhibiting exchange; Li and Cs seem inert in the exchange mechanism. The rate at which inward current declines in low [Na]o or high [Ca]o is accelerated by weak background lights and slowed by 3‐isobutyl‐1‐methylxanthine (IBMX), which inhibits the hydrolysis of cGMP. On returning to Ringer solution after a period in low [Na]o the current recovers with a delay of about 1 s which decreases as the Ca concentration of the low [Na]o medium is reduced. We conclude that intracellular Ca has a strong effect on the number of open light‐sensitive channels. None the less, several observations are inconsistent with channel closure being dependent simply on combination with internal Ca.
Mechanism of action of insulin on acetylcholine‐evoked amylase secretion in the mouse pancreas.
Authors: Singh J
Published: December 2014

The effects of insulin and acetylcholine (ACh) on amylase secretion, transmembrane movement of 45Ca2+ and K+, membrane potential and cyclic nucleotide levels in the isolated mouse pancreas were investigated. Insulin alone had no effect on either amylase secretion or 45Ca2+ fractional efflux but it markedly potentiated the ACh‐evoked amylase secretion and significantly reduced the ACh‐induced 45Ca2+ fractional efflux. These effects were dose related. Insulin evoked a small membrane hyperpolarization and an increase in K+ efflux. The islet hormone had virtually no effect on ACh‐induced membrane depolarization but it markedly enhanced the ACh‐elicited K+ efflux. Both insulin and ACh had marked time‐dependent effects on the metabolism of adenosine 3',5'‐cyclic monophosphate (cyclic AMP). Insulin increased and ACh decreased cyclic AMP concentration when applied separately. However, when added together, insulin and ACh caused a rapid and sustained elevation of cyclic AMP levels. Superfusion of mouse pancreatic fragments with an exogenous lipid‐soluble derivative of cyclic AMP (dibutyryl adenosine 3',5'‐cyclic monophosphate) caused dose‐dependent increases in amylase secretion. Dibutyryl cyclic AMP also markedly enhanced, in a dose‐dependent manner, the ACh‐evoked amylase secretion. It is concluded that insulin may exert its potentiating action on ACh‐evoked amylase output in the mouse pancreatic acinar cells by elevating both cytoplasmic Ca2+ and cyclic AMP levels.
The structure of the terminal arborizations of physiologically identified retinal ganglion cell Y axons in the kitten.
Authors: Friedlander M J , Martin K A , Vahle-Hinz C
Published: December 2014

Retinal ganglion cell (r.g.c.) axons (n = 17) in the optic tract of 4‐5 week‐old kittens and adult cats (n = 4, this study, n = 27 from other reports) were studied both physiologically and morphologically. Axons were initially classified during extracellular recording with a battery of physiological tests that included Fourier analysis of the response to a sinusoidally counterphased sine‐wave grating. Y axons had a significant second harmonic response component (greater than twice the fundamental) present independent of the spatial phase position of the grating. These axons were then recorded from intracellularly and subsequently filled ionophoretically with horseradish peroxidase (HRP). The HRP filled the axons' terminal arborizations in the dorsal lateral geniculate nucleus (l.g.n.). The innervation pattern and and structure of the terminal arborizations of the kitten r.g.c. Y axons were compared to those of the adult. The kitten Y axons innervated the l.g.n. in a pattern similar to that of the adult (individual branches from a single axon always innervated lamina A or A1 and may also have innervated lamina C, the medial interlaminar nucleus (m.i.n.) and/or sent branches that coursed medial to the l.g.n.). Fourteen of seventeen of these Y axons in the kitten innervated either of the A‐laminae heavily (greater than 200 terminal boutons per axon). The remaining three r.g.c. Y axons in the kitten had only small arborizations within lamina A (less than fifty terminal boutons per axon) but heavily innervated lamina C. The structure of the terminal boutons on the kitten r.g.c. Y axons was highly variable when compared to axons of adult cats. Some of the boutons were spherical or crenulated as in the adult. Many others had filopodia and growth cone‐like terminals with fine extensions. This variable maturation of terminal boutons was seen both between axons and on individual axons. The number of boutons on the kitten r.g.c. Y axons in the A‐laminae was significantly less than that of adult Y axons. The mean numbers of boutons per axon were 476 and 1553 in the kittens and adult cats, respectively (P less than 0.001, Mann‐Whitney U test). The width of the terminal arborization of individual Y axons in the A‐laminae of the kittens was considerably smaller than in adult cats (mean widths of the terminal arborizations are 192 and 293 micron in the kittens and adult cats, respectively).(ABSTRACT TRUNCATED AT 400 WORDS)
Electrical responses of smooth muscle cells of the rabbit ear artery to adenosine triphosphate.
Authors: Suzuki H
Published: December 2014

