bluuebunny/crossref_metadata_2025 huggingface dataset:
The elasticity of relaxed insect fibrillar flight muscle.
Authors: White D C
Published: December 2014

The mechanical properties of glycerol‐extracted fibres from the dorsal longitudinal muscle of Lethocerus have been determined by sinusoidal and transient analysis in the time range 1 ms‐1000 s, and from rest length to 10% strain for fibres in relaxing and rigor solutions. The fibres behave reversibly up to strains of about 5%, but reach an elastic limit in the range 5‐9% strain, depending upon the rate of strain. Electron micrographs of fibres at different degrees of stretch, and after partial extraction of the contractile proteins, suggest that a connexion between the end of the A filament and the Z line, named a C filament, is responsible for the high stiffness of the relaxed muscle. Estimates are made of the compliance of the A, I and C filaments. The mechanical response of the relaxed muscle, over the entire frequency range studied, is assignable to the C filaments. An analysis of the stiffness of the fibres at different tensions in activating and relaxing solutions, and in fibres relaxed by orthovanadate, shows that the C filaments still exert their mechanical effect in the active muscle. That is, the response of the active muscle consists of the contribution from the cross‐bridges plus that of the C filaments, acting mechanically in parallel. This situation is incompatible with earlier explanations of the fully activated mechanical dynamics of fibrillar muscle. Alternative explanations at the cross‐bridge level are described in the paper that follows this one.
Sodium metabolism in rat resistance vessels.
Authors: Aalkjaer C , Mulvany M J
Published: December 2014

Using 22Na we have investigated the Na metabolism in rat mesenteric resistance vessels (internal diameter about 200 micron). The intracellular Na content was determined by washing the vessels at 0 degrees C in saline with Li substituted for Na, and was related to smooth muscle volume determined from measurements of media thickness and internal diameter using light microscopy. On this basis an internal Na concentration of 13.7 mmol l‐1 cells was found. The efflux of Na into saline at 37 degrees C consists of two phases, a fast one and a slow one, where the slow phase was considered to be intracellular. It had a rate constant of 0.137 min‐1, which was decreased by 50% if 1 mM‐ouabain was added to or K withdrawn from the efflux medium. The gain of cell Na after addition of 1 mM‐ouabain was much faster than would be expected from the decrease in efflux, indicating that 1 mM‐ouabain increases the permeability to Na.
Perchlorate‐induced alterations in electrical and mechanical parameters of frog skeletal muscle fibres.
Authors: Gomolla M , Gottschalk G , Lüttgau H C
Published: December 2014

The effect of the perchlorate anion (ClO4‐) on the potential dependence of mechanical and electrical parameters was investigated in skeletal muscles fibres of the frog. Two main methods were employed: twitches and K contractures were induced in isolated fibres from the semitendinosus or iliofibularis muscle, and point voltage clamp was applied in sartorius and short toe muscle fibres. Twitch height was unaffected below 10(‐4) M‐ClO4‐, it usually increased several‐fold in the concentration range of 10(‐3) to 10(‐2) M‐ClO4‐ and continued to rise slowly between 10(‐2) and 10(‐1) M‐ClO4‐. ClO4‐ caused a parallel shift of the activation curve, which relates peak force to membrane potential, towards more negative potentials by up to 40 mV (70 mM‐ClO4‐). The shift in force activation was not accompanied by a corresponding shift in the potential dependence of force inactivation. In the presence of ClO4‐, maximum force development upon depolarization to ‐60 or ‐50 mV could be maintained for several minutes, suggesting that spontaneous relaxation after full depolarization is due to a potential‐dependent inactivation process, and not to an exhaustion of Ca2+ release. ClO4‐ shifted the threshold for the initiation of the action potential only slightly towards more negative potentials (approximately 10 mV at 70 mM‐ClO4‐). Little or no shift was observed in the lower concentration range (less than 10 mM) where the threshold of force activation was shifted by about 20 mV. ClO4‐ slightly depressed the activation of the delayed rectifier without causing any distinct change in its threshold potential. Electrophoretic injection of ClO4‐ (internal ClO4‐ concentration ([ClO4‐]i) approximately 1 mM) induced similar effects to those following external application of this anion, i.e. a shift of force activation towards more negative potentials. Of several other anions tested, only dichromate, which resembles ClO4‐in its tetrahedal structure, similarly caused force activation after repolarization. We conclude that at low concentrations (less than 10 mM) ClO4‐ rather specifically improves excitation‐contraction coupling by direct interference with the gating mechanism which activates Ca release from the sarcoplasmic reticulum. At higher concentrations, it may also influence potential‐dependent membrane processes by adsorption to the outer surface of the membrane.
Mechanisms of the nitroglycerine‐induced vasodilation in vascular smooth muscles of the rabbit and pig.
Authors: Itoh T , Kuriyama H , Ueno H
Published: December 2014

