bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of sodium‐calcium exchange in salamander rods.
Authors: Hodgkin A L , McNaughton P A , Nunn B J
Published: December 2014

1. Methods employing suction electrodes to measure the small inward currents associated with the exchange of internal Ca2+ for external Na+ in salamander rod outer segments are described. 2. The ratio of the integral of the exchange current to the integral of the Ca2+ current during the loading period averaged 0.37, which is consistent with 1 Ca2+ ion exchanging with 2.7 Na+ ions, in approximate agreement with Yau & Nakatani (1984b). 3. The transient pumping current observed when external Na+ was restored after a few seconds in isotonic Ca2+ with IBMX (3‐isobutyl‐1‐methylxanthine) consisted of a phase with current at a constant saturated level followed by a phase in which current declined along a characteristic S‐shaped curve that was much steeper than expected from the Michaelis equation. 4. The relation between Ca2+ load and pumping current was also steeper than a Michaelis relation. 5. In Ringer solution at 20 degrees C the saturated exchange current was about 20 pA and the value of charge at which the current was half‐saturated was 1‐5 pC corresponding to 6‐30 X 10(6) Ca2+ ions per rod outer segment. 6. The Ca2+ exchange current after small loads declined along the same curve as that determined with medium loads but fell more slowly after large loads. 7. The exchange current at the beginning of the plateau of a strong flash response usually declined along the curve determined with small or medium Ca2+ loads. 8. There was evidence that the exchange current at the tip of the outer segment remained saturated for longer than at the base. 9. The time to pump out Ca2+ through the Na+‐Ca2+ exchange system is largely responsible for the delay in the recovery of the light‐sensitive current after a Ca2+ load. 10. A theoretical analysis of some of the observations in this and the succeeding paper is based on assumptions about the binding of Ca2+ by exchange sites and by cytoplasmic Ca2+ buffers.
A prolonged contraction at the end‐plate region of the diaphragm of rats and mice after anticholinesterases in vitro.
Authors: Burd P F , Ferry C B
Published: December 2014

1. Experiments have been made on the phrenic nerve and diaphragm of rats and mice in vitro at 37 degrees C. 2. The administration of the anticholinesterase drugs ecothiopate, ambenonium or neostigmine resulted in enhancement of the 'twitch' response to nerve stimulation which was often followed by a prolonged contraction lasting several seconds. 3. The prolonged contraction was localized at the end‐plate. 4. Associated with the prolonged localized contractions were prolonged end‐plate currents and prolonged end‐plate potentials. 5. Procedures which diminished transmitter release or action, i.e. high [Mg2+]o, alpha‐bungarotoxin, (+)‐tubocurarine, denervation and repetitive stimulation, also diminished or curtailed the prolonged localized contraction. 6. It is concluded that the prolonged localized contractions are due to prolonged transmitter actions as a consequence of inhibition of the acetylcholinesterase, at the end‐plate.
Short‐range elasticity and resting tension of relaxed human lower leg muscles.
Authors: Hufschmidt A , Schwaller I
Published: December 2014

1. Tension responses of relaxed human lower leg muscles were recorded during applied triangular stretch cycles at a range of constant angular velocities which were below the threshold for inducing stretch reflexes. 2. Length‐tension curves so obtained begin with a steep initial rising phase which is demonstrated to be equivalent to the 'short‐range elastic component' (s.r.e.c.) observed in resting frog muscle (Hill, 1968). The s.r.e.c. develops only gradually following a stretch‐release cycle. The time course can be described by a saturation function. It is suggested that this can be explained as resulting from a slow shift of the kinetic equilibrium between attached and detached cross‐bridges towards attached cross‐bridges. A kinetic model is presented, by which the sum of the cross‐bridge formation and decay rate constants can be calculated from the saturation curves. 3. The recovery of resting tension following a stretch‐release cycle proceeds at a significantly higher rate than the development of the s.r.e.c. Resting tension is also selectively influenced by passive movements of very small amplitude. This further suggests that the s.r.e.c. and resting tension are generated by different sources.
Muscle fibre conduction velocity in motor units of the human anterior tibial muscle: a new size principle parameter.
Authors: Andreassen S , Arendt-Nielsen L
Published: December 2014

1. Twitch contractions were elicited in human anterior tibial muscle by intramuscular microstimulation of single motor axons with a bipolar needle electrode. The population of stimulated motor units studied was fairly representative for the muscle. 2. The conduction velocity of the fibres in the motor unit was calculated as the ratio between the electrode separation (15 mm) in a tripolar array of surface electrodes and the conduction delay of the motor unit potential along the electrode array. The motor unit conduction velocity ranged from 2.6 to 5.3 m/s with a mean of 3.7 m/s. 3. The contractile properties of the motor units were obtained by averaging the torque developed around the ankle joint. Twitch torques ranged from less than 10(‐3) to 16 x 10(‐3) N m, with a mean of 5.7 x 10(‐3) N m. The twitch torque of the whole anterior tibial muscle was approximately 5 N m. Rise times were 47‐80 m/s with a mean of 61 m/s, and half‐relaxation times were 40‐78 ms with a mean of 60 ms. 4. The mechanical properties of individual motor units were highly correlated (rise time and twitch torque: r = ‐0.81; rise time and half‐relaxation time: r = 0.75; twitch torque and half‐relaxation time: r = ‐0.81). 5. The motor unit conduction velocity was highly correlated to twitch torque (r = 0.87), rise time (r = ‐0.75) and half‐relaxation time (r = ‐0.66). This indicates that the motor unit conduction velocity can be included in the family of interrelated 'size principle parameters'.
Thresholds to chromatic spots of cells in the macaque geniculate nucleus as compared to detection sensitivity in man.
Authors: Crook J M , Lee B B , Tigwell D A , Valberg A
Published: December 2014