Ionophoretic application of ATP to smooth muscle cells of the rabbit ear artery produced rapid depolarization of the membrane and, in the case of large doses of ATP, spike potentials or slow oscillatory potentials. The ATP response desensitized rapidly, and required over 70 s for recovery. When the intervals between repetitive application of ATP were shorter than 70 s, the amplitudes of the ATP responses successively decreased. Ejection of ATP with increasing intensities of current (10‐15% of the first) was required to produce successively increasing amplitudes of ATP responses. Repetitive stimulation of perivascular nerves (at intervals of less than 10 s) evoked increasing amplitude of excitatory junction potentials (e.j.p.s). Quinidine (over 5 X 10(‐5) M) inhibited and theophylline (over 5 X 10(‐4) M) enhanced the ATP response, with associated depolarization or hyperpolarization of the membrane, respectively. Cocaine (over 10(‐6) M) depolarized the membrane and enhanced the ATP response. Phentolamine reduced the amplitude of the ATP response with no change in the membrane potential, only when the concentration was extremely high (over 10(‐4) M). These all therefore appear to represent non‐specific interactions with the effects of ATP. Bath application of ATP depolarized the membrane dose dependently and, at concentrations over 5 X 10(‐7) M, produced spike potentials. The amplitude of electrotonic potentials decreased during the ATP‐induced depolarization, thereby suggesting an increase in ionic conductance of the membrane. ADP depolarized the membrane, the effect being weaker than that of ATP. Both AMP and adenosine hyperpolarized the membrane. The results provide evidence that in the rabbit ear artery, the e.j.p. could be mimicked by ATP. ATP can however only account for the fast e.j.p. if it is released in increasing amounts with successive nerve discharges. Reported blocking agents for ATP receptors did not block the response to ATP in this tissue.
Changes in brain phosphorus metabolites during the post‐natal development of the rat.
Authors: Tofts P , Wray S
Published: December 2014

Changes in brain phosphorus metabolites during the post‐natal development of the rat and in neonatal and adult guinea‐pigs have been studied in vivo using 31P nuclear magnetic resonance spectroscopy (n.m.r.s.). The brain spectra showed clear differences with age, particularly during the first 3 weeks post‐partum. The spectra from 4‐day‐old rats resembled those of new‐born human infants. We suggest that the differences between human and animal brains seen in previously published spectra arise because of an age difference rather than a species difference. The phosphocreatine (PCr) to nucleoside triphosphate (NTP) ratio increased from around 1.0 in 3‐day‐old rats to 1.8 in adult animals. The adult ratio is larger than that previously reported from in vitro chemical analyses. An unknown compound in the phosphomonoester (PME) region of the spectra predominated in young animals, but decreased in concentration relative to NTP with age and reached adult values by around 2 weeks post‐partum. Neonatal guinea‐pigs, which are much more developed at birth than the rat, had a significantly greater PCr/NTP ratio than the neonatal rat, but their brain spectra also contained the large PME peak. The intracellular pH of cerebral tissue was estimated to be 7.21 +/‐ 0.02 and did not show any change with age. The changes we find in the phosphorus compounds in the brain may be of importance in post‐natal development, and the possible functional significance of these results is discussed.
Electrophysiology of succinate transport across rabbit renal brush border membranes.
Authors: Schell R E , Wright E M
Published: December 2014

In rabbit renal brush border membrane vesicles, the membrane potential was monitored using a voltage‐sensitive optical probe (diS‐C3‐(5)). The ionic dependence of the electrogenic Na+/succinate co‐transporter was determined in the presence of monovalent anions and mono‐, di‐, and trivalent cations. Na+ and La3+ were the only cations capable of supporting a succinate‐dependent membrane depolarization: Li+, K+, Rb+, Cs+, NH4+, Hg2+, Ca2+, Ba2+, Sr2+, Mg2+, Cu2+, Fe2+, Cd2+, Be2+, Pb2+, Zn2+, Mn2+ and Co2+ did not. Succinate increased the Na+ permeability of the brush border membrane in a saturable manner: saturating succinate (3 mM) concentrations increased the Na+/K+ permeability (PNa/PK) ratio from 0.6 to 2.3. In the presence of Na+, Li+ and Hg2+ inhibit the succinate potential: cis‐Li+ inhibition is competitive with an apparent Ki of 2 mM, while trans‐Li+ is noncompetitive; cis‐Hg2+ decreased the maximal depolarization with an inhibitor constant Ki of 8 microM, and this effect was irreversible. Cations having no effect included K+, Rb+, Cs+, NH4+, Ba2+, Ca2+, Mg2+, Sr2+, Cu2+, Fe2+, Cd2+, Co2+, Be2+, Zn2+, Pb2+, Mn2+, and La3+. It is concluded that succinate/Na+ co‐transport produces a specific increase in the Na+ conductance of renal brush borders.
Effects of sodium substitutes on transient inward current and tension in guinea‐pig and ferret papillary muscle.
Authors: Arlock P , Katzung B G
Published: December 2014

We used ouabain‐treated guinea‐pig and ferret papillary muscles to study transient inward current (Iti), after‐contractions, and tonic tension development during voltage‐clamp pulses. Li, sucrose and choline were used isosmotically as Na substitutes to evaluate the effect of altering the Na equilibrium potential. We were unable to detect outward Iti at any potential up to +30 mV in normal or Na‐depleted solutions. However, reduction of Na had a biphasic effect on Iti, initially increasing it and then reducing it at all clamp potentials from ‐50 to +20 mV. After‐contractions were also initially increased and, in sufficiently Na‐depleted solutions, decreased by reduction of extracellular Na. However, the peak in the after‐contraction always occurred later than the increase in Iti and frequently coincided with the maximum suppression of the current. Complete suppression of after‐contractions was not often achieved and always required more complete Na replacement than Iti suppression. Tonic tension responses were reduced by Na replacement, usually in synchrony with the reduction of Iti. The responses of Iti to Na replacement are consistent with a model of electrogenic Na‐Ca exchange over the potential range positive to ‐50 mV. The responses deviate from the predictions of the model at more negative potentials. The results are consistent with the previous proposal that oscillatory changes in internal free Ca concentration underlie both Iti and after‐contractions.
Relation of sodium pump inhibition to positive inotropy at low concentrations of ouabain in rat heart muscle.
Authors: Grupp I , Im W B , Lee C O , Lee S W , Pecker M S , Schwartz A
Published: December 2014