The effects of nitroglycerine (NG) on the mechanical responses of small pieces of intact and skinned smooth muscles of the mesenteric artery, were investigated, as were the Ca fluxes of isolated smooth muscle cells of the coronary artery. NG (10(‐6)‐10(‐5) M) inhibited both phasic and tonic components of the K‐induced contraction; however, the tonic component was more sensitive to NG. The minimum concentration of NG required to decrease significantly the tonic response evoked by 39 mM‐external K was 10(‐8) M. NG (10(‐5) M) reduced the number of oscillatory contractions evoked by 10(‐5) M‐noradrenaline (NAd). After complete removal of stored Ca, the addition of Ca did not produce contraction in polarized muscle (5.9 mM‐external K), yet depolarized muscles (128 mM‐external K) did contract. Addition of NG (10(‐5) M) with Ca produced no change in the resting tone in polarized muscles but inhibited the contraction in depolarized muscles. After application of NG (10(‐5) M), caffeine or NAd consistently produced smaller contraction in both polarized and depolarized muscles in Ca‐free solution. NG (10(‐5) M) inhibited the Na‐free contraction evoked by prolonged treatment with Na‐free solution. Contractions evoked by repetitive applications of 10(‐5) M‐NAd or 10 mM‐caffeine persisted longer in Na‐free, Ca‐free (EGTA) solution than those observed in Ca‐free Krebs solution, but when NG was added to the Na‐free, Ca‐free (EGTA) solution, the contractions ceased more rapidly than in the absence of NG. In chemically skinned muscles, 10(‐5) M‐NG had no effect on the pCa‐tension relationship. The absolute amplitude of Ca‐induced contraction was also not affected by 10(‐5) M‐NG. In these muscles, when the amount of stored Ca was estimated from the amplitude of the caffeine‐induced contraction, Ca accumulation into and release from store sites were unaffected by 10(‐5) M‐NG. The effects of 10(‐5) M‐NG on the accumulation and efflux of 45Ca in isolated cell suspensions prepared from the porcine coronary artery were investigated. The amount of 45Ca taken up by cells after 1‐30 min incubation in 45Ca‐containing solution, and the 45Ca efflux in Ca‐free (EGTA) solution, were not affected by 10(‐5) M‐NG. In the presence of 3 X 10(‐6) M‐acetylcholine (ACh), the efflux of 45Ca into Ca‐free (EGTA) solution was accelerated and with the addition of 10(‐5) M‐NG plus 3 X 10(‐6) M‐ACh, this efflux was even further enhanced.(ABSTRACT TRUNCATED AT 400 WORDS)
Ionic movements through light‐sensitive channels of toad rods.
Authors: Capovilla M , Caretta A , Cervetto L , Torre V
Published: December 2014

Electrical photoresponses of rods in the isolated toad retina were recorded during ionic manipulations of the Na+‐free extracellular medium. In the presence of a concentration of external Ca2+ above 10(‐5) M, voltage photoresponses were observed only in the presence of external Na+ or Li+. When external Ca2+ was reduced below 10(‐6) M, voltage photoresponses of normal polarity could be detected even in the absence of Na+ or Li+, but in the presence of external Mg2+. In the presence of normal extracellular Ca2+ hyperpolarizing photoresponses were observed even in the absence of Na+ or Li+, provided small amounts of phosphodiesterase inhibitors (IBMX, RO 20‐1724, papaverine, caffeine, theophylline) were added to the perfusate. Responses obtained in low‐Na+ IBMX solutions required the presence of millimolar amounts of a variety of divalent cations, among which Mn2+ and Ba2+ were the most effective. When the concentration of both external Ca2+ and Mg2+ was reduced to micromolar amounts, depolarizing photoresponses were observed. In these conditions measurements with radioactive tracers showed a light‐modulated efflux of 42K+ or 86Rb+. The light‐modulated 42K+ or 86Rb+ efflux was halved by 2 X 6 mM‐external K+ and was completely blocked when K+ was raised above 10 mM. These results show that ionic movements through light‐sensitive channels are controlled by Ca2+ and Mg2+ and possibly also be the intracellular level of cyclic nucleotides. Moreover, the movement of ions through the light‐sensitive channel, does not obey the independence principle.
The mechanics of walking in children.
Authors: Cavagna G A , Franzetti P , Fuchimoto T
Published: December 2014

The work done at each step, during level walking at a constant average speed, to lift the centre of mass of the body, to accelerate it forward, and to increase the sum of both gravitational potential and kinetic energies, has been measured at various speeds on children of 2‐12 years of age, with the same technique used previously for adults (Cavagna, 1975; Cavagna, Thys & Zamboni, 1976). The pendulum‐like transfer between potential and kinetic energies (Cavagna et al. 1976) reaches a maximum at the speed at which the weight‐specific work to move the centre of mass a given distance is at a minimum ('optimal’ speed). This speed is about 2 X 8 km/hr at 2 years of age and increases progressively with age up to 5 km/hr at 12 years of age and in adults. The speed freely chosen during steady walking at the different ages is similar to this ‘optimal’ speed. At the ‘optimal’ speed, the time of single contact (time of swing) is in good agreement with that predicted, for the same stature, by a ballistic walking model assuming a minimum of muscular work (Mochon & McMahon, 1980). Above the ‘optimal’ speed, the recovery of mechanical energy through the potential‐kinetic energy transfer decreases. This decrease is greater the younger the subject. A reduction of this recovery implies a greater amount of work to be supplied by muscles: at 4 X 5 km/hr the weight‐specific muscular power necessary to move the centre of mass is 2 X 3 times greater in a 2‐year‐old child than in an adult.
Possible role of calmodulin in renin secretion from isolated rat kidneys and renal cells: studies with trifluoperazine.
Authors: Fray J C , Lush D J , Share D S , Valentine A N
Published: December 2014

