bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of naloxone on haemodynamic responses to acute blood loss in unanaesthetized rabbits.
Authors: Ludbrook J , Rutter P C
Published: December 2014

1. We have tested the hypothesis that the pressor action of (‐) naloxone HC1 after haemorrhage is due to antagonism of endogenous opiate mechanisms that are activated by haemorrhage, rather than to some more direct vasoconstrictor action of the drug. 2. Six conscious rabbits were treated intravenously with either naloxone (4 mg kg‐1, then 0.1 mg kg‐1 min‐1) or equivalent volumes of saline. In unbled rabbits the naloxone regimen had no effect except to cause a transient bradycardia. After each treatment the rabbits were bled at a rate of 2.45 ml kg‐1 min‐1 until blood pressure fell to 40 mmHg or 28 ml kg‐1 of blood had been withdrawn (17‐24 ml kg‐1 after saline, 21‐28 ml kg‐1 after naloxone). 3. Throughout both episodes of bleeding there was a progressive fall of cardiac output and rise of heart rate, at rates that were constant and independent of the prior treatment. 4. After saline treatment, bleeding at first resulted in a steep and progressive fall of systemic vascular conductance and a small fall in blood pressure. However, when blood loss exceeded 12.7 ml kg‐1 (approximately 28% of blood volume) there was an abrupt rise in systemic vascular conductance and an abrupt fall in blood pressure. 5. After naloxone treatment, during the entire period of bleeding systemic vascular conductance fell steeply and blood pressure fell slowly. 6. The different effects of saline and naloxone on the haemodynamic responses to acute blood loss were not explicable by differences in haematocrit or net blood volume. 7. We conclude that endogenous opiate mechanisms are responsible for the abrupt vasodilation that occurs when more than 28% of blood volume is withdrawn rapidly from conscious rabbits. We suggest that these mechanisms reside in the central nervous system.
Effects of D‐glucose, 2‐deoxy‐D‐glucose and D‐xylose on renal function in the rat.
Authors: Garland H O , Singh H J
Published: December 2014

1. Standard renal clearance techniques were used to investigate the effects of 2.5, 5 and 10% D‐glucose, 2.5% 2‐deoxy‐D‐glucose and 2.5% D‐xylose on kidney function in male rats. 2. There was no consistent effect of D‐glucose on urinary sodium output except with 10% D‐glucose, where sodium excretion was raised compared to controls. 3. An increased urinary calcium output was seen in all D‐glucose‐infused rats compared to controls. Values obtained for 2.5, 5 and 10% glucose were respectively 32, 61 and 58% above control data. Neither 2‐deoxy‐D‐glucose nor D‐xylose produced a calciuresis. 4. The increased urinary calcium excretion in D‐glucose rats was the result of a reduction in fractional calcium reabsorption. Glomerular filtration rate (GFR) was unchanged. It was not dependent upon glycosuria or a diuresis.
Interaction of magnesium with the sodium pump of the human red cell.
Authors: Sachs J R
Published: December 2014

1. In broken red cell membranes, Mg2+ inhibition of Na+,K+‐adenosine‐5'‐triphosphatase (Na+,K+‐ATPase) activity was partially competitive with MgATP. Mg2+ inhibition of Na+,K+‐ATPase activity was uncompetitive with K+ in broken red cell membranes, and Mg2+ inhibition of ouabain‐sensitive K+ influx in K+‐free resealed ghosts was uncompetitive with external K+. 2. When Na+,K+‐ATPase activity was measured at relatively high K+ concentration, Mg2+ inhibition was partially competitive with Na+. Mg2+ inhibition of ouabain‐sensitive K+ influx in K+‐free resealed ghosts was competitive with cell Na+. Magnesium was a more effective inhibitor of the uncoupled Na+ efflux in low‐Na+ ghosts than in high‐Na+ ghosts. 3. These findings indicate that Mg2+ inhibition results from combination of the ion with the enzyme form E2K at high intracellular Na+ and K+, and from combination with the form E1 at low intracellular Na+ and K+. 4. In ghosts containing high concentrations of MgPO4, inhibition of the K+‐K+ exchange by Mg2+ was more effective at high than at low nucleotide concentrations. At high MgPO4 and low Mg2+ concentration the activity of the exchange increased monotonically with nucleotide concentration, but at a higher Mg2+ concentration, nucleotide activation of the exchange was biphasic: the K+‐K+ exchange rate increased, reached a maximum, and then decreased with increasing nucleotide concentration.
Opioid modulation of the response of preoptic neurones to stimulation of the ventral noradrenergic tract in female rats.
Authors: Dyer R G , Grossman R
Published: December 2014