Low concentrations of ouabain which produce a positive inotropic effect on rat ventricular muscle do not inhibit the isolated Na+‐K+‐ATPase enzyme from this tissue, suggesting that these low‐concentration inotropic effects are not related to sodium pump inhibition (Erdmann, Philipp & Scholz, 1980; Adams, Schwartz, Grupp, Grupp, Lee, Wallick, Powell, Twist & Gathiram, 1982). We tested this hypothesis by continuously measuring intracellular Na+ activity with Na+‐selective micro‐electrodes and, separately, twitch tension of rat ventricular muscle during exposure to and wash‐out of ouabain. Intracellular Na+ activity (aiNa) and transmembrane potential of quiescent muscle cells averaged 8.5 +/‐ 2.6 mM (mean +/‐ S.D., n = 27) and ‐79.2 +/‐ 2.4 mV (n = 34) respectively. Low concentrations of ouabain (0.1, 0.5 and 1.0 microM) produced concentration‐dependent increases in both aiNa and twitch tension. At lower concentrations of ouabain (0.01 and 0.05 microM), no detectable changes in aiNa and twitch tension were observed. The data strongly indicate that in rat ventricular muscle sodium pump inhibition is present at low concentrations of ouabain which produce positive inotropy. This is consistent with previous results in canine and sheep cardiac Purkinje fibres.
Effect of fluid pressure on the hydraulic conductance of interstitium and fenestrated endothelium in the rabbit knee.
Authors: Knight A D , Levick J R
Published: December 2014

A synovial cavity is separated from plasma by synovial intima in series with capillary endothelium. Because 20% of the intimal surface is bare interstitium, the system is a convenient model for the study of passive transport through serial endothelial and interstitial layers. Here hydraulic flow across the composite barrier was investigated in forty‐seven knees of isolated, blood‐perfused rabbit hindquarters, at intra‐articular pressures between 4 and 30 cmH2O. In order to measure barrier conductance at constant intra‐articular pressure, pressure on the opposite side of the barrier was varied, i.e. capillary blood pressure (PC). Capillary pressure was changed by alteration of vascular perfusion pressures, and the resulting changes in rate of absorption of Krebs solution from the synovial cavity (QS) were recorded. Trans‐synovial absorption was a negative linear function of PC at each joint pressure, in verification of the applicability of Starling's hypothesis to this system. The hydraulic conductance of the blood‐joint barrier was calculated as dQS/dPC. Conductance was independent of intra‐articular pressure below 9 cmH2O and was 0.12 +/‐ 0.015 microliter min‐1 mmHg‐1 (mean +/‐ S.E. of mean). Barrier conductance increased as a curvilinear function of intra‐articular pressure above 9.4 cmH2O (yield pressure). At 30 cmH2O conductance averaged 0.60 +/‐ 0.06 microliter min‐1 mmHg‐1, a 5‐fold increase. A hyperbolic curve relating net barrier conductance to joint pressure was predicted from the hypothesis that interstitial conductance increases as a monotonic function of intra‐articular pressure above yield pressure (Appendix). The data were in reasonable agreement with the theoretical hyperbola. Interstitial conductivity (3 X 10(‐7)‐7 X 10(‐7) cm4 s‐1 N‐1 below yield pressure) and mean endothelial conductance (1.1 X 10(‐4)‐1.4 X 10(‐4) cm3 s‐1 N‐1) were evaluated and compared with values in other tissues. Synovial endothelium contains on average 0.25 fenestrae micron‐1 circumference. The conductance of a single fenestra was calculated to be 2.3 X 10(‐13) cm5 s‐1 N‐1. Interstitial resistance accounted for roughly half the total resistance below yield point: therefore dQS/dPC should not be equated with 'capillary filtration capacity' in tissues with dense or fenestrated capillary beds. Large inconsistencies between interstitial conductivity and glycosaminoglycan concentration are noted, and mechanistic explanations of increases in conductivity with joint pressure are offered.
The effects of native and modified bovine serum albumin on the permeability of frog mesenteric capillaries.
Authors: Michel C C , Phillips M E , Turner M R
Published: December 2014