1. The relation between wavelength and psychophysical threshold for chromatic spots on a white background provides evidence for the existence of chromatic channels in the primate visual system. To find the physiological substrate of this task, we compared increment thresholds of different cell types in the macaque lateral geniculate nucleus with human psychophysical thresholds to the same stimuli, using two spot sizes, 4 and 0.4 deg. 2. At different wavelengths, different opponent cell classes in the parvocellular layers of the nucleus were most sensitive, so that at long wavelengths (greater than 600 nm) red on‐centre cells were most sensitive, while at short wavelengths (less than 500 nm) S‐cone, blue on‐centre cells were most sensitive, from 500 to about 550 nm green on‐centre cells being most sensitive. A rare cell type with inhibition from S‐cones was most sensitive at about 570 nm, although its maximum contrast increment sensitivity was poor compared with that of other cell types. Variation in strength of cone opponency caused a considerable range in threshold in each of the opponent cell classes of the parvocellular layers. 3. On‐ and off‐centre cells from the magnocellular layers were more sensitive than opponent cells to white and yellow spots (as is the case with achromatic gratings). 4. With different wavelengths and spot sizes, the most sensitive cells found approached (to within 0.1‐0.3 log units) human psychophysical sensitivity, suggesting that the most sensitive cells available may underlie detection. 5. Measurements of psychophysical chromatic discrimination thresholds, both with nearly monochromatic spots and with spots of differing saturation (purity), support this hypothesis. When magnocellular cell sensitivity corresponded to psychophysical threshold, a suprathreshold stimulus, capable of activating opponent cells, was required for chromatic discrimination.
The involvement of inositol 1,4,5‐trisphosphate and calcium in the two‐component response to acetylcholine in Xenopus oocytes.
Authors: Gillo B , Lass Y , Nadler E , Oron Y
Published: December 2014

1. The membrane response to acetylcholine (ACh), inositol 1,4,5‐trisphosphate (IP3) and intracellular Ca2+ was studied in Xenopus laevis oocytes under voltage‐clamp conditions. 2. Shallow, submembranal injections of IP3 in the animal hemisphere of the oocyte evoked a two‐component response comprised of a rapid, transient component followed by a slow, sustained component. 3. When the injection pipette was inserted further into the cell (to 300 microns below the cell membrane), the fast component diminished and the slow component remained unchanged or even increased. 4. The rapid component exhibited an apparent higher sensitivity to IP3 compared to the slow component. 5. The two components of the IP3 response were retained in a Ca2+‐free environment. 6. Injection of a single large dose (20‐50 pmol) of CaCl2 into the oocyte evoked a typical two‐component response, whereas repetitive threshold doses (0.1 pmol CaCl2) elicited large current fluctuations which developed into a small depolarization current. 7. The delay in the peak of the slow component of the response to either IP3 or to CaCl2 injections appeared too long to be accounted for by diffusion alone. 8. Depletion of oocyte Ca2+ by the divalent cation ionophore A23187 (greater than 1 microM) inhibited the response to ACh and IP3. Low concentrations of A23187 selectively inhibited the rapid component of the ACh response, though not the rapid component of the IP3 response. 9. Our data suggest that the two‐component membrane response to ACh in Xenopus oocytes can be accounted for by ACh‐induced elevation of IP3 and subsequent IP3‐induced release of intracellular Ca2+.
Dopamine acts on D2 receptors to increase potassium conductance in neurones of the rat substantia nigra zona compacta.
Authors: Lacey M G , Mercuri N B , North R A
Published: December 2014

1. Intracellular recordings were made from neurones in the substantia nigra zona compacta in slices of rat mesencephalon in vitro. The majority of neurones fired action potentials spontaneously at 0.2‐5.6 Hz. Dopamine, applied either by superfusion or from the tip of a pressurized pipette, prevented spontaneous action potential firing and hyperpolarized the membrane. 2. When the membrane potential was held negative to the threshold for action potential firing, the hyperpolarization evoked by dopamine was accompanied by a fall in input resistance. Under voltage clamp, dopamine produced an outward membrane current associated with an increase in membrane conductance. The effects of superfused dopamine on firing rate, membrane potential and membrane current were concentration dependent in the range 1‐100 microM. 3. The reversal potential for the hyperpolarizations and the outward currents produced by dopamine was ‐109.7 +/‐ 1.7 mV (n = 12) when the potassium concentration was 2.5 mM and ‐74.0 +/‐ 5.0 mV (n = 4) when the potassium concentration was 10.5 mM. The change in reversal potentials in these and intermediate potassium concentrations was described by the Nernst equation. 4. The outward current induced by dopamine was reversibly reduced by barium (100‐300 microM) and by high concentrations of tetraethylammonium (greater than or equal to 10 mM). Calcium‐free solutions with cobalt (0.5‐2 mM) did not reduce the current in response to dopamine during the first 5 min of their application. Currents and hyperpolarizations caused by dopamine were unaffected by tetrodotoxin (1 microM). 5. The hyperpolarization produced by dopamine was mimicked by the D2 receptor agonist quinpirole (LY 171555, 0.1‐3 microM) and was blocked by the D2 receptor agonists domperidone and (‐)‐sulpiride. Agonists and antagonists at D1 receptors had no effect. 6. (‐)‐Sulpiride (30 nM‐30 microM) produced a progressive shift to the right in the concentration‐response curve to either dopamine or quinpirole. Schild analysis of the antagonism between (‐)‐sulpiride and quinpirole suggested competitive antagonism with a dissociation equilibrium constant for (‐)‐sulpiride of about 13 nM. 7. It is concluded that dopamine acts on D2 receptors on neurones of the rat substantia nigra pars compacta to increase the membrane potassium conductance.
Calcium‐dependent inactivation of potential‐dependent calcium inward current in an isolated guinea‐pig smooth muscle cell.
Authors: Ganitkevich VYa  , Shuba M F , Smirnov S V
Published: December 2014