1. Experiments were undertaken on twenty‐nine ovariectomized female rats, pretreated with oestrogen and anaesthetized with urethane, to test the hypothesis that opioid peptides regulate noradrenergic transmission in the medial preoptic area and thereby influence the neural circuitry controlling the secretion of luteinizing hormone. 2. Extracellular recordings were obtained with glass micropipettes from ninety‐four neurones in the medial preoptic area. These recordings were continued whilst both the ventral noradrenergic tract, the noradrenergic projection to the medial preoptic area, and orthodromic pathways originating in the arcuate nucleus, the main source for endogenous opioid peptides in the hypothalamus, were stimulated electrically. Forty of the ninety‐four neurones responded to stimulation at one or both of the test sites. 3. Electrical stimulation of the ventral noradrenergic tract excited fifteen neurones (greater than 30% change in number of action potentials recorded during the 'response time period') and inhibited a further ten cells. When the nucleus arcuatus was stimulated electrically thirteen cells were inhibited and twelve neurones showed an excitatory response. 4. The opioid antagonist naloxone (80 mM) and/or morphine (50 mM) were ejected into the immediate vicinity of eighty‐six of the recorded cells by passage of balanced currents (range 15‐80 nA) through a multi‐barrelled electrode glued to the recording electrode. The tip of the drug‐containing electrode was about 15‐25 microns behind the tip of the recording electrode. 5. The ionophoretic application of naloxone, during electrical stimulation of the ventral noradrenergic tract, diminished the inhibitory response in four of ten cells and enhanced the excitatory response in nine out of fifteen neurones. By contrast, morphine diminished the excitatory response in seven of these fifteen cells tested, an effect that was prevented by the simultaneous application of naloxone. 6. Similarly, the application of naloxone during stimulation of the nucleus arcuatus reduced the inhibitory effect in eight out of thirteen cells. When four of these eight responsive neurones were exposed to morphine either the effect of naloxone was reversed or, when given alone, the inhibition was enhanced. 7. Finally, for seventeen cells categorized as non‐responsive to stimulation at either site, the application of naloxone during hind brain stimulation revealed an excitatory input from the ventral noradrenergic tract in seven cases. 8 The experiments demonstrate that opioid peptides modulate the neural inputs to the medial preoptic area arising from the nucleus arcuatus and the ventral noradrenergic tract.(ABSTRACT TRUNCATED AT 400 WORDS)
Subunit composition of the spontaneous miniature end‐plate currents at the mouse neuromuscular junction.
Authors: Erxleben C , Kriebel M E
Published: December 2014

1. Adult, neonate and young mouse diaphragm muscle fibres were voltage clamped with a two‐electrode clamp. Miniature end‐plate currents (MEPCs) were recorded on magnetic tape and analysed with a computer. The MEPC amplitude, charge, rise time, time‐to‐peak, decay time constant and root mean square (r.m.s.) noise level were determined for each MEPC. 2. The MEPC amplitude and charge distributions showed integral peaks starting from zero. Peaks were enhanced by selecting MEPCs with uniform time characteristics, with low noise, with increased sample size, with a curve smoothing routine and/or with a selected bin size. 3. Integral peaks were found in histograms from neonate, young and old mice. The ratio of sub‐MEPCs to bell MEPCs decreased during neonatal development. 4. The size of the peak intervals was the same in all preparations of the same developmental stage. The adult modal peak varied between 8 and 12 times the subunit value, but peak intervals were similar (0.44 +/‐ 0.04 nA). 5. Changes in the holding potential or the bath temperature, or addition of an anticholinesterase agent, changed the peak interval. 6. The number of peaks in the overall MEPC amplitude and area‐to‐peak (charge) histogram profiles were usually the same. 7. Integral peaks on MEPC amplitude profiles, notches and steps on the MEPC rising phase and changes in the overall MEPC profiles are explained by a subunit composition of the quantum of transmitter release.
Extrinsic and intrinsic neural control of pyloric sphincter pressure in the dog.
Authors: Allescher H D , Daniel E E , Dent J , Fox J E , Kostolanska F
Published: December 2014