Single capillaries in the mesenteries of pithed frogs were perfused sequentially with two frog Ringer solutions. The first solution contained no protein; the second solution contained either native or chemically modified bovine serum albumin (BSA) at a concentration of 3‐5 mg ml‐1. During each perfusion capillary permeability was assessed from the hydraulic conductivity of the capillary wall (Lp) which was determined from measurements of fluid filtration rate at two or more different capillary pressures (Michel, Mason, Curry, Tooke & Hunter, 1974). Lp measured during perfusion with protein‐free Ringer solution was on average three times greater than its value for the same vessel perfused with Ringer solution containing native BSA. This confirms the findings of Mason, Curry & Michel (1977). BSA, which had been succinylated to modify the free amino groups of its lysine residues, appeared to be as effective as native BSA in reducing Lp. After modification of its arginine side chains by exposure to 1,2‐cyclohexanedione (CHD) in the presence of 0.2 M‐NaOH, BSA lost its property of reducing Lp in capillaries perfused with Ringer solution. Exposure of BSA to 0.2 M‐NaOH followed by dialysis against normal Ringer solution did not affect its property of reducing Lp. CHD‐treated BSA at a concentration of 2.5 mg ml‐1 had no effect upon the effective osmotic pressure exerted across capillary walls by Ringer perfusates containing the neutral polymer Ficoll 70 at a concentration of 40 mg ml‐1. Native BSA raised the effective osmotic pressure from 7.07 +/‐ 1.93 cmH2O to 20.50 +/‐ 2.37 cmH2O (n = 7; P less than 0.001). It is concluded that the effects of BSA on permeability depend upon specific sites in the BSA molecule. It is suggested that these sites involve positively charged arginine side chains of the albumin molecule. The results are discussed in terms of the fibre‐matrix hypothesis of capillary permeability and in terms of Brown's (1976) theory for the structure of albumin.
The transneuronal induction of sprouting and synapse formation in intact mouse muscles.
Authors: Rotshenker S , Tal M
Published: December 2014

The pattern of innervation to intact peroneal and extensor digitorum longus muscles of normal and experimental young adult mice was studied by light microscopy after staining neuromuscular junctions by a combined silver‐cholinesterase stain. Spontaneous sprouting and synapse formation occur in intact muscles of normal mice. In about 7% of the junctions, sprouts contribute to the innervation of muscle fibres already innervated by their parent axons. Axotomy of the sciatic nerve in one hind limb is followed by an average 3‐fold increase over normal in the incidence of sprouting and synapse formation in the intact muscles of the opposite hind limb. The time to onset of sprouting and synapse formation becomes shorter as the site of the contralateral axotomy is placed closer to the spinal cord. A significant increase over normal in the incidence of sprouting is first observed 5 days after a proximal sciatic nerve cut and only 12 days after a distal sciatic nerve cut. The timing of sprouting is independent of the difference in the number of axons that are involved in the contralateral axotomies at different sites. These findings suggest that, in the intact muscles of normal mice, sprouting and synapse formation is an ongoing process which can be enhanced by contralateral axotomy. As in frogs (Rotshenker, 1979, 1982) the underlying mechanism may be the transneuronal induction of sprouting and synapse formation.
The secretory action of barium chloride in rat colon.
Authors: Hardcastle J , Hardcastle P T , Noble J M
Published: December 2014

BaCl2, applied serosally, caused a rise in the p.d. and short‐circuit current (s.c.c), and a decrease in tissue resistance in stripped sheets of rat colon. This response was dose dependent. Mucosal application of BaCl2 was without effect. The BaCl2‐induced rise in s.c.c. was inhibited by reducing the serosal Na+ concentration to 25 mM. Lowering the mucosal Na+ concentration was without effect. Ouabain (10(‐3) M in serosal fluid) and furosemide (10(‐3) M in serosal fluid) both reduced the rise in s.c.c. induced by BaCl2. Flux determinations indicated that BaCl2 inhibited Na+ absorption and stimulated Cl‐ secretion by the colon. In vivo, BaCl2 increased fluid accumulation within the colonic lumen, an effect that was associated with a rise in the transcolonic p.d. Increasing the serosal K+ concentration to 20 mM reduced the responses to BaCl2, acetylcholine and theophylline, and this could not be entirely accounted for by the concomitant reduction in the serosal Na+ concentration. As high serosal K+ did not mimic the secretory response it would appear that BaCl2 does not act by blocking K+ channels. The rise in s.c.c. induced by BaCl2 was not reduced by Ca2+‐free conditions, but it was inhibited by 8‐(N,N‐diethylamino)‐octyl‐3,4,5‐trimethoxybenzoate hydrochloride (TMB‐8) and trifluoperazine. BaCl2 did not alter cyclic AMP production by colonic scrapes. It is concluded that BaCl2 induces colonic secretion by the release of intracellular Ca2+, which then combines with calmodulin to activate the secretory process.
Effects of inhibiting carbonic anhydrase on isometric contraction of frog skeletal muscle.
Authors: Scheid P , Siffert W
Published: December 2014

Carbonic anhydrase (CA) activity was determined in a homogenate of frog skeletal muscle by measuring the kinetics of CO2 hydration in a pH stopped‐flow apparatus. The results suggest that frog skeletal muscle contains a high‐activity CA with properties similar to those of the isoenzyme CA II found in white skeletal muscle tissue of the rabbit. In an attempt to assess the functional significance of CA in skeletal muscle, the maximal isometric force of frog gastrocnemius muscle was measured in response to direct or indirect (ischiadic nerve) single‐pulse electrical stimulation before (control) and after exposing the muscle to various concentrations of the specific carbonic anhydrase inhibitors, ethoxzolamide, acetazolamide, and methazolamide. In the range of ethoxzolamide concentration between 10(‐9) and 10(‐6) M, maximal isometric force with indirect supramaximal stimulation declined progressively with inhibitor concentration to less than 10% of the control value. Acetazolamide and methazolamide were less effective in that concentrations of above 10(‐4) M were necessary to inhibit maximum isometric force by 50%. Even at the highest ethoxzolamide concentration used (10(‐6) M), no effect was observed either on the amplitude of the compound nerve action potential or on the conduction velocity of group I fibres in the ischiadic nerve, suggesting that ethoxzolamide did not affect the mechanisms responsible for spike generation or conduction in the motor fibres. With direct supramaximal stimulation of the gastrocnemius muscle, no effects on maximal isometric force were observed of CA inhibition by any of the inhibitors used. The results suggest that CA acts on the neuromuscular transmission. The exact site and mechanism of action are unknown.
Noradrenaline hyperpolarization and depolarization in cat vesical parasympathetic neurones.
Authors: Akasu T , Gallagher J P , Nakamura T , Shinnick-Gallagher P , Yoshimura M
Published: December 2014