Trifluoperazine, an inhibitor of calmodulin and calmodulin‐directed secretion, was used to examine a possible role of calmodulin in renin secretion from isolated perfused kidneys and renal cortical cells. In isolated perfused kidneys trifluoperazine stimulated basal renin secretion in a dose‐dependent manner, with 10 microM causing no stimulation and 50 microM causing 167% increase. Trifluoperazine potentiated the elevated renin secretion induced by isoprenaline and low Ca in isolated kidneys. In renal cortical cells trifluoperazine increased basal renin secretion and potentiated the secretion induced by Ca omission. Cells homogenized immediately after 1 h exposure to trifluoperazine had a substantial reduction in soluble renin without any effect on the change in granular renin. In the absence of trifluoperazine, soluble renin increased with O Ca and decreased with 1.5 mM‐Ca. It is concluded that trifluoperazine stimulates renin secretion by a cellular mechanism possibly at the level of the juxtaglomerular cell. It is suggested that the role of trifluoperazine, and by inference calmodulin, in the secretion of renin may be quite different from its role in secretion of several other substances.
Endocrine responses to exogenous bombesin and gastrin releasing peptide in conscious calves.
Authors: Bloom S R , Edwards A V , Ghatei M A
Published: December 2014

The effects of I.V. infusions of synthetic amphibian bombesin and porcine gastrin releasing peptide (GRP), at a dose of 5 pmol/kg. min for 30 min, have been investigated in conscious calves 3‐6 weeks after birth. The protocols produced a closely similar rise in the bombesin‐like immuno‐reactivity of the arterial plasma of 208 +/‐ 14 pmol/l (bombesin) and 210 +/‐ 32 pmol/l (GRP) which fell exponentially with a half‐life of about 3 min when the infusions were terminated. Neither peptide produced a discernible change in mean heart rate or aortic blood pressure, or in the mean arterial plasma concentrations of enteroglucagon, gastric inhibitory peptide (GIP), gastrin or cholecystokinin (CCK). GRP, but not bombesin, produced a small but significant rise in the mean plasma somatostatin concentration. Both peptides produced a significant rise in mean plasma pancreatic glucagon and pancreatic polypeptide concentration and proved to be exceptionally potent insulinotropic agents. These responses were associated with a rise in plasma glucose concentration which could not be attributed to a direct action of GRP on the liver. The distribution of bombesin‐like immunoreactivity in the gastrointestinal tract was consistent with the findings of other workers who have concluded that it is restricted to nerve terminals. However, our other findings show that GRP is capable of acting as a true hormone.
Accurate regeneration of an electrical synapse between two leech neurones after destruction of the ensheathing glial cell.
Authors: Elliott E J , Muller K J
Published: December 2014

An interneurone, the S cell in the central nervous system of the leech, regenerates its severed axon and forms an electrical synapse with its target, another S cell, entirely within the ensheathment of two glial cells. After the two glial cells were killed selectively by intracellular injection of protease, axonal regeneration and synapse formation occurred in a normal fashion during the month following nerve injury. Soon after reconnexion of S cells, the conduction of impulses across the non‐rectifying electrical junction between the cells was more reliable from the target than into it from the thinner regenerating axon. The distal segments of severed S‐cell axons survived for weeks or months after destruction of their glial cells, indicating that the ensheathing glia is not required for long‐term survival of axon segments. The distal axon segment of the S cell remained connected to the target axon at the normal region of synapse midway between ganglia within the nerve cord. In about half the cases in which reconnexion between injured S cell and target S cell occurred between 10 and 25 days following nerve crush, the regenerating neurone had formed an electrical synapse with its severed distal axon and had thereby become reconnected, indirectly, with its target. In the other cases, reconnexion was by direct contact. By 4 weeks, the proportion of injured S cells that were coupled and making direct contact with their targets rose to more than 80% of the total population, indicating that regeneration continued until the two S cells contacted one another directly. This is similar to the course of S‐cell regeneration in the presence of the ensheathing glia. Microscopy of the regenerating neurone and both its distal axon segment and its target showed that the site of synapse formation in the absence of the usual glial sheath was normal. Fluorescence microscopy following intracellular injection of Lucifer Yellow dye, which crosses between S cells at the electrical synapse, showed that the regenerated synapse formed specifically between S cells. Moreover, the target did not form alternative synapses when regeneration failed.
Response of the normal human ankle joint to imposed sinusoidal movements.
Authors: Evans C M , Fellows S J , Rack P M , Ross H F , Walters D K
Published: December 2014