1. In chloralose‐urethane‐anaesthetized dogs a manometric assembly was inserted via a gastrostomy to monitor pyloric pressure with a sleeve sensor. Antral and duodenal contractions were monitored with both manometric side holes and serosal strain gauges. 2. Subserosal silver wire electrodes were placed in the antrum 5 cm orad and the duodenum 3 cm aborad to the pylorus to facilitate field stimulation of intramural nerves. 3. The pylorus exerted spontaneous tone (10.8 +/‐ 4.8 mmHg) with phasic contractions occurring at a rate varying from 1‐5 min‐1 and, at times, with a superimposed higher frequency up to 15 min‐1. Atropine (30 micrograms kg‐1 I.V. and 10 micrograms I.A.) reduced and tetrodotoxin (50‐100 micrograms I.A.) enhanced the phasic activity significantly. 4. Bilateral cervical vagal section had no consistent influence on pyloric motility. 5. Stimulation of the distal ends of the cervical vagal nerves at low frequencies (0.2‐0.5 Hz, 1‐3 ms, 20 V) induced phasic pyloric contractions, which were abolished by atropine or hexamethonium (10 mg kg‐1 I.V. and 1 mg I.A.). Higher frequencies (greater than 0.7 Hz) of stimulation inhibited both phasic and tonic contractions and this inhibition was unaffected by atropine, hexamethonium, phentolamine (1.5 mg kg‐1 I.V. and 100 micrograms I.A.) or propranolol (1 mg kg‐1 I.V. and 100 micrograms I.A.). All neural responses were blocked by tetrodotoxin (50‐100 micrograms I.A.). 6. Duodenal field stimulation (0.2‐5 Hz, 0.5 ms, 40 V) induced strong phasic and tonic contractions in the pylorus. This excitation was blocked by atropine, hexamethonium, tetrodotoxin (50‐100 micrograms I.A.) or duodenal transection orad to the stimulating electrodes. 7. Antral field stimulation (0.5‐1 Hz, 0.5 ms, 40 V) completely abolished phasic activity in the pylorus and reduced tonic activity, regardless of whether the contractile activity was spontaneous or induced by neural stimulation. This inhibitory action was unaffected by atropine, hexamethonium or propranolol but was blocked by tetrodotoxin and antral transection aborad to the stimulating electrodes. Phentolamine attenuated the inhibitory effect of antral field stimulation on pyloric motility. 8. It is concluded that the distal canine pylorus exhibits myogenic tone and phasic activity which is modulated by extrinsic and intrinsic nerve pathways. Vagal nerves contain fibres, activated by different stimulus parameters which can either excite or inhibit pyloric activity. Activation of antral nerves inhibits pyloric activity, with both non‐adrenergic, non‐cholinergic and phentolamine‐sensitive pathways contributing to this inhibitory response.(ABSTRACT TRUNCATED AT 400 WORDS)
Hysteresis and the length dependence of calcium sensitivity in chemically skinned rat cardiac muscle.
Authors: Harrison S M , Lamont C , Miller D J
Published: December 2014