1. Calcium current (ICa) was studied in single isolated smooth muscle cells of a guinea‐pig taenia caeci dialysed with Cs+‐containing solution to suppress K+ outward current. 2. With increasing step depolarizations up to +10 mV, acceleration of ICa inactivation was observed. With further increase of step depolarization, ICa inactivation was slowed down. The largest ICa (observed at +10 mV) was characterized by the maximal speed of inactivation. 3. Comparison of ICa in different external concentrations of Ca2+ ions ([Ca2+]o) revealed that at the same membrane potential the time course of ICa inactivation was slower, the smaller the amplitude of ICa. Slowing down of ICa inactivation was observed also during its partial block by Co2+ ions. 4. Elevation of temperature increased ICa peak amplitude and accelerated its decay. The amplitude of ICa was increased by a factor of 1.7 +/‐ 0.14 (n = 6) when the temperature was raised by 10 degrees C. 5. Calculations of Ca2+ entry during ICa as a time integral of Co2+‐sensitive current, and comparison with the degree of ICa inactivation, showed that inactivation was tightly related to Ca2+ entry in the membrane potential range ‐20 to +40 mV. 6. Ba2+ current through Ca2+ channels was larger than ICa and its inactivation was considerably slower. 7. Recovery of ICa from inactivation was found to be potential dependent. When the cell membrane was hyperpolarized, ICa recovery was accelerated. 8. It was concluded that inactivation and recovery of ICa in smooth muscle cells were influenced by both Ca2+ entry and membrane potential. It was also pointed out that the observed events are difficult to explain by the hypothesis that inactivation was produced simply by accumulation of Ca2+ ions near the inner side of the membrane, and that recovery was due to lowering of internal free Ca2+ ion concentration ([Ca2+]i).
A phosphorus nuclear magnetic resonance study of metabolites and intracellular pH in rabbit vascular smooth muscle.
Authors: Spurway N C , Wray S
Published: December 2014

1. 31P nuclear magnetic resonance (n.m.r.) spectroscopy was used to investigate metabolites, intracellular pH (pHi) and the effects of pHi on tone in rabbit blood vessels. The vessels were bathed in mammalian Ringer solution and maintained at 20 degrees C while inside the spectrometer. 2. Vascular spectra showed relatively low phosphocreatine (PCr) concentrations compared to skeletal muscle. The [PCr]/[ATP] ratio was only 1.32 +/‐ 0.09 (n = 7). There was also a prominent phosphomonoester (PME) peak. Similar features have been reported for other smooth muscles examined by 31P n.m.r. 3. The [PCr] was higher and the inorganic phosphate (Pi) concentration lower than values deduced from chemical analysis of arterial extracts. However, the [PCr] value fell within the range obtained for other smooth muscles when studied by 31P n.m.r. 4. Measurement of pHi under control conditions (external pH 7.25) gave a mean value of 7.19 +/‐ 0.03 at 20 degrees C (n = 5). Metabolic inhibition brought about by 0.5 mM‐cyanide and 0.2 mM‐fluoride did not significantly alter pHi. At higher inhibitor concentrations (3 and 1 mM respectively) there was a significant acidosis. 5. The effects of NH4Cl upon pH were investigated in metabolically inhibited preparations. During 10 min applications of 30 mM‐NH4Cl (isosmotically substituted for NaCl) the pHi rose; during subsequent NH4Cl removal it fell below control values. In the least inhibited tissues the total pHi excursion between NH4Cl applications and removals was 0.5 unit. 6. Rabbit ear vessels have been found to increase vascular tone during manoeuvres which were expected to decrease pHi. From the direct measurement of pHi reported in this study, it is concluded that the vascular tone changes brought about by NH4Cl application and withdrawal may be attributed to the alteration of pHi.
Cardiovascular and respiratory responses evoked from the posterior cerebellar cortex and fastigial nucleus in the cat.
Authors: Bradley D J , Pascoe J P , Paton J F , Spyer K M
Published: December 2014