Ankle joints were subjected to sinusoidal movements at a range of amplitudes and frequencies. Records were made of electromyograms (e.m.g.s) in calf muscles, and of the forces at the joints. When the leg is relaxed, the ankle joint resists an imposed sinusoidal movement with a small approximately sinusoidal force. It is stiffer in its resistance to small movements than to large ones, and this resistance is greater when the joint is dorsiflexed than when it is plantarflexed. If the subject exerts a steady mean flexing force, the imposed sinusoidal movement generates reflex activity which may be recorded as a modulation of the gastrocnemius and soleus e.m.g.s. The e.m.g. response to the sinusoidal movement occurs later in cycles of movement at high than at low frequencies, as one could expect of a reflex pathway that involves a delay. The results suggest that this delay is between 50 and 60 ms, and we conclude that under these circumstances spinal stretch reflexes are playing the important part. The relation of the resisting force to the movement has been displayed as a vector. As the frequency changes, this vector describes the circular path that is characteristic of a system which includes delays or lags; this path enables one to draw conclusions about the amplitude and timing of the reflex resistance to the movement. When a subject exerts a moderate flexing force against the sinusoidal movement for some minutes, the reflex response becomes progressively potentiated. A subject whose reflex responses are normally slight may then exhibit a vigorous reflex response to the movement of that ankle. This enhancement of spinal reflex activity was accompanied by an increase in the myotatic reflex response at the ankle. Reflex responses to sinusoidal movement were most clearly seen when the subject exerted a mean flexing force that amounted to about one‐fifth of his maximum. Very small movements (+/‐ 0.5 degrees) generated little or no reflex response. With large amplitudes of movement there was more reflex activity, but at some amplitude (which varied from subject to subject and from time to time) the reflex mechanism appeared to ‘saturate', and further increases in amplitude were not accompanied by comparable increases in the reflex response. With movements at 10‐15 Hz the e.m.g. response often became large in alternate cycles, with less activity in the intervening cycles.(ABSTRACT TRUNCATED AT 400 WORDS)
Comparison of membrane electrical activity of cat gastric submucosal arterioles and venules.
Authors: Morgan K G
Published: December 2014

Intracellular electrical recordings were made from arterioles and venules of the cat gastric submucosa. Spontaneous rhythmic fluctuations of the membrane potential were recorded in 54% of the venular preparations. Arteriolar cells showed no spontaneous activity. Excitatory junction potentials were recorded in arterioles but not venules after single shocks to the perivascular nerves. The amplitude of the excitatory junction potential was decreased in the presence of alpha‐blockers. Repetitive stimulation of the perivascular nerve caused a biphasic electrical response of venular smooth muscle cells. The depolarizing component was decreased by alpha‐adrenergic blockade and the hyperpolarizing component by beta‐blockade. Venules contracted in response to smaller depolarizations than did arterioles. The voltage threshold for contraction of venular cells was similar to that for arteriolar cells but the venular cells were significantly more depolarized at rest than were the arteriolar cells. The difference in resting potential provides an explanation for the difference in sensitivity to electrical input.
The effect of circulatory occlusion on the glycogen phosphorylase‐synthetase system in human skeletal muscle.
Authors: Chasiotis D , Hultman E
Published: December 2014

The effect of circulatory occlusion upon the glycogen phosphorylase‐synthetase system in intact human muscle at rest has been investigated using the needle biopsy technique. The fraction of phosphorylase in the a form was 26% before occlusion and decreased to 9% after 40 min of occlusion. Synthetase I activity was unchanged during occlusion. After 40 min of occlusion the content of phosphocreatine was decreased by 40%, with a corresponding increase in creatine and inorganic phosphate (Pi). The observed glycogenolytic rate increased during occlusion up to 0.8 mmol glycosyl units kg‐1 dry muscle min‐1. An intracellular Pi concentration at rest of 2.0 mmol l‐1 was calculated from the activities of phosphorylase a and synthetase I assuming that under these conditions they are equal. It is concluded that the glycogenolytic rate during occlusion is a function of both the fraction of phosphorylase in the a form and the availability of Pi at the active site of the enzyme.
Ionic currents of solitary horizontal cells isolated from goldfish retina.
Authors: Tachibana M
Published: December 2014

Solitary horizontal cells, dissociated from papain‐treated goldfish retinas, produce action potentials and show a non‐linear current‐voltage relationship. Underlying ion‐conductance mechanisms were analysed by a single‐micro‐electrode voltage‐clamp technique. Pharmacological and ion‐substitution experiments revealed that ionic currents could be separated into at least four voltage‐dependent currents: a Ca current and three types of K currents. The Ca current was activated by membrane depolarization beyond ‐45 mV, reached a maximal value near 0 mV, and became smaller at more positive potentials. By extrapolation, the reversal potential was estimated to be approximately +50 mV. The Ca current was inactivated by accumulation of intracellular Ca ions but not by membrane depolarization. Co ions (4mM) blocked this current. The first type of K current showed anomalous (inward‐going) rectification near the resting potential (congruent to ‐60 mV). Hyperpolarization from the resting level produced a large, almost steady inward current, while depolarization evoked only a small, steady outward current. The current‐voltage relationship revealed a shallow negative resistance region at membrane potentials beyond ‐50 mV. The current was blocked by Cs (10 mM) or Ba (1 mM) ions. The second type of K current (the transient outward current) was activated by membrane depolarization beyond ‐25 mV. The peak amplitude increased almost exponentially as the membrane was depolarized. During steady depolarization this current decayed exponentially (time constant congruent to 500 ms at +20 mV). The current was inactivated by conditioning depolarization (greater than 10 s) beyond ‐30 mV and blocked by 4‐aminopyridine (10 mM). The third type of K current was the maintained outward current which was activated by membrane depolarization beyond ‐20 mV, increased to a steady level in a few hundred milliseconds, and showed little inactivation. The amplitude increased as the membrane was depolarized. The current was blocked by tetraethylammonium ions (20 mM). A Ca‐mediated K current was not detected. Action potentials and the non‐linear current‐voltage relationship of solitary horizontal cells can be explained qualitatively by the combination of the four ionic currents.
Binding of sodium and potassium to the sodium pump of pig kidney evaluated from nucleotide‐binding behaviour.
Authors: Jensen J , Nørby J G , Ottolenghi P
Published: December 2014