1. The relationship between pCa (‐log10[Ca2+]) and steady‐state isometric tension has been investigated in saponin‐ or Triton‐treated (chemically 'skinned') cardiac muscle of rat. 2. Hysteresis exists in the relationship such that the muscle is less sensitive to Ca2+ during increasing activation (as [Ca2+] is stepped upward) than during reducing activation (as [Ca2+] is stepped downward). 3. The extent of the hysteresis is insensitive to interventions that increase overall calcium sensitivity by chemical means, such as caffeine, carnosine or increased pH. 4. The extent of the hysteresis is sensitive to sarcomere length. The phenomenon is virtually absent above sarcomere lengths of about 2.2‐2.3 microns but becomes progressively greater at shorter sarcomere lengths. 5. The effect of sarcomere length on calcium sensitivity is restricted to the upward‐going (increasing activation) part of the pCa‐tension loop below 2.2 microns. The downward‐going (decreasing activation) part of the hysteretic relationship is virtually unaffected by sarcomere length up to 2.2 microns. 6. Significant alterations in sarcomere length do not occur during tension development in the experiments described here: the phenomenon is not attributable to experimental artifacts of this kind. 7. Hysteresis develops sufficiently rapidly to be consistent with a physiological relevance during the normal heart beat. 8. The effects of sarcomere length show that the phenomenon is not due to force per se since, for example, greater peak force produces less hysteresis as sarcomere length is increased towards 2.2 microns. 9. Tonicity increase (by high‐molecular‐weight dextran), which shrinks the myofilament lattice, increases calcium sensitivity but reduces the effect of sarcomere length on calcium sensitivity. 10. The results suggest that lattice shrinkage is the mechanism which accounts for hysteresis in, and the sarcomere length dependence of, calcium sensitivity in cardiac muscle.
ATP and other adenine compounds increase mechanical activity and inositol trisphosphate production in rat heart.
Authors: Legssyer A , Poggioli J , Renard D , Vassort G
Published: December 2014

1. The effects of adenosine 5'‐triphosphate (ATP) and other adenine compounds were examined on rat papillary and right ventricular muscles in the presence of 10 microM‐propranolol, 10 microM‐atropine and 0.1 microM‐prazosin or 10 microM‐phentolamine. 2. Adenosine, adenosine 5'‐monophosphate (AMP), adenosine 5'‐diphosphate (ADP), ATP and alpha,beta‐methylene ATP (APCPP) produced small positive inotropic effects, sometimes preceded by transient negative effects. 3. 8‐Phenyltheophylline (8‐PT), a P1‐purinoceptor antagonist antagonized the negative effects and increased the positive inotropy induced by ATP and adenosine. 4. In the presence of APCPP, a P2‐purinergic agonist, ATP had only negative inotropic effects. 5. Adenosine and ATP increased inositol 1, 4, 5‐ and inositol 1, 3, 4‐trisphosphate as well as inositol mono‐ and bisphosphate formation. Maximal effects were obtained at concentrations of 0.5 mM. 6. APCPP increased inositol phosphate formation while 8‐PT did not prevent the effects of adenosine and ATP. 7. It is suggested that P2‐purinoceptor activation induces both a positive inotropy and an increase in inositol‐lipid metabolism in rat ventricular muscles.
Effects of adrenalectomy and glucocorticoids on the peptides CRF‐41, AVP and oxytocin in rat hypophysial portal blood.
Authors: Fink G , Robinson I C , Tannahill L A
Published: December 2014

1. The effects of adrenalectomy (3 weeks) and dexamethasone (3 h) treatment on the release of corticotrophin‐releasing factor‐41 (CRF‐41), arginine vasopressin (AVP), oxytocin (OT), adrenocorticotrophin (ACTH) and corticosterone were studied in adult female Wistar rats. 2. The animals were anaesthetized with sodium pentobarbitone which, as assessed by the effects on the circadian rhythm of plasma ACTH and corticosterone, appeared to be a better anaesthetic than either urethane or alphaxalone for studies on the hypothalamic‐pituitary‐adrenal system. 3. Adrenalectomy increased the concentrations of ACTH in peripheral plasma and the output of CRF‐41 and AVP into hypophysial portal plasma. 4. Dexamethasone administered to adrenalectomized rats significantly reduced the concentration of ACTH in peripheral plasma and the amount of AVP released into portal plasma. However, dexamethasone did not affect the output of CRF‐41 into portal blood. 5. The output of OT into portal plasma was unaffected by either adrenalectomy or dexamethasone treatment. 6. Dexamethasone administered to adrenalectomized rats reduced significantly the ACTH response to CRF‐41. 7. These results show that the feed‐back action of glucocorticoids is mediated by two mechanisms. The increased release of ACTH which follows adrenolectomy [corrected] is produced predominantly by an increased release of both CRF‐41 and AVP into hypophysial portal blood. The intermediate negative feed‐back of glucocorticoids is produced by a reduction in the output of AVP but not CRF‐41 into portal blood and, as well, by a significant reduction in the responsiveness of the anterior pituitary gland to CRF‐41.
On the potassium conductance increase activated by GABAB and dopamine D2 receptors in rat substantia nigra neurones.
Authors: Lacey M G , Mercuri N B , North R A
Published: December 2014