1. In both anaesthetized and decerebrate cats the cerebellar cortex (lobules VI, VII, VIII, IX and X) and the fastigial nucleus (f.n.) have been stimulated electrically, and chemically, while recording changes in phrenic nerve discharge, heart rate, arterial blood pressure and renal and femoral blood flow. 2. Stimulation of lobules VI, VII, VIII and Xb failed to elicit any cardiovascular or respiratory changes. Activation of lobule IX (the uvula), and in some preparations sub‐lobule Xa, evoked cardiovascular and respiratory responses consistently. In the anaesthetized cat, electrical stimulation of the uvula evoked apnoea, a small bradycardia and a depressor response associated with vasodilatation in the hindlimb vascular bed. In contrast, stimulation in an equivalent region in a decerebrate preparation elicited an apneustic discharge, a pronounced tachycardia and a rise in arterial pressure with vasoconstriction in both renal and femoral vascular beds. In both the anaesthetized and decerebrate animals the pattern of response elicited by chemical activation was identical to that seen with electrical stimulation. 3. Electrical, or chemical, stimulation after administration of anaesthetic to the decerebrate cat then evoked an identical pattern of response to that seen in the 'intact' anaesthetized animal. This evidence suggests that the reversal in the pattern of the response in an effect of the anaesthetic agent and not the decerebration itself. 4. The only area of the f.n. to produce cardiovascular effects was the rostral region. Electrical stimulation of the rostral f.n. in both anaesthetized and decerebrate preparations inhibited central inspiratory activity and evoked tachycardia, along with a pressor response associated with vasoconstriction in both renal and femoral vascular beds. In contrast, chemical excitation of those sites in the rostral f.n. shown previously to produce pronounced cardiovascular and respiratory changes failed to elicit any changes in the recorded variables. 5. The present evidence suggests that there are two areas in the cat cerebellum which can exert pronounced cardiovascular and respiratory effects. The patterns of response elicited by electrical stimulation of the posterior cortex and rostral f.n. are mediated by two separate cerebellar‐brainstem pathways as judged by the two different effects of anaesthesia on the evoked responses. We suggest that the f.n. may not play a role in the control of the cardiovascular system since chemical excitation of cell bodies of the rostral f.n. failed to elicit the so‐called 'fastigial pressor response'.
Effect of periglandular ionic composition and transport inhibitors on rhesus monkey eccrine sweat gland function in vitro.
Authors: Sato F , Sato K
Published: December 2014

1. The effects of peritubular ions and transport inhibitors were studied on methacholine (MCH)‐induced sweat secretion by the isolated, cannulated monkey palm sweat glands in vitro and on the transepithelial and basolateral membrane potential (p.d.). 2. Sweat secretory rate was a curvilinear function of peritubular Na+ and Cl‐ concentration. Among the anion substitutes only Br‐ was able to totally substitute for Cl‐. Presence of HCO3‐ or H2PO4‐ in the bath was not essential. 3. Both bumetanide and furosemide inhibited sweat secretion in a dose‐dependent manner with the median effective concentration (EC50) of 3 X 10(‐6) and 3 X 10(‐5) M, respectively. 4. Bumetanide (10(‐4) M) had no significant effect on basolateral membrane p.d. but nearly abolished the transepithelial p.d. 5. Hydrochlorothiazide (HCTZ, 3 X 10(‐4) M) inhibited sweat secretion by only 35%. Inhibitors of ion exchangers amiloride (10(‐4) M) and DIDS (4,4'‐diisothiocyanostilbene‐2,2'‐disulphonic acid, 10(‐4) M) lowered sweat secretion by less than 20%. 6. Removal of peritubular K+ as well as addition of 5 mM‐Ba2+ also inhibited sweat rate. 5 mM‐Ba2+ abolished the transepithelial p.d. and depolarized the basolateral p.d. by 26 mV, although the effects of Ba2+ on sweating and the transepithelial p.d. were only transient. 7. The data raise a possibility that either the NaCl or Na+‐K+‐2Cl‐ co‐transport system or both may be involved in MCH‐induced sweat secretion, whereas the role of parallel ion exchangers, if any, may be rather minor.
Calcium dependence of voltage sensitivity in adenosine 3',5'‐cyclic phosphate‐stimulated sodium current in Pleurobranchaea.
Authors: Gillette R , Green D J
Published: December 2014

1. Ionophoretic injection of cyclic AMP into a voltage‐clamped molluscan neurone caused a transient slow inward current (Isi) whose amplitude was enhanced by depolarization. Na+‐replaced salines abolished the current, placing it with cyclic AMP‐stimulated Na+ currents of other gastropod species. 2. Isi amplitude was suppressed by extracellular Ca2+. The amplitude increased up to 4‐fold at holding potentials of ‐50 mV in nominally Ca2+‐free saline. Ion substitutions showed that Ca2+ suppressed Isi more effectively than Mg2+, Co2+, Cd2+, Mn2+, Ba2+ or Sr2+. 3. Voltage sensitivity of Isi was abolished by low‐Ca2+ salines, by the Ca2+ current blocker Co2+ and by substitution of Ba2+ or Sr2+ as Ca2+ channel current carriers. In such salines Isi showed no appreciable change in amplitude at holding potentials between ‐70 and ‐25 mV. 4. Intracellular injection of the Ca2+ chelator EGTA both augmented the amplitude of the current and its duration. EGTA injection failed to suppress the Ca2+‐dependent voltage sensitivity of Isi. Intracellular injection of concentrated 3‐N‐(morpholino) propanesulphonic acid (MOPS) pH buffer to inhibit secondary, Ca2+‐dependent intracellular acidification also failed to suppress the voltage sensitivity, as did injections of a mixed EGTA and MOPS solution. 5. While the data indicate a requirement for extracellular Ca2+ in conferring voltage sensitivity, they do not support a role for an intracellular action. An extracellular binding site for Ca2+ could mediate the voltage sensitivity, either by local depolarization‐dependent changes in extracellular Ca2+ concentration or through direct voltage‐sensitive block of the Isi channel.
Genetic and phenotypic adaptation of intestinal nutrient transport to diet in fish.
Authors: Buddington R K , Chen J W , Diamond J
Published: December 2014