Using a rate‐dialysis technique at 0‐2 degrees C, the affinities of Na+ and K+ for the sodium pump of pig kidney outer medulla were determined from their effects on the binding of ADP to the enzyme. Since all experiments were carried out in the presence of Tris, the enzyme in absence of its specific ligands was assumed to be in a 'sodium‐like' conformation. The model used in the analysis of the results assumed the enzyme to be a dimeric structure with two identical high‐affinity nucleotide‐binding sites. It is concluded from the data that the effects of Na+ and K+ on the binding of nucleotide to either subunit of a nucleotide‐free enzyme are identical. The two subunits, taken together, have five identical and non‐interacting K+‐binding sites (Kdiss = 0.5 mM) whose occupation antagonizes nucleotide binding. The binding of a nucleotide molecule to a nucleotide‐free enzyme results in the abolition of K+ binding to two of the five K+‐binding sites. The binding of the second molecule of nucleotide prevents the binding of three more K+ ions to the enzyme. These results can explain the K+‐induced curvature observed in nucleotide‐binding isotherms in Scatchard plots. The two subunits, taken together, have five identical and non‐interacting Na+‐binding sites (Kdiss = 0.5 mM) whose occupation antagonizes the effects of K+ on nucleotide binding, but does not affect nucleotide binding directly. A few experiments carried out at 18 degrees C indicate that the model applies also at this temperature. It is likely that the cation sites investigated are intracellular ones and it is concluded that the binding of each cation to its site induces a specific conformational change in the neighbourhood of the site itself without affecting the regions around the remaining cation binding sites.
Divalent cations differentially support transmitter release at the squid giant synapse.
Authors: Augustine G J , Eckert R
Published: December 2014

The ability of Ca, Sr and Ba ions to support transmitter release was studied at the squid giant synapse by examining their respective actions on presynaptic current and post‐synaptic responses. Transmitter‐induced post‐synaptic currents were smaller in Sr‐ than in Ca‐ containing solutions, and much smaller in Ba‐containing solutions. The time course and amplitude of spontaneous miniature post‐synaptic potentials were similar in the presence of all three divalent ions. Sr or Ba substitution has little effect on the resting potential of presynaptic terminals. In Sr‐containing solutions, action potentials were similar in amplitude and time course to those recorded in Ca. Ba slightly prolonged action potential duration but had no effect on amplitude. Voltage‐clamped presynaptic terminals exhibited inward Ca, Sr or Ba currents which were apparently carried through Ca channels. These currents were similar in amplitude and time course in all three ions, being somewhat larger in Ba. Although presynaptic currents were similar in these ions, transmitter release induced by these currents depended upon the divalent species entering the presynaptic terminal. Release was greatest in response to presynaptic current carried by Ca and smallest in response to current carried by Ba. Transfer curves relating presynaptic current to post‐synaptic potential were sigmoidal in all three ions, and exhibited limiting slopes of approximately 2. Divalent cations differentially support transmitter release at the squid giant synapse in the sequence Ca greater than Sr much greater than Ba. The differential efficacy of the divalent cations is not due to post‐synaptic alterations, presynaptic potential changes or differences in presynaptic divalent cation conductances. This sequence may reflect the cation selectivity of the exocytotic process responsible for transmitter release.
Acetylcholine receptors in human oocytes.
Authors: Eusebi F , Pasetto N , Siracusa G
Published: December 2014

Neurotransmitter receptors have been studied by conventional electrophysiological techniques in the membrane of human ovarian oocytes isolated from ovarian fragments obtained from pre‐menopausal women undergoing abdominal surgery for gynaecological conditions. Ovarian oocytes respond to acetylcholine (ACh) concentrations as low as 10(‐10) M by hyperpolarizing the membrane and by concomitantly increasing input resistance, in a dose‐dependent manner. The response lasts as long as the transmitter is present in the extracellular fluid. No response is elicited by ionophoretically applied ACh. The ACh response has an apparent latency of less than 1 s and a reversal potential of about ‐12 mV. The response to ACh (10(‐8) ‐ 10(‐3) M) is unaffected by curare (10(‐5) ‐ 10(‐4) g/ml) and is blocked by atropine (10(‐6) ‐ 10(‐4) g/ml). This indicates that ACh receptors in the human oocyte membrane are probably muscarinic in nature. No response is elicited by the amino acids glutamate, aspartate and glycine (up to 10(‐3) M), or by noradrenaline, adrenaline and 5‐hydroxytryptamine (up to 10(‐3) M). On the basis of analogies to the response elicited by agents which activate parthenogenetic development in the oocytes of other mammals, it is suggested that the sperm‐carried ACh might be involved in activation processes triggered by sperm‐egg interaction.
Glycogen depletion elicited in tenuissimus intrafusal muscle fibres by stimulation of static gamma‐axons in the cat.
Authors: Decorte L , Emonet-Dénand F , Harker D W , Jami L , Laporte Y
Published: December 2014