1. Intracellular recordings were made from 193 substantia nigra zona compacta neurones in slices of rat mesencephalon. All cells were hyperpolarized by baclofen; this was accompanied by a fall in input resistance. Cells voltage clamped at ‐60 mV showed an outward current associated with a conductance increase in response to baclofen. The baclofen effects were concentration dependent (effective range 0.3‐30 microM); the concentration producing half the maximal effect was 1.5 microM. (‐)‐Baclofen was 300‐700 times more potent than (+)‐baclofen. 2. The potential change or membrane current caused by baclofen reversed polarity at ‐108.8 +/‐ 1.1 mV (n = 10) when the potassium ion concentration was 2.5 mM, ‐96.0 +/‐ 2.8 mV (n = 3) in 4.5 mM‐potassium and ‐76.6 +/‐ 1.7 mV (n = 5) in 10.5 mM‐potassium. The relationship between reversal potential and potassium concentration conformed to the Nernst equation. 3. Dopamine was also applied to 119 of these neurones; all exhibited either a hyperpolarization or an outward current. 4. Baclofen and dopamine outward currents were reduced reversibly by barium (100‐300 microM) and tetraethylammonium (10 mM). Superfusion for 5‐10 min with solutions presumed to block calcium currents reduced, but did not abolish, responses to baclofen. The effect of baclofen persisted in tetrodotoxin (1 microM). 5. Superfusion of gamma‐aminobutyric acid (GABA, 0.3‐3 mM) caused either membrane depolarization or hyperpolarization, accompanied by a fall in input resistance. The depolarization was mimicked by muscimol (10 microM) and blocked by bicuculline methiodide (10‐100 microM); the hyperpolarization was resistant to bicuculline. Nipecotic acid (500 microM) enhanced the effect of GABA, but was without effect upon the actions of muscimol and baclofen. 6. The effect of dopamine was enhanced by cocaine (10 microM) and antagonized by (‐)‐sulpiride (0.1‐1 microM), whereas the actions of baclofen were unaffected by cocaine or (‐)‐sulpiride. The maximum outward current produced by dopamine was approximately half that produced by baclofen. 7. Outward currents produced by dopamine were reversibly occluded by maximal outward currents caused by baclofen. 8. Baclofen and dopamine hyperpolarizations were unaffected by intracerebroventricular injection of animals with pertussis toxin. 9. Cells impaled with electrodes containing guanosine 5'‐O‐(3‐thiotriphosphate) (1 mM) were hyperpolarized by both baclofen and dopamine, but the membrane potential did not fully return to its original level when agonist application was discontinued. 10. It is concluded that activation of both dopamine D2 and GABAB receptors may increase the same potassium conductance.(ABSTRACT TRUNCATED AT 400 WORDS)
Plateau and descending limb of the sarcomere length‐tension relation in short length‐clamped segments of frog muscle fibres.
Authors: Bagni M A , Cecchi G , Colomo F , Tesi C
Published: December 2014

1. The relation between sarcomere length and tetanic tension was determined at 10‐12 degrees C for 70‐80 microns long segments of single fibres isolated from the tibialis anterior and semitendinosus muscles of the frog. Measurements of segment striation spacings were performed during fixed‐end or length‐clamp contractions by means of a laser light diffractometer. 2. At sarcomere lengths of around 2.10 microns tetanic tension rose promptly to a steady plateau, independent of the recording conditions. At greater sarcomere lengths under fixed‐end conditions the tension rise occurred in two distinct stages: an initial rapid rise followed by a much slower creep. The tension creep was entirely abolished in length‐clamp contractions. 3. The sarcomere length‐tension diagram of length‐clamped segments of tibialis anterior fibres exhibited a definite flat region between about 1.96 and 2.16 microns where tension varied by less than 1.5%. The highly linear descending limb reached zero tension at about 3.53 microns. The shift to the left by about 0.10 microns, with respect to the length‐tension diagram of length‐clamped segments of semitendinosus fibres, may be tentatively explained by assuming that thin filament lengths vary in different muscles. 4. The results are in agreement with those of a previous work by Gordon, Huxley & Julian (1966) and support the hypothesis (Huxley, 1957, 1980) that muscle tension is produced by simultaneous action of independent force generators, in proportion to the number of myosin bridges overlapped by actin filaments.
Excitation of the squid giant axon by general anaesthetics.
Authors: Haydon D A , Simon A J
Published: December 2014