1. Herbivores have higher rates of intestinal sugar transport and lower rates of amino acid transport than carnivores, if each are studied while eating their respective natural diets. It was unclear whether these species differences involve a genetic contribution, since when omnivores are switched from a high‐protein to a high‐carbohydrate diet they reversibly increase sugar transport and suppress amino acid transport. Hence we studied eight fish species of differing natural diets while all were eating the same manufactured diet. 2. Na+‐dependent L‐proline uptake and active D‐glucose uptake, measured in vitro by the everted intestinal sleeve technique, followed Michaelis‐Menten kinetics. Values of the apparent Michaelis‐Menten constant increased with values of the maximal transport rate, probably as a result of unstirred layer effects. 3. The ratio of proline to glucose uptake decreased in the sequence: carnivores greater than omnivores greater than herbivores. The intestine's uptake capacity for the non‐essential nutrient glucose was much higher in herbivores than in carnivores, correlated with species differences in carbohydrate content of the natural diet. Proline uptake varied much less among species, since species with different natural diets still have similar protein requirements. 4. Since all species were studied while eating the same diet, these species differences in uptake are not phenotypic but genetic adaptations to the different natural diets. 5. In two fish species which normally switch from carnivory towards herbivory or omnivory as they mature, we observe a 'hard‐wired' developmental change in intestinal uptake. Larger animals had lower proline uptake relative to glucose uptake than did smaller animals, even though both were being maintained on the same diet in the laboratory. 6. Carnivorous fish tend to allocate absorptive tissue to pyloric caeca or a thick mucosa, while herbivorous fish tend towards a long thin intestine.
Modulation of calcium channels of twitch skeletal muscle fibres of the frog by adrenaline and cyclic adenosine monophosphate.
Authors: Arreola J , Calvo J , García M C , Sánchez J A
Published: December 2014

1. Modulation of fast and slow Ca2+ channels of frog skeletal muscle by adrenaline (10(‐6) to 10(‐5) M) and cyclic AMP was investigated using intracellular voltage recordings in intact fibres and a voltage‐clamp technique in cut fibres. 2. In tetraethylammonium (TEA), Cl(‐)‐free Ringer solution, adrenaline increased the maximum rate of rise of Ca2+ spikes by 85% and in a similar solution, peak slow Ca2+ current (ICa,s) by 51%. 3. Application of cyclic AMP to the cut ends of fibres, produced a relative increase of ICa,s of ca. 24%. The effect was maintained for ca. 2 h. 4. Changes in the time course of ICa,s were produced by adrenaline and cyclic AMP: the limiting values of time‐to‐peak current measured as a function of membrane potential were lower (ca. 41% in adrenaline and ca. 34% in cyclic AMP) than those found in control experiments. Also, ICa,s decayed faster in the presence of adrenaline or cyclic AMP. These changes can be explained by exhaustion of Ca2+ in the lumen of transverse tubular system and do not require the assumption of kinetic variations. 5. Fast Ca2+ currents (ICa,f) which could not be blocked by nifedipine were also recorded. Cyclic AMP greatly increased the amplitude of ICa,f but had no obvious effects on ICa,f kinetics. 6. Application of catalytic subunit of cyclic AMP‐dependent protein kinase by diffusion or by pressure injection also increased the amplitude of ICa,s and ICa,f. Pressure injection brought about modifications in the time course of ICa,s that cannot be explained by depletion of Ca2+. 7. Mechanical experiments were performed on single fibres. Nominally Ca2+‐free solutions prevented the development and the maintenance of positive inotropic effect of adrenaline on twitch tension. Development of twitch potentiation was dependent upon the frequency of stimulation. Adrenaline was practically ineffective if no stimulation was applied. 8. It is concluded that both populations of Ca2+ channels are modulated by adrenergic stimulation probably via cyclic AMP, and that twitch potentiation may be mediated by a Ca2+ entry through Ca2+ channels.
The role of angiotensin II in the renal responses to somatic nerve stimulation in the rat.
Authors: Handa R K , Johns E J
Published: December 2014

1. Electrical stimulation of the brachial nerves at 3 Hz (15 V, 0.2 ms), in sodium pentobarbitone‐anaesthetized rats whose renal arterial pressure was held constant, elicited a 26% increase in systemic blood pressure, a 15% rise in heart rate, an 11% reduction in renal blood flow, did not alter glomerular filtration rate and significantly reduced absolute and fractional sodium excretions and urine flow by 44, 49 and 31%, respectively. 2. In a separate group of rats, brachial nerve stimulation at 3 Hz increased plasma renin activity approximately 2‐fold, while in animals in which the brachial nerves were not stimulated plasma renin activity did not change. 3. Following inhibition of the renin‐angiotensin system with captopril or sar‐1‐ile‐8‐angiotensin II, brachial nerve stimulation resulted in similar increases in systemic blood pressure and heart rate as in the animals with an intact renin‐angiotensin system but, in captopril‐infused rats, did not change renal haemodynamics or urine flow while absolute and fractional sodium excretions were reduced by 20 and 25%, respectively. In sar‐1‐ile‐8‐angiotensin II‐infused animals, similar nerve stimulation decreased renal blood flow by 12%, glomerular filtration rate by 7% and absolute and fractional sodium excretions and urine flow by 25, 18 and 18%, respectively. These decreases in sodium and water output were significantly smaller than those observed in animals with an intact renin‐angiotensin system. 4. Stimulation of the brachial nerves increased post‐ganglionic efferent renal nerve activity by 20% and the magnitude of this response was unaffected following inhibition of the renin‐angiotensin system. 5. The results show that low rates of brachial nerve stimulation in the rat can increase efferent renal nerve activity and result in an antinatriuresis and antidiuresis which is dependent on the presence of angiotensin II, and appears to be due to an action of angiotensin II at the level of the kidney.
Existence of calcium channels and intercellular couplings in the testosterone‐secreting cells of the mouse.
Authors: Kawa K
Published: December 2014