Responses to noradrenaline (NA) applied by superfusion, ionophoresis or pressure pulse were analysed using conventional intracellular recording and voltage‐clamp methods in cat vesical parasympathetic ganglia. NA (1 microM) hyperpolarized 60% of the neurones, depolarized 25%, and produced a biphasic potential, which comprised a membrane hyperpolarization followed by a membrane depolarization, in 10%. About 5% of the neurones did not respond to NA. The NA hyperpolarization was blocked by yohimbine (1 microM), an alpha 2‐adrenoceptor antagonist, whereas the NA depolarization was blocked by prazosin (0.1‐1 microM), an alpha 1‐adrenoceptor antagonist. These data indicated that the NA hyperpolarization was mediated through alpha 2‐adrenoceptors and the NA depolarization through alpha 1‐adrenoceptors. The NA hyperpolarization was accompanied by an increase in conductance, while the NA depolarization was associated with a decrease in conductance measured under manual‐clamp conditions. Similar conductance changes were observed under voltage clamp. NA hyperpolarizations became smaller as the membrane was hyperpolarized and reversed polarity beyond ‐100 mV. NA depolarizations also became smaller at hyperpolarized membrane potentials and reversed polarity around ‐90 mV. The NA responses were enhanced in low‐K media and depressed in high‐K Krebs solution. The NA hyperpolarization was blocked by the Ca antagonists, Cd, Mn and Co. Intracellular injection of EGTA caused a slowly developing, progressive block of the NA hyperpolarization. The NA depolarization was not affected by low Ca concentrations, Ca antagonists or intracellular injection of EGTA. In some neurones the NA depolarization was unmasked in solutions containing Ca antagonists and after intracellular EGTA injection. The NA hyperpolarization was depressed by intracellular injection and extracellular superfusion of Cs but not by TEA. Ba (10‐100 microM) depressed the NA hyperpolarization by 30%. The NA depolarization persisted in the presence of muscarine (10 microM) and was not blocked by Cs or TEA but was depressed 70% by Ba (10 microM). These data are consistent with the hypotheses that alpha 2‐adrenoceptor activation produces a membrane hyperpolarization that is mediated through a Ca‐dependent K conductance, and that alpha 1‐adrenoceptor activation produces a membrane depolarization through closure of a voltage‐insensitive K channel.
A nuclear magnetic resonance study of metabolism in the ferret heart during hypoxia and inhibition of glycolysis.
Authors: Allen D G , Morris P G , Orchard C H , Pirolo J S
Published: December 2014

31P nuclear magnetic resonance was used to measure the relative concentrations of phosphorus‐containing metabolites in Langendorff‐perfused ferret hearts. Intracellular concentrations of inorganic phosphate ([Pi]i), phosphocreatine ([PCr]i), ATP ([ATP]i) and H+ (pHi) were monitored under control conditions and while oxidative phosphorylation and/or glycolysis were prevented. Mechanical performance was assessed by recording the pressure developed in a balloon placed in the left ventricle. Oxidative phosphorylation was prevented either by replacement of O2 with N2 or by addition of cyanide. When the rate of oxidative phosphorylation was reduced by either method, developed pressure fell to a stable level of about 35% of control after 5 min. The pHi (control value 6.98) first increased to a peak of 7.07 after 2 min but then decreased to give a stable acidosis (pH 6.85). [PCr]i decreased rapidly to about 15% of the control value after 5 min whereas [ATP]i declined very slowly, reaching about 90% of the control value after 10 min. Reduction in the rate of glycolysis was achieved either (i) by removal of external glucose and depletion of glycogen stores by a long (1‐2 h) period of stimulation or (ii) by removal of glucose and application of 2‐deoxyglucose (1 mM) for 30‐60 min. These procedures had only a small effect on pressure development, [ATP]i, [PCr]i and pHi. Measurements of lactate production showed that these procedures reduced the rate of glycolysis by a factor of about 10. When oxidative phosphorylation was prevented during periods when the rate of glycolysis was reduced, developed pressure fell to less than 5% of control after 5 min and there was a subsequent increase in resting pressure (hypoxic contracture). pHi (control value 7.03) first increased to a peak of 7.12 and then declined to about pH 7.00, but there was no subsequent acidosis. [PCr]i fell rapidly to about 10% of control after about 5 min while [ATP]i declined to about half of its control value over 10 min. It is concluded that (i) when oxidative phosphorylation alone is prevented, the changes in pHi can account for a substantial part of the changes in developed pressure. The increase in [Pi]i probably also contributes to the decline of developed pressure. (ii) When oxidative phosphorylation was prevented under conditions in which the rate of glycolysis was also reduced, the more pronounced decline in developed pressure which occurs within 5 min cannot be accounted for by pHi changes and is probably not explained by the rise in [Pi]i or by the moderate fall of [ATP]i.(ABSTRACT TRUNCATED AT 400 WORDS)
Evidence for two transient sodium currents in the frog node of Ranvier.
Authors: Benoit E , Corbier A , Dubois J M
Published: December 2014