1. The effects of ‘clinical’ concentrations of some general anaesthetics on the minimum stimulus required to produce an action potential in the squid giant axon have been examined as a function of time from exposure to the anaesthetic. The resting potential in these experiments was also monitored. 2. The minimum stimulus varied with time in different ways for different anaesthetics. For chloroform, diethyl ether, n‐pentanol, halothane and cyclopropane the stimulus initially declined, reached a minimum after about 3 min and then recovered to near‐normal values at 10‐15 min. For n‐pentane, cyclopentane and, to a lesser extent methoxyflurane, the stimulus often declined to such low values that the axon exhibited spontaneous action potentials which persisted until the anaesthetic was removed. For one substance, the experimental local anaesthetic diheptanoyl phosphatidylcholine, the stimulus increased considerably over the 10‐15 min required to reach the steady state. In all instances the axons reverted to normal behaviour after removal of the anaesthetic although the time course by which they did so was more variable than for the initial exposure. 3. For all anaesthetics the resting potential changed in the positive direction monotonically by ca. 1‐5 mV and reached a steady state in approximately 3 min. On removal of the anaesthetic the resting potential returned to normal, also monotonically. 4. The voltage‐gated Na+ and K+ currents were significantly affected even at the low anaesthetic concentrations used. Estimates of the changes in the Hodgkin‐Huxley parameters were obtained partly by direct experiment and partly from results previously obtained for higher anaesthetic concentrations. 5. The time dependencies of the minimum stimuli have been accounted for semi‐quantitatively in terms of the resting potential changes and the voltage shifts in the Na+ current steady‐state activation, and the time dependencies respectively of these two parameters. 6. Quantitative calculations of the resting potential changes for comparison with experiment have been made based on the changes in K+ conductance determined in the preceding paper (Haydon, Requena & Simon, 1988) and changes in the Hodgkin‐Huxley parameters of the Na+ and delayed‐rectifier K+ currents. 7. Calculations of the minimum stimulus in the steady state have been made from the experimental resting potential changes and from the anaesthetic‐affected Hodgkin‐Huxley parameters. Good agreement with the experimental stimuli was found, especially in the prediction of high and low values.
Further evidence for synaptic actions of muscle spindle secondaries in the middle lumbar segments of the cat spinal cord.
Authors: Harrison P J , Jami L , Jankowska E
Published: December 2014

1. The aim of this study has been to investigate the receptor origin of postsynaptic actions evoked by group II muscle afferents in mid‐lumbar segments of the cat spinal cord. The experiments tested the hypothesis that the afferents involved were the secondary endings of muscle spindles. 2. Spindle afferents were activated by contractions of intrafusal muscle fibres which were induced by electrical stimulation of fusimotor axons in the distal parts of transected ventral roots by one to three stimuli at 150‐500 stimuli/s. A separate series of experiments has shown that such stimuli are effective in activating a considerable proportion of muscle spindle secondaries when contractions of extrafusal muscle fibres are eliminated by differential fatigue of these fibres, provided that several fusimotor axons are stimulated simultaneously. 3. Extracellular field potentials were recorded in the dorsal horn, at such locations where synaptic actions were evoked by electrical stimulation of group II but not group Ia muscle spindle or group Ib tendon organ afferents of pretibial flexors. Effects of activation of spindle afferents following stimulation of fusimotor axons were then compared with effects evoked by electrical stimulation of group II afferents of anterior tibial or extensor digitorum longus nerves and by small stretches of these muscles. 4. Distinct field potentials were evoked by stimulation of ventral root fibres at all locations at which field potentials were obtained from group II afferents stimulated electrically. The latencies of these field potentials were in both cases shorter in the dorsal horn than in the ventral horn. 5. The appearance of these field potentials was not related to contractions of extrafusal muscle fibres and was also observed when these contractions were practically eliminated. Furthermore, their threshold and similar dependence on a potentiating effect of two to three stimuli, as found for single secondaries, allow them to be attributed to secondary endings of muscle spindles.
Intrinsic determinants of firing pattern in Purkinje cells of the turtle cerebellum in vitro.
Authors: Hounsgaard J , Midtgaard J
Published: December 2014