1. The electrophysiological properties of testosterone‐secreting cells (i.e. Leydig cells) in the mouse were studied using patch electrodes. The cells appeared solitarily or in clusters after mechanical dissociation from testes. They were confirmed to be Leydig cells on the basis of 3 beta‐hydroxysteroid dehydrogenase staining. 2. Under current‐clamp conditions in the whole‐cell configuration, Leydig cells immersed in standard saline were able to generate action potential‐like responses. The active responses occurred after cessation of membrane hyperpolarization or when cells were held in a hyperpolarized condition and stimulated with depolarizing current pulses. 3. In Leydig cells under voltage clamp, depolarizations more positive than ‐50 mV evoked transient inward currents which decayed completely during the duration of depolarization (130 ms). No obvious outward currents were evoked by pulses less positive than 30 mV. 4. The inward currents were identified as Ca2+ current, since replacement of external Ca2+ with Mn2+ reversibly diminished the current whereas Ba2+ or Sr2+ substituted for Ca2+. 5. With voltage pulses more positive than 40 mV, outward currents were evoked. The currents were dependent on K+ concentration and were blocked by quinine or tetraethylammonium. The amplitudes of outward currents were increased with raised internal Ca2+ concentration. 6. Single‐channel recordings of the outward currents revealed that the unitary conductance was 130 pS when internal K+ was 131‐143 mM and external K+ was 5 mM. The open probability of the channel showed marked dependence on the membrane potential and the internal Ca2+ concentration. Thus, the current was identified as being Ca2+‐ and membrane potential‐dependent K+ current. 7. Leydig cells within a cluster possessed distinct intercellular couplings. The mean coupling ratio obtained by applying two patch electrodes to a pair of cells was 0.84. Transfer of injected dye (Lucifer Yellow) to adjacent cells was also confirmed. 8. It was concluded that Leydig cells have at least two kinds of voltage‐dependent channels in the membrane. The Ca2+ channel may be activated by physiological changes in membrane potential, leading to an influx of Ca2+. The Ca2+‐dependent K+ channel hardly seems to be activated unless the internal Ca2+ concentration increases remarkably. It is presumed that intercellular coupling may play a role in synchronizing or intensifying the endocrine activities of Leydig cells located within a cluster.
Protein kinase C activators inhibit the inositol trisphosphate‐mediated muscarinic current responses in rat lacrimal cells.
Authors: Llano I , Marty A
Published: December 2014

1. Pre‐incubation (1‐5 min) with 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA, 8‐16 nM), a tumour‐promoting phorbol ester known to activate protein kinase C, was found to inhibit acetylcholine‐induced Ca2+‐dependent K+ and Cl‐ currents in cells isolated from rat lacrimal glands. 2. Previous work showed that the same currents may be elicited by dialysing cells with a high‐Ca2+ (1.0 microM) solution, with inositol trisphosphate (InsP3), or with guanosine 5'‐[gamma‐thio]triphosphate (GTP‐gamma‐S). 3. After TPA incubation both types of currents could be elicited by dialysis with elevated Ca2+ solutions, although the magnitude of the K+ current was slightly reduced in comparison with control cells. 4. Responses to intracellular dialysis with InsP3 (20 microM) were similar to those in untreated cells, indicating that the Ca2+ release process was unaffected. 5. However, the response to GTP‐gamma‐S (0.2‐0.5 mM) dialysis was strongly inhibited in TPA‐treated cells. 6. These results suggest that protein kinase C exerts an inhibitory action on the pathway leading from receptor activation to inositol trisphosphate production.
Characteristics of C fibre baroreceptors in the carotid sinus of dogs.
Authors: Coleridge H M , Coleridge J C , Schultz H D
Published: December 2014

1. We compared the pressure‐response characteristics of C fibre and A fibre baroreceptors in the carotid sinus of anaesthetized dogs, recording impulses from the sinus nerve and varying mean pressure in the vascularly isolated sinus, which was distended with a pulsatile pressure. Functional stimulus‐response curves were obtained by gradually increasing sinus pressure above and decreasing it below a set‐point of 100 mmHg. Baroreceptors were identified by a pulsatile discharge synchronous with the pulsations in sinus pressure. A and C fibre baroreceptors were identified by the conduction velocities and blocking temperatures of their axons. 2. The pressure‐response characteristics of C and A fibre baroreceptors differed in several respects. C fibres had a pulsatile firing threshold 50 mmHg higher than that of A fibres (105.8 +/‐ 1.8 and 54.6 +/‐ 2.9 mmHg, respectively), an average maximal sensitivity 35% of that of A fibres (0.39 and 1.12 impulses s‐1 mmHg‐1, respectively), and a maximal frequency (at 220 mmHg) 29% of that of A fibres (24.5 and 84.3 impulses/s, respectively). Although invariably pulsatile at pressures above threshold, the firing pattern of C fibre baroreceptors tended to be more irregular than that of their A fibre counterparts. 3. Impulses were also recorded from C fibres that were stimulated by increasing sinus pressure but had an irregular, non‐pulsatile discharge, a high pressure threshold (averaging 154.1 +/‐ 7.2 mmHg), and a low maximum frequency (10.8 +/‐ 2.4 impulses/s). 4. Cooling the sinus nerve progressively attenuated conduction in both A and C fibres, A fibres being blocked between 12 and 4 degrees C (mean 6.8 degrees C) and C fibres between 4 and ‐1.5 degrees C (mean 1.0 degree C). Although cooling the sinus nerve to 7 degrees C did not block conduction in all A fibres, impulse activity in baroreceptor A fibres at a carotid sinus pressure of 200 mmHg was no greater than that at a pressure of 75 mmHg. By contrast, at 7 degrees C baroreceptor C fibres still provided a signal proportional to sinus pressure. 5. Our results suggest that A and C fibre baroreceptors subserve different reflex functions, the former signalling changes in arterial pressure both above and below the normal set‐point, the latter only changes above. They also suggest that differential cold blockade may be a useful tool to determine the contribution of C fibre baroreceptors to cardiovascular reflexes.
Pharmacological and physiological properties of the after‐hyperpolarization current of bullfrog ganglion neurones.
Authors: Goh J W , Pennefather P S
Published: December 2014