Na current (INa) was monitored in isolated voltage‐clamped frog nodes of Ranvier in order to analyse the pharmacological and kinetic properties of fast and slow phases of inactivation. Niflumic acid (0.1‐10 mM) and tetrodotoxin (0.3‐30 nM) did not alter fast and slow inactivation time courses but preferentially reduced the amplitude of the fast phase of inactivation. The block of both phases of inactivation by niflumic acid and tetrodotoxin was well described if one assumed that more than one molecule of drug reacted with one channel. Fast and slow currents, corresponding respectively to fast and slow phases of inactivation, reversed at different potentials, had different threshold voltages of activation and the slopes of their steady‐state inactivation curves were different. The recovery from inactivation of the compound INa could be described by the sum of two exponentials (plus a delay) corresponding respectively to fast and slow currents. When calculated from INa recorded without and with niflumic acid or tetrodotoxin, the slow current activated about three times more slowly than the fast current. Large prehyperpolarizations delayed both the activation and the inactivation of the fast current but only the activation of the slow current. Lowering the temperature decreased the fast current but increased the slow current. We conclude that the inactivatable Na current of the nodal membrane is made up of two components (INa,f and INa,s) corresponding to two different and interconvertible forms of the Na channel.
Effects of rapid cooling on mechanical and electrical responses in ventricular muscle of guinea‐pig.
Authors: Kurihara S , Sakai T
Published: December 2014

The effect of rapidly lowering bathing solution temperature from 36.5 +/‐ 0.5 degrees C to various low temperatures was examined in guinea‐pig ventricular muscle to explore the possible role of intracellular Ca2+ store sites in excitation‐contraction coupling. Rapid cooling from 36.5 +/‐ 0.5 degrees C to below 18 degrees C caused contracture (rapid cooling contracture, r.c.c.) with subthreshold depolarization for contraction, if electrical stimulation was applied before cooling. R.c.c. peak tension depended on cooling temperature, and pre‐cooling stimulation frequency and duration. R.c.c. induced after pre‐cooling stimulation was enhanced by increased extracellular Ca2+ ( [Ca2+]o) and decreased by reduction of [Ca2+]o. Co2+ (2‐4 mM) added to the HEPES‐buffered Krebs solution, which suppressed the action potential plateau and inhibited twitch response, did not abolish r.c.c. after pre‐cooling stimulation at high frequency. Reduction of extracellular Na+ concentration ( [Na+]o) before cooling enhanced r.c.c., and even in non‐stimulated preparations, incubation in low [Na+]o below 68.8 mM for 20 min produced r.c.c. R.c.c. was superimposed on the tonic component of the K+ contracture, after a quiescent preparation has been depolarized beyond ‐40 mV by addition of solid KCl to normal Krebs solution. The relation between r.c.c. tension and membrane potential was shifted to the left along the voltage axis by reducing [Na+]o and shifted to the right by decreasing [Ca2+]o. Results suggest that well‐developed intracellular Ca2+ store sites could sequester enough Ca2+ to generate tension by an energy‐dependent process which had been loaded mainly by a voltage‐dependent Na+‐Ca2+ exchange mechanism and Ca2+ current, and that rapid cooling could cause Ca2+ release from the intracellular store sites with little contribution to membrane excitation in the guinea‐pig ventricular muscle.
Myoelectrical activity and propulsion in the large intestine of fed and fasted rats.
Authors: Ferré J P , Ruckebusch Y
Published: December 2014

Electrical spiking activity of different parts of the colonic wall was studied in relation to the mechanical events in conscious rats fitted with chronically implanted nichrome wire electrodes and miniaturized strain‐gauge transducers. The progress of barium sulphate introduced into the caecum and measured radiographically at fixed intervals was used as an index of transit rate of colonic contents in both the fasted and fed state. The basic pattern of colonic myoelectrical activity was characterized by randomly occurring spike bursts at a higher frequency in the proximal (0.9/min) than the distal colon (0.5/min). Their duration in the fasted state, which was shorter in the proximal (5.5 +/‐ 1.7 s) than the distal colon (12.7 +/‐ 2.9 s), was similar following a meal. In the fasted state, integrated records showed cyclical periods of more intense electrical activity lasting about 20 and 40 min in the proximal and the distal colon, respectively. The cyclical pattern following a meal occurred at shorter intervals in the different parts of the colon. Conversely, the propulsion of the marker over the whole colon, which lasted 180‐200 min, was accelerated by 30% after feeding. Laxatives disrupted these cyclical motor events on the colon, by inducing mass movements which impeded the pellet formation and increased the rate of transit. The cyclical motor activity was also disrupted following the administration of opiate agonists, the rate of transit being decreased and propulsive activity inhibited. The results are consistent with the concept of cyclical motor pattern playing an important part in the control of pellet formation and movement of digestive contents within the colon of the rat.
Influence of human muscle length on fatigue.
Authors: Fitch S , McComas A
Published: December 2014