1. The intrinsic response properties of turtle Purkinje cells and the underlying conductances have been investigated with intradendritic and intrasomatic recordings in a slice preparation. 2. The active generation site for fast Na+ spikes was confined to the soma and for slow Ca2+ spikes to the dendrites. The configuration and generation of Ca2+ spikes was more affected by the level of extracellular K+ than were Na+ spikes. 3. Sodium spikes had a lower threshold than Ca2+ spikes at all recording sites. Sodium spike firing was abruptly initiated during depolarizing current pulses and the spike frequency increased from an early minimum to a higher steady‐state level over a period of seconds or until the occurrence of Ca2+ spikes. Calcium spikes were always delayed by at least 100 ms from the onset of a depolarizing current pulse from rest. 4. The abrupt onset of Na+ spike firing was due to a tetrodotoxin‐sensitive plateau potential. The phase of accelerating firing frequency and the delayed occurrence of Ca2+ spikes was due to a transient hyperpolarization activated by depolarization from rest or from more negative membrane potentials. The transient hyperpolarization was inactivated by depolarized holding potentials and was most probably generate by a rapidly inactivating K+ channel. 5. It is concluded that turtle Purkinje cells display the basic firing properties and underlying conductances known from Purkinje cells of other vertebrates. In turtle Purkinje cells Ca2+ spikes are actively generated in spiny dendrites and it is suggested that spiny dendrites rather than branch points are ‘hot spots’. 6. The transient hyperpolarization, not previously described in Purkinje cells, seems particularly important for regulating Ca2+‐dependent excitability.
Inactivation of calcium current in bull‐frog atrial myocytes.
Authors: Campbell D L , Giles W R , Hume J R , Shibata E F
Published: December 2014

1. A single‐microelectrode technique has been used to study the voltage dependence and the kinetics of inactivation and reactivation of a tetrodotoxin‐resistant inward current (ICa) in single cells from bull‐frog atrium. 2. In most cases the kinetics of both inactivation and reactivation can be well described as a single‐exponential process. 3. Several different observations indicate that inactivation of ICa in these cells is controlled by both voltage‐dependent and current‐dependent processes, as has been demonstrated previously in heart (Kass & Sanguinetti, 1984; Lee, Marban & Tsien, 1985) and in other tissues (Hagiwara & Byerly, 1981; Tsien, 1983; Eckert & Chad, 1984). 4. Evidence in favour of a voltage‐dependent inactivation mechanism included: (a) In paired‐pulse measurements of steady‐state inactivation (‘f infinity’) a ‘conventional’ steady‐state f infinity vs. membrane potential (Vm) relationship was obtained in the range of membrane potentials from ‐60 to 0 mV. (b) Increasing [Ca2+]o from 2.5 to 7.5 mM, which resulted in a 2‐3‐fold increase in ICa, did not produce any significant increase in the amount of inactivation. (c) Using a ‘gapped’ double‐pulse protocol non‐monotonic U‐shaped inactivation relationships were obtained, i.e. positive to approximately +20 mV some removal of inactivation occurred. However, f never approached a value near 1.00 at very depolarized potentials; it reached a maximum between 0.5 and 0.6. (d) In constant [Ca2+]o and at fixed Vm, the kinetics of ICa inactivation were independent of peak size of ICa. This was demonstrated by: (i) varying the holding potential (‐90 to ‐30 mV), (ii) using paired‐pulse ‘recovery’ protocols, and (iii) partial block by La3+ (1‐10 microM) and Cd2+ (0.1 mM). (e) Influx of Ca2+ ions was not an obligatory prerequisite for development of inactivation. In all ionic conditions (Ca2+, Sr2+, Ba2+, Na+‐free and Ca2+‐free Ringer solutions) currents displayed inactivation phenomena, although the extent and kinetics of inactivation were dependent upon ionic conditions. Outward currents recorded above the reversal potential for ICa exhibited time‐ and voltage‐dependent inactivation, and could be inactivated by brief depolarizing pre‐pulses that produced no net inward current flow. Evidence against a possible role of the electrogenic Na+‐Ca2+ exchanger in producing inactivation of these outward currents was obtained.(ABSTRACT TRUNCATED AT 400 WORDS)
Evidence for adenosine triphosphate as an excitatory transmitter in guinea‐pig, rabbit and pig urinary bladder.
Authors: Fujii K
Published: December 2014