In this study the experimental conditions used to elicit glycogen depletion in tenuissimus intrafusal muscle fibres were different from those used by Barker, Emonet‐Dénand, Harker, Jami & Laporte (1976): the tenuissimus was left in situ; several (4‐6) static gamma‐axons were stimulated together; the blood flow through the muscle was not reduced during the periods of gamma stimulation except in two experiments; very much longer periods (up to 9 h) of intermittent stimulation by bursts at 50‐500/s were used. Bag1 and bag2 fibres were identified by their different ATPase activities in the B region. In two experiments with normal circulation, test responses of several primary endings to short periods of stimulation at 50‐100/s were still very strong after stimulation of several static gamma‐axons for 5 and 9 h, respectively. Glycogen depletion was observed in a large number of chain and bag2 poles but in only one of nineteen bag1 poles examined. In two other experiments with normal circulation, there was a very pronounced reduction of the test responses after stimulation of several static gamma‐axons for 7 and 9 h, respectively. Out of twenty‐four bag1 poles examined, nineteen exhibited zones of depletion. In an experiment in which stimulation was conducted as in Barker et al. (1976), i.e. with reduction of muscle blood flow during 1 min periods of stimulation at 50‐100/s, the primary endings still gave a strong response after fifteen periods of stimulation in contrast with the marked 'fatigue' that was constantly observed in the former study. No depleted intrafusal fibres were found in the spindles of this muscle. In a last experiment, after an initial pattern of stimulation similar to that described above, the new pattern of stimulation, but with periodical reduction of blood flow, was applied, leading to a 'fatigue' of the test responses in 2 h. In the spindles of this muscle three out of ten bag1 poles were depleted. The variability of glycogen depletion in bag1 fibres appears to be linked to the degree of spindle 'fatigue' which may develop after static gamma stimulation. It seems that in 'fatigued' spindles some factor or factors liberated by the contraction of neighbouring fibres may deplete glycogen in bag1 fibres by a non‐neural mechanism. When, in spite of a prolonged stimulation of static gamma‐axons, no fatigue of the test responses develops, zones of depletion in bag1 fibres‐‐possibly of neural origin‐‐are very rare, although a large proportion of bag2 and chain fibres are depleted.
Alpha‐adrenergic stimulation of potassium efflux in guinea‐pig hepatocytes may involve calcium influx and calcium release.
Authors: DeWitt L M , Putney J W
Published: December 2014

Either 86Rb or 42K appears to be a useful marker for monitoring the movement of cellular K in dispersed guinea‐pig hepatocytes. Alpha‐adrenergic stimulation of perifused hepatocytes causes a biphasic increase in 86Rb or 42K efflux from hepatocytes previously equilibrated with radio‐isotope. The first phase is a large transient (about 5 min) increase which is followed by a slowly falling phase of release. Alpha‐adrenergic stimulation of hepatocytes perifused with medium containing no added Ca plus 0.1 mM‐EGTA evokes only the transient increase in 86Rb efflux. The addition of Ca to the medium in the continued presence of agonist restores the second phase of the response. Both phases of the response appear to be mediated by alpha 1‐receptors. The magnitude of the second phase is dependent upon the concentration of Ca added to the perifusion medium. Other agonists that are believed to act by mobilizing Ca give similar results in this system. Angiotensin II, ATP and A23187 stimulate a transient increase in 86Rb efflux without extracellular Ca present, with the second phase of the response appearing upon the addition of Ca to the medium. These results suggest that the initial transient phase of 86Rb efflux, which is independent of extracellular Ca, is stimulated by Ca released from an intracellular pool. The second phase, which occurs only in the presence of extracellular Ca, is probably a result of Ca influx into the cell.
The effect of components of rabbit pulmonary surfactant on the activity of phospholipases.
Authors: Heath M F , Jacobson W
Published: December 2014

This study investigates the ability of two components of pulmonary surfactant, protein and phosphatidylglycerol, to inhibit the action of phospholipases against phosphatidylcholine. Broncho‐alveolar protein, prepared by de‐lipidation of rabbit lung lavage material had an inhibitory effect on phospholipases A1 and A2 from rabbit lung lysosomes, comparable to the effect of bovine serum albumin. The degree of inhibition was found to increase with increasing enzyme activity. De‐lipidated broncho‐alveolar protein was separated into two fractions by gel chromatography. Inhibitory activity was associated only with the second peak, corresponding to rabbit albumin. The effect of phosphatidylglycerol (PG) on the activity of phospholipases A against dipalmitoyl phosphatidylcholine and unsaturated phosphatidylcholine (USPC) was investigated, and compared with the effects of two substrate analogues on the hydrolysis of USPC. There was no indication of true inhibition by PG, but some stimulation of USPC hydrolysis by 10 mol % PG. The relevance of these findings to the fate of surfactant in vivo is discussed.
On the predictive control of foveal eye tracking and slow phases of optokinetic and vestibular nystagmus.
Authors: Yasui S , Young L R
Published: December 2014