1. The slowly decaying, calcium‐dependent after‐hyperpolarization (a.h.p.) that follows action potentials in bullfrog ganglion B cells has previously been shown to be generated by a potassium current called IAHP. We have recorded IAHP using a switched, single‐electrode hybrid clamp where current‐clamp mode was changed to voltage‐clamp mode immediately after repolarization of a spike or the last spike of a train. 2. Reduction of extracellular calcium reduced the decay time of IAHP following a single spike. At all levels of extracellular calcium tested (0.5‐4 mM), the decay time of IAHP was longer following a train of action potentials than following a single action potential. Thus, the time course of IAHP evoked by action potentials is a function of the calcium load induced by the action potentials. Conversely, agents that reduce the amount of IAHP activated without affecting its rate of decay, probably do not affect calcium influx. 3. Muscarine (2 or 10 microM) inhibits IAHP following an action potential by at most 30% and has no effect on decay rate of IAHP. These results suggest that muscarine has little or no effect on either calcium influx or sequestration. Decay of the a.h.p. is accelerated by muscarine but this effect is due to an increased leak conductance. 4. Charybdotoxin (CTX) between 4 and 20 nM, prolongs action potential duration in a manner consistent with blockade of the voltage‐ and calcium‐dependent potassium current (Ic) involved in spike repolarization in these cells. This action is consistent with its reported action on analogous channels in other systems. However, CTX also reduces IAHP. Thus, in bullfrog ganglion neurones, two distinct calcium‐dependent potassium currents exhibit a comparable sensitivity to CTX. This cannot be due to a decreased influx of calcium because the decay rate of IAHP following an action potential is unchanged. The action of CTX was observed with both crude and purified preparations of CTX. 5. Apamin (25 nM) and (+)‐tubocurarine (concentration giving 50% of maximal inhibition = 20 microM) block IAHP without affecting action potential duration. The action of (+)‐tubocurarine is more readily reversible than apamin. Approximately 20% of IAHP is resistant to blockade by either apamin or (+)‐tubocurarine. 6. Muscarine was used to block the M‐current (IM) selectively and (+)‐tubocurarine was used to inhibit IAHP selectively. Both currents were shown to contribute to spike frequency adaptation. Inhibition of both IM and IAHP has a synergistic action to increase repetitive firing.
Analysis of cardiovascular responses evoked following changes in peripheral chemoreceptor activity in the rat.
Authors: Marshall J M
Published: December 2014

1. Comparisons have been made between rats anaesthetized with pentobarbitone and Saffan (Glaxovet), of respiratory and cardiovascular changes evoked by (1) brief stimulation of carotid body chemoreceptors (c.b.); (2) systemic hypoxia induced by N2 breathing for 5 s; (3) brief unloading of peripheral chemoreceptors with dopamine; and (4) O2 breathing for 10 s. The results are discussed in relation to responses reported in other species. 2. Under pentobarbitone, c.b. stimulation evoked hyperventilation, tachycardia, and vasoconstriction in hindlimb muscle and renal and mesenteric circulation. The effects of vagotomy and/or of holding ventilation constant indicated that the primary cardiac response to c.b. stimulation was bradycardia which could be overcome by tachycardia, due to a reflex mediated by pulmonary stretch receptors with vagal afferents and to other secondary effects of hyperventilation. However, reflex vasodilatation initiated by hyperventilation did not modulate the chemoreceptor‐induced peripheral vasoconstriction. 3. Under light pentobarbitone, N2 evoked a similar pattern of response to c.b. stimulation, except that the tachycardia apparently also reflected the known effects of increased central inspiratory drive and central nervous hypoxia on cardiac vagal and sympathetic activity. However, under deep pentobarbitone or after guanethidine, N2 induced generalized vasodilatation. It is proposed that these responses reflected the local vasodilator actions of hypoxia. 4. Under light Saffan anaesthesia, both c.b. stimulation and N2 evoked the autonomic components of the alerting stage of the defence response which includes tachycardia and vasodilatation in hindlimb muscle, which are not secondary to hyperventilation, with renal and mesenteric vasoconstriction, pupillary dilatation and exophthalmus. However, under deep Saffan anaesthesia, c.b. stimulation and N2 produced the patterns of response they each evoked under deep pentobarbitone. It is proposed that light Saffan anaesthesia allows chemoreceptor stimulation to activate the defence areas and that under such conditions the primary response to c.b. stimulation and direct effects of hypoxia may be overridden. 5. Under pentobarbitone or Saffan, the hypoventilation induced by I.V. dopamine and by O2 indicated that almost 50% of eupnoeic ventilation was due to drive from peripheral chemoreceptors. This drive apparently played no significant role in setting the baseline level of heart rate, but could account for 10% of total peripheral resistance and of the baseline level of arterial pressure under Saffan, rather less under pentobarbitone.
Kinetics and components of the flash photocurrent of isolated retinal rods of the larval salamander, Ambystoma tigrinum.
Authors: Cobbs W H , Pugh E N
Published: December 2014