1. The effects of alpha,beta‐methylene ATP (alpha,beta‐MeATP) on membrane properties and excitatory junction potentials (EJPs) were examined in smooth muscle cells of the guinea‐pig, rabbit and pig bladder. 2. Intracellular recording with microelectrodes was used to record membrane electrical activity from the guinea‐pig bladder. ATP (10(‐3) M) produced a rapid, large depolarization with a marked increase in spike frequency, while carbachol (10(‐4) M) or acetylcholine (ACh; 10(‐4) M) produced only a small or no depolarization with a smaller increase in spike frequency. alpha,beta‐MeATP produced a similar response to that of ATP but at a much lower concentration (5 x 10(‐6) M), and the response was transient even in the continuous presence of this agent. 3. Changes in the membrane potential and conductance elicited by alpha,beta‐MeATP were also measured with the double sucrose‐gap method. alpha,beta‐MeATP (5 x 10(‐6) M) depolarized the membrane and increased the membrane conductance in all three species, but both parameters returned to control values during continuous exposure to this agent. 4. Intracellular recording with microelectrodes showed that in the guinea‐pig bladder treatment with alpha,beta‐MeATP abolished the response to ATP, while the response to ACh was unchanged. 5. With the double sucrose‐gap method, EJPs were elicited by transmural nerve stimulation of strips of the guinea‐pig, rabbit and pig bladder and had spikes superimposed, leading to contractions. Desensitization of P2‐purinoceptors by alpha,beta‐MeATP (3‐5 x 10(‐6) M) abolished the EJPs and spikes, and reduced the contraction. Atropine (10(‐6) M) alone did not alter the EJPs but reduced the contraction. Combined application of both agents abolished the contraction. 6. It is concluded that in the guinea‐pig, rabbit and pig bladder ATP is an excitatory transmitter with ACh and EJPs are mediated by ATP.
Photocurrents of cone photoreceptors of the golden‐mantled ground squirrel.
Authors: Kraft T W
Published: December 2014

1. Visual transduction in photoreceptors of the ground squirrel, Citellus lateralis, was studied by recording membrane current from individual cones in small pieces of retina. 2. Brief flashes of light produced transient reductions of the dark current; saturating response amplitudes were up to 67 pA. A flash strength of about 11,000 photons microns‐2 at lambda max was required to give a half‐saturating response. The stimulus‐response relation was well fitted by an exponential saturation curve. Responses below 20% of maximum behaved linearly. 3. The response to a dim flash in most cells had a time to peak of 20‐30 ms and resembled the impulse response of a series of five low‐pass filters. 4. The variance of the dim‐flash response amplitude put an upper limit of 80 fA on the size of the single photon response. Estimates based on the effective collecting area suggest the single photon response to be of the order of 10 fA. 5. Flash responses of squirrel cones usually lacked the undershoot observed in primate cones, although in about 1/3 of the cells a small undershoot developed during recording. 6. Background lights slightly shortened the time to peak of the flash response and reduced the integration time. 7. Spectral sensitivity measurements showed two classes of cones with peak sensitivities at about 520 and 435 nm. Rod sensitivity peaked near 500 nm. Spectral univariance was obeyed by all three classes of cells. 8. The shapes of the spectral sensitivity curves of the rod and both types of cones were similar to each other when plotted on a log wave number scale, but differed significantly from similar plots of monkey and human cone spectra. 9. The kinetics and sensitivity of flash responses of the blue‐ and green‐sensitive cones were indistinguishable.
Electrophysiological analysis of the inactivation of sympathetic transmitter in the guinea‐pig vas deferens.
Authors: Cunnane T C , Manchanda R
Published: December 2014

1. The properties of junction potentials evoked by nerve stimulation and by local application of drugs, and currents evoked by nerve stimulation, in the smooth muscle cells of the guinea‐pig vas deferens have been investigated. The effects of temperature on these responses have been studied using intracellular and extracellular recording. 2. Local, brief (5‐15 ms) application of 10(‐4) M‐adenosine‐5'‐triphosphate (