Smooth pursuit and saccadic components of foveal visual tracking as well as more involuntary ocular movements of optokinetic (o.k.n.) and vestibular nystagmus slow phase components were investigated in man, with particular attention given to their possible input‐adaptive or predictive behaviour. Each component in question was isolated from the eye movement records through a computer‐aided procedure. The frequency response method was used with sinusoidal (predictable) and pseudo‐random (unpredictable) stimuli. When the target motion was pseudo‐random, the frequency response of pursuit eye movements revealed a large phase lead (up to about 90 degrees) at low stimulus frequencies. It is possible to interpret this result as a predictive effect, even though the stimulation was pseudo‐random and thus 'unpredictable'. The pseudo‐random‐input frequency response intrinsic to the saccadic system was estimated in an indirect way from the pursuit and composite (pursuit + saccade) frequency response data. The result was fitted well by a servo‐mechanism model, which has a simple anticipatory mechanism to compensate for the inherent neuromuscular saccadic delay by utilizing the retinal slip velocity signal. The o.k.n. slow phase also exhibited a predictive effect with sinusoidal inputs; however, pseudo‐random stimuli did not produce such phase lead as found in the pursuit case. The vestibular nystagmus slow phase showed no noticeable sign of prediction in the frequency range examined (0 approximately 0.7 Hz), in contrast to the results of the visually driven eye movements (i.e. saccade, pursuit and o.k.n. slow phase) at comparable stimulus frequencies.
Discrimination of parallel neutral amino acid transport systems in the basolateral membrane of cat salivary epithelium.
Authors: Mann G E , Yudilevich D L
Published: December 2014

Transport of short‐chain and long‐chain neutral amino acids across the basolateral membrane of the epithelium in the perfused cat salivary gland has been studied using a rapid (less than 30 s) single circulation paired‐tracer dilution technique. Amino acid uptake was measured by comparing the venous dilution profiles for a tritiated amino acid and D‐[14C]mannitol (extracellular reference) following a bolus intra‐arterial injection of a mixture containing both molecules. Unidirectional influx (v) was estimated from the maximal tracer uptake (Umax), the perfusate flow (F) and the perfusate amino acid concentration (Ca): v = [‐F . ln (1‐Umax)] . Ca. L‐alanine influx was saturable and apparently mediated by a single entry system (Km = 0.83 +/‐ 0.11 mM and Vmax = 655 +/‐ 32 nmol/min . g). These kinetic constants were considerably lower than our previously reported values for L‐phenylalanine: Km = 6.4 mM and Vmax = 1719 nmol/min . g. In cross‐inhibition experiments performed over a wide range of concentrations (0.05‐24 mM), influx of L‐alanine and L‐phenylalanine could be further discriminated, since both L‐phenylalanine (Ki = 22 mM) and L‐alanine (Ki = 19 mM) behaved as poor competitors. Removal of Na+ from the perfusate resulted in a selective inhibition of L‐alanine and L‐serine influx, whereas influx of the long‐chain neutral amino acids L‐leucine, L‐phenylalanine and L‐tryptophan remained unaffected. Although prolonged perfusion of glands with dinitrophenol (0.8 mM for 20‐30 min) caused a variable but net inhibition of unidirectional uptake, it markedly enhanced the tracer efflux of L‐leucine, L‐phenylalanine, L‐tyrosine and the basic amino acid L‐lysine. It appears that at least two separate neutral amino acid transport systems are operative at the blood‐tissue interface of the salivary epithelium: (i) a Na+‐dependent alanine‐serine‐cysteine preferring type of carrier exhibiting a high affinity for amino acids with short, polar or linear side chains and (ii) a Na+‐independent leucine preferring type of carrier selective for large neutral amino acids.
Tension maintenance, calcium content and energy production of the taenia of the guinea‐pig caecum under hypoxia.
Authors: Ishida Y , Takagi K , Urakawa N
Published: December 2014

When potassium (45.4 mM) was applied to isolated taenia of guinea‐pig caecum, the muscle developed a rapid phasic and sustained tonic tension during aerobic conditions bubbled with 95% O2:5% CO2. Under hypoxic conditions bubbled with 95% N2:5% CO2, the taenia lost its ability to respond to high potassium with sustained tonic contraction, although it still showed rapid phasic contraction. Raising the glucose concentration from 5.5 to 55.5 mM in the presence of high potassium during hypoxia caused development of a sustained contraction which was 50% that of the muscle in aerobic conditions. In the presence of high potassium, the ATP content of the taenia decreased in hypoxia, but increased with increasing glucose concentration. When the taenia was exposed to hypoxic conditions, the amount of lactate released from the muscle increased. Raising the glucose concentration caused a further increase in lactate release in the presence of high potassium under hypoxia. Good correlations (gamma greater than 0.9) were observed between tension development, the ATP content and lactate release of the taenia in the presence of high potassium under hypoxia when the glucose concentration was varied between 5.5 and 55.5 mM. The total calcium content was increased by the presence of high potassium under aerobic conditions and the increase was abolished when the muscle was exposed to hypoxic conditions. Under hypoxia the total calcium content was not increased by raising the glucose concentration in the presence of high potassium. The cellular calcium content of the taenia, determined by the lanthanum method, was increased in the presence of high potassium under aerobic and hypoxic conditions, but the content was smaller in hypoxic conditions than in aerobic conditions. Under hypoxic conditions, raising the glucose concentration in the presence of high potassium did not affect the cellular calcium content. These results suggest that under hypoxic conditions the potassium‐induced sustained contraction of the taenia is increased by raising the glucose concentration owing to increased ATP production through the glycolytic pathway, but not through mechanisms increasing the intracellular Ca concentration.
Substance P reduces acetylcholine‐induced currents in isolated bovine chromaffin cells.
Authors: Clapham D E , Neher E
Published: December 2014

Patch‐clamp techniques were used to examine the effect of substance P on acetylcholine‐induced current in bovine chromaffin cells. Cells had been enzymatically isolated and kept in short‐term culture. Experiments were performed at 22 degrees C. Under whole‐cell voltage‐clamp conditions substance P alone (2‐10 microM) did not induce ionic currents. Acetylcholine (ACh, 20 microM) at ‐60 mV induced an inward current that desensitized in the continued presence of ACh. The time course of desensitization was somewhat variable from cell to cell. In most cases it could be fitted by a single exponential with time constant of 8‐10 s. Substance P (2‐50 microM) applied simultaneously with ACh induced what appeared to be an acceleration of the desensitization process. The time course in the presence of 10 microM‐substance P (20 microM‐ACh) was best fitted by the sum of two exponentials with time constants of 0.6 s and 5 s respectively. The effect was reversible. The recovery of ACh‐induced current from desensitization was not affected by substance P. The time constant for recovery was approximately 7 s in the presence or absence of substance P. Single‐channel records showed that the conductance of individual channels was not changed by substance P. The mean open time of single channels was shortened by substance P both at high (20 microM) and at low (0.5 microM) concentrations of ACh. The inverse mean open time varied linearly with substance P concentration. Single‐channel responses appeared in bursts and clusters after almost complete desensitization at 20 microM‐ACh, as was previously observed in frog skeletal muscle. Substance P dramatically reduced ACh current by increasing interburst intervals while decreasing burst duration and the number of openings per burst. We conclude that substance P inhibits ACh‐induced depolarization of chromaffin cells either by increasing the rate of desensitization or by inducing channel blockade, which indirectly enhances desensitization. Possible models of desensitization in the absence and presence of substance P are discussed.
Sodium and potassium transport in trout (Salmo gairdneri) erythrocytes.
Authors: Bourne P K , Cossins A R
Published: December 2014

The principal pathways of Na+ and K+ transport in trout erythrocytes have been characterized. Approximately 50% of K+ influx in steady‐state erythrocytes was inhibited by ouabain (1 mM) and 46% by furosemide (1 mM). Furosemide‐sensitive K+ influx was a saturable function of external K+ concentration with a Km of 25 mM. This flux component was also inhibited by SITS (4‐acetamido‐4'‐isothiocyanatostilbene‐2'2‐disulphonate) (concentration required for 50% inhibition, I50 = 7.6 X 10(‐6)M) and by the removal of external Cl‐. An increase in cell volume stimulated furosemide‐sensitive K+ influx and cell shrinkage inhibited this flux. K+ efflux was mainly furosemide‐sensitive (64% of total). This pathway was unaffected by variations in extracellular K+ concentration and is therefore not exchange diffusion. However, it was affected by variations in cell volume in a similar way to the furosemide‐sensitive K+ influx. Na+ influx was only slightly sensitive to furosemide (13% of total) but this component was very sensitive to changes in cell volume; decreased cell volume increased Na+ influx whilst increased cell volume inhibited Na+ influx. Furosemide‐sensitive K+ influx was unaffected by variations in external Na+ concentration. Similarly, furosemide‐sensitive Na+ influx was unaffected by variations in external K+ concentration. This indicates that the passive influxes of Na+ and K+ were not coupled, in contrast to the situation in avian erythrocytes. The opposite effects of cell volume upon passive Na+ and K+ fluxes are in good agreement with the net movements of these cations during volume regulation in erythrocytes of the flounder (Cala, 1977) and the toadfish (Lauf, 1982).
Examination of the role of the electrogenic sodium pump in the adrenaline‐induced hyperpolarization of amphibian neurones.
Authors: Smith P A
Published: December 2014

The effect of adrenaline and acetylcholine (ACh) on the membrane potential of Rana pipiens sympathetic ganglia was examined by means of the sucrose gap recording technique. Adrenaline (1‐50 microM) consistently produced a hyperpolarization (Adrh) which was not reduced by Ringer solution containing 10 mM‐Mn2+, nor by Ringer solution where the Na+ concentration was reduced from 100 to 30 mM. High doses of ACh (10 mM) produced a biphasic response, a depolarization (AChd) followed by an after‐hyperpolarization (ACha.h.p.). Ringer solution containing 100 mM‐Li+ (rather than 100 mM‐Na+) or 10 microM‐ouabain blocked the ACha.h.p. and reduced the Adrh. The AChd was essentially unchanged. Ringer solution containing 0.2 mM‐K+ (rather than 2 mM‐K+) blocked part of the ACha.h.p. whereas the Adrh was enhanced. Ringer solution containing 6 mM‐K+ reduced the amplitude of the Adrh. The Adrh and the antidromically evoked action potential after‐hyperpolarization (antidromic a.h.p.) reversed polarity at approximately the same membrane potential. These data do not support the hypothesis that the Adrh results from activation of the electrogenic sodium pump. It is tempting to speculate that the response may be generated by an increase in potassium conductance (gK) which is especially sensitive to manipulations which result in sodium pump inhibition.