The effect of muscle length on susceptibility to fatigue has been examined in human ankle dorsiflexor muscles. The fatiguing procedure consisted of either indirect tetanic stimulation at 20 Hz or maximal voluntary contraction; each procedure lasted 90 s. The amplitude of the evoked muscle compound action potential (M‐wave) increased during the first 30 s or so of the tetanic fatiguing procedure and then decreased. The torque developed by the dorsiflexor muscles declined throughout the period of tetanization. A significantly greater reduction in twitch and tetanic torque was found after the fatiguing procedure had been conducted at the optimum muscle length rather than with the muscle in a shortened position. Relaxation after tetanic stimulation was slower after fatigue had been induced at the optimum muscle length. It is concluded that muscle fatigue is related to the number of actin‐myosin cross‐bridge interactions and is unlikely to be accounted for solely on the basis of changes in the ionic composition of the transverse tubular fluid.
Substance P provoked gamma‐aminobutyric acid release from the myenteric plexus of the guinea‐pig small intestine.
Authors: Tanaka C , Taniyama K
Published: December 2014

The release of [3H]gamma‐aminobutyric acid (GABA) from the isolated small intestine of the guinea‐pig pre‐loaded with [3H]GABA was measured in the presence of substance P and vasoactive intestinal polypeptide (VIP). Substance P (10(‐10)‐10(‐7) M) produced a dose‐dependent increase in the fractional rate of [3H]GABA release. VIP, even at 10(‐7) M, did not affect the spontaneous [3H]GABA release nor the release of [3H]GABA evoked by electrical transmural stimulation (0.5 ms, 15 V, 10 Hz for 30 s). The release of endogenous GABA from the isolated small intestine was measured in the presence of substance P (10(‐9) M). After 60 min superfusion, the spontaneous release of GABA was 4.61 +/‐ 0.14 pmol min‐1 g‐1 wet wt. (n = 20). Substance P (10(‐9) M) produced an approximate 2‐fold spontaneous release of endogeneous GABA (8.74 +/‐ 0.21 pmol min‐1 g‐1 wet wt. (n = 10)). Perfusion with Ca‐free medium containing 1 mM‐EGTA and tetrodotoxin (3 X 10(‐7) M) inhibited the release of endogenous GABA evoked by substance P (10(‐9) M). (D‐Pro2, D‐Trp7,9) substance P (10(‐6) M) antagonized the release of endogenous GABA evoked by substance P (10(‐9) M). These results indicate that substance P induces a neuronal release of GABA through its receptor located in the guinea‐pig small intestine. Substance P (10(‐11)‐10(‐7) M) produced a dose‐dependent increase in the fractional rate of [3H]acetylcholine (ACh) release from the isolated small intestine pre‐loaded with [3H]choline. The release of [3H]ACh evoked by substance P (10(‐9) M) was inhibited by perfusion with Ca‐free medium containing 1 mM‐EGTA, tetrodotoxin (3 X 10(‐7) M) and (D‐Pro2, D‐Trp7,9)substance P (10(‐6) M). Bicuculline (10(‐6) M) inhibited the release of [3H]ACh evoked by substance P (10(‐9) M) by 68.1 +/‐ 4.6% (n = 5), thereby suggesting that the substance P‐evoked ACh release is partly mediated through the endogenous GABA released by substance P. These results provide evidence for the neurotransmitter role of GABA and a possible excitatory role of substance P on the GABAergic neurones in the myenteric plexus of the guinea‐pig small intestine.
Dual‐component amino‐acid‐mediated synaptic potentials: excitatory drive for swimming in Xenopus embryos.
Authors: Dale N , Roberts A
Published: December 2014

The neuronal basis of the excitation received by motoneurones during swimming in curarized Xenopus embryos has been investigated further. Extracellular stimulation of axons in the fibre tracts of the spinal cord has been used to evoke unitary excitatory post‐synaptic potentials (p.s.p.s) in motoneurones. The p.s.p.s. had a rise time of 3‐5 ms and a long falling phase lasting up to 200 ms. These potentials consist of two components: a 'fast' p.s.p. which is insensitive to 50 microM‐(+/‐)‐2‐amino‐5‐phosphonovaleric acid (APV) but is blocked by 2 mM‐cis‐2,3‐piperidine dicarboxylic acid (PDA) and is therefore probably mediated by kainate/quisqualate receptors, and a 'slow' p.s.p. which is blocked by both APV and PDA and is therefore probably mediated by N‐methyl‐D‐aspartate (NMDA) receptors. Paired intracellular recordings from motoneurones and interneurones have revealed a class of spinal cord interneurone which makes descending excitatory amino‐acid‐dependent synapses onto motoneurones and commissural interneurones. The p.s.p.s evoked by intracellular stimulation of these excitatory interneurones consist of 'fast' and 'slow' components identical in shape and pharmacological properties to those of the extracellularly evoked potentials. One neurone may, therefore, be able to release a transmitter which activates both NMDA and non‐NMDA receptors on the same post‐synaptic neurone generating fast and slow post‐synaptic potentials. The excitatory interneurones play an important role in the generation of the swimming pattern in the curarized Xenopus embryo. Like motoneurones, they fire once per swimming cycle in phase with the ipsilateral motoneurones and receive a background excitation during swimming that is excitatory amino acid mediated. They are therefore part of the swimming rhythm generator. The temporal summation of the extracellularly evoked p.s.p.s shows that these excitatory interneurones are sufficient to generate the excitatory drive received by motoneurones during swimming.
Renal extraction and clearance of p‐aminohippurate during saline and dextrose infusion in the rat.
Authors: Lote C J , McVicar A J , Yardley C P
Published: December 2014