1. Membrane currents initiated by intense, 20 microseconds flashes (photocurrents) were recorded from isolated salamander rods by combined extracellular suction electrodes and intracellular tight‐seal electrodes either in current or voltage clamp mode. The magnitudes (mean +/‐ 2 S.E.M.) of the maximal photoresponses recorded by the suction and by the intracellular electrode respectively were 40 +/‐ 5 pA (n = 18) and 35 +/‐ 7 mV (n = 8) for current clamp at zero current; 43 +/‐ 9 pA and 66 +/‐ 13 (n = 11) pA for voltage clamp at the zero‐current holding potential, ‐24 +/‐ 3 mV. 2. Photocurrents initiated by flashes isomerizing 0.1% or more of the outer segment's rhodopsin achieved a saturated velocity and were 95% complete in less than 50 ms. The effect of incrementing flash intensity above 0.1% isomerization can be described as a translation of the photocurrent along the time axis towards the origin. Within the interval 0‐50 ms the latter two‐thirds of the velocity‐saturated photocurrent is well described as a single‐exponential decay. The decay was much faster in voltage clamp (2.8 +/‐ 1.2 ms, n = 11) than in current clamp mode (17 +/‐ 5 ms, n = 17). 3. The initial third of the velocity‐saturated photocurrent, occurring over the interval from the flash to the onset of exponential decay, followed about the same time course in current and voltage clamp. The time interval occupied by this initial 'latent' phase decreased with increasing flash intensity and attained an apparent minimum of about 7 ms in response to flashes isomerizing 10% or more of the rhodopsin at ca. 22 degrees C. 4. The hypothesis that the decay of outer segment light‐sensitive membrane current is the same in current and voltage clamp was supported by an analysis of the difference between outer segment currents measured successively in the two recording modes. First, the tail of the difference current decayed exponentially with a time constant approximately equal to R x C, where R and C are independently estimated slope resistance and capacitance of the rod. Secondly, the integral of the difference current, when divided by outer segment capacitance, closely approximated the hyperpolarizing light response measured under current clamp. Thus, displacement current accounted for the difference between photocurrents measured in current and voltage clamp.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of interrupting the renin‐angiotensin system on sodium excretion in man.
Authors: Brown J
Published: December 2014

1. Twelve normal volunteers were studied on 2 separate days, having taken a range of diets providing 50‐300 mmol sodium per day for 3 days and having been dehydrated overnight. Each volunteer received a background intravenous infusion of arginine vasopressin (5 x 10(‐7) i.u. kg‐1 min‐1) on both days, and also received 6 mg captopril orally on one day and a placebo tablet on the other. The ensuing changes in arterial pressure, and in urinary solute and solute‐free water excretion were recorded. 2. Captopril did not significantly alter arterial pressure. It increased the rate of excretion of sodium but not of potassium, and it did not significantly change urinary osmolality or creatinine clearance. 3. Captopril increased the rate of solute‐free water reabsorption and did so in direct proportion to its effect of increasing sodium excretion. 4. A further twelve normal, dehydrated volunteers on free diets were studied on each of 2 days, after taking 500 mg lithium carbonate on the previous evening. On each day, they also received a loading dose and maintenance infusion of inulin. On one day they received 50 mg captopril orally, and, on the other, they received a placebo tablet. The arterial pressure, urinary excretion of electrolytes, and inulin clearance were recorded. 5. Captopril increased the rates of excretion of sodium, lithium and potassium, but there were no significant changes in inulin clearance or arterial pressure. 6. The natriuretic effect of captopril in either group of twelve volunteers was not significantly less in those volunteers who were already excreting more sodium, at least over the range of dietary sodium loading to which the volunteers were subjected. 7. Six normal volunteers were studied on a further 2 days, having taken a diet supplying 30 mmol sodium per day for 3 days and being dehydrated overnight. Each volunteer received a background intravenous infusion of arginine vasopressin (5 x 10(‐7) i.u. kg‐1 min‐1) on both days and also received an intravenous infusion of saralasin acetate (50 ng kg‐1 min‐1) plus carrier on one day and carrier alone on the other. The ensuing changes in arterial pressure, and in urinary solute and solute‐free water excretion were recorded. 8. There was a small but significant fall in systolic arterial pressure during the infusion of saralasin.(ABSTRACT TRUNCATED AT 400 WORDS)
Three kinetically distinct potassium channels in mouse neuroblastoma cells.
Authors: Quandt F N
Published: December 2014

1. Mouse neuroblastoma cells were utilized to examine the electrical properties of single K+ channels which might underlie multiple components of outward current in vertebrate neurones. The conductance, kinetics of activation, inactivation, and pharmacology of three types of channels were compared. 2. Two types of voltage‐dependent channels, primarily permeable to K+, were identified which did not require the presence of internal Ca2+. The first had gating kinetics best classified as a delayed rectifier. The conductance of the open channel was 35 pS (22 degrees C) in solutions having symmetrical 125 mM‐K+ concentrations. 3. The second type of channel had a conductance of 14 pS under identical conditions. The gating kinetics of this type of channel were distinct from those of the delayed rectifier. The mean first latency, and lifetime of the open state at any voltage, were longer. The maximum probability of an open channel was smaller, so that this parameter appeared less sensitive to the membrane potential. The rate of inactivation of the channel was slower. Further, at the more negative membrane potentials tested, the level of steady‐state inactivation was less for this type of channel. 4. The delayed rectifier channel was more sensitive to the blocking action of 4‐aminopyridine than the channel with low conductance. 5. A Ca2+ ‐activated, voltage‐dependent K+ channel, having a conductance of 140 pS, was also identified. The maximum probability of an open channel increased, and the voltage for half‐maximal activation shifted to a more negative potential as the internal Ca2+ was increased. 6. The time course of inactivation of K+ currents recorded from the whole cell declined in two phases, probably due to the presence of the two types of voltage‐dependent K+ channels.