The reliability of the use of p‐aminohippurate (PAH) as a clearance marker for the determination of renal plasma flow during saline or dextrose infusion was investigated in conscious and anaesthetized rats. In the conscious rat (wt. 350‐400 g) infused for 4 h with 0.85% saline followed by 3 h of 2.5% dextrose, PAH clearance averaged 11.50 +/‐ 1.45 ml/min during saline infusion and 7.83 +/‐ 0.82 ml/min during dextrose infusion. The difference was significant (P less than 0.02). Inulin clearance, however, was unchanged. With dextrose as the initial infusate, PAH clearance averaged 5.86 +/‐ 0.65 ml/min and increased (P less than 0.01) to 8.74 +/‐ 0.71 ml/min following a change of infusate to saline, although inulin clearance was again unchanged. In separate groups of rats anaesthetized with sodium pentobarbitone, a comparison was made between renal blood flow values calculated from PAH clearance and haematocrit, and those determined simultaneously using an electromagnetic flow probe placed on the left renal artery. During 0.85% saline infusion, the calculated value was 88.1 +/‐ 8.4% of that measured using the flow probe. During 2.5% dextrose infusion the value determined from PAH clearance was only 47.3 +/‐ 4.2% of that obtained using the flow probe, and this is significantly (P less than 0.01) lower than the ratio found during saline infusion. In another study, renal venous blood samples were obtained from sodium‐pentobarbitone‐anaesthetized rats during 0.85% saline or 2.5% dextrose infusions, for calculation of the renal PAH extraction ratio. During saline infusion, PAH extraction averaged 68.3 +/‐ 2.5%, whereas during dextrose infusion PAH extraction was lower (P less than 0.001) and averaged only 48.8 +/‐ 3.2%. It is concluded that PAH clearance grossly underestimates renal plasma flow during 2.5% dextrose infusion in the rat.
Development of synaptic currents in immobilized muscle of Xenopus laevis.
Authors: Kullberg R , Owens J L , Vickers J
Published: December 2014

The effect of chronic immobilization on the development of synaptic currents was studied in myotomal muscle of Xenopus laevis. Embryos and tadpoles were immobilized by rearing them in the presence of tetrodotoxin (TTX) after removal of the egg membranes. Immobilization did not affect the developmental change in duration of miniature end‐plate currents (m.e.p.c.s). Rise times decreased from about 3 to 0.6 ms in both immobilized and control muscle, and decay constants decreased from about 7 to 1 ‐ 2 ms in both conditions. M.e.p.c.s with double exponential decays were recorded in both immobilized and control muscle at intermediate and late developmental stages. The fast and slow decay constants were 0.7 ms and slightly less than 3 ms in older muscle of both groups. These values are comparable to the apparent open times of fast and slow ACh receptors present on Xenopus muscle. Application of an anticholinesterase (methanesulphonyl fluoride) lengthened the duration of m.e.p.c.s comparably in immobilized and control muscle. These data indicate that the deposition of junctional acetylcholinesterase and the reduction in open time of acetylcholine receptor channels in developing Xenopus myotomal muscle are independent of contractile activity of muscle and TTX‐blockable action potentials in muscle or motoneurones.
A calcium‐activated chloride current generates the after‐depolarization of rat sensory neurones in culture.
Authors: Mayer M L
Published: December 2014

Neurones from the dorsal root ganglia of 1‐day‐old rat pups were grown in dissociated culture and voltage clamped using patch electrodes for whole‐cell recording. The pipettes were filled with either 140 mM‐KCl or CsCl. Depolarizing voltage jumps activated net inward calcium currents in all neurones, which in a subpopulation of 46% were followed by slowly decaying inward tail currents accompanied by large increases in membrane conductance. During voltage jumps to membrane potentials more positive than 0 mV the inward calcium current was contaminated by a slow outward relaxation only in those neurones with slow inward tail currents. The availability curve for the slow inward tail current was U shaped, with a peak at approximately +5 mV in medium containing 2.5 mM‐Ca2+; further depolarization reduced the amplitude of the tail current. During perfusion with calcium‐free solution, or in the presence of the calcium‐channel blockers cadmium or cobalt, or on substitution of barium for calcium, both the slow inward tail currents and outward relaxations were reversibly blocked. The reversal potential of the slow inward tail current, measured using a twin‐pulse protocol, was approximately ‐10 mV. Replacement of sodium by tetraethylammonium (TEA) did not reduce the slow inward tail current, nor change its reversal potential. Reduction of the extracellular chloride activity produced a large increase in the amplitude of the slow inward tail current suggesting an increase in permeability to anions. This conductance, which behaves as though activated by prior or concurrent calcium entry triggered by membrane potential depolarization, is referred to as ICl(Ca). The activation and deactivation kinetics of ICl(Ca) are complex: envelope experiments measuring peak tail current amplitude revealed activation to be described by a single exponential function, of time constant approximately 100 ms at ‐10 to +8 mV. The integral of the tail currents increased with the duration of depolarizing pre‐pulses suggesting accumulation of intracellular calcium. The decay of tail currents activated by short depolarizing voltage jumps was described by a single exponential function of time constant approximately 200 ms at ‐60 mV; more complex decay kinetics were recorded following activation by voltage jumps of duration greater than 60 ms. Tail current decay was voltage sensitive, becoming faster with hyperpolarization and increasing e‐fold per 120 mV change in membrane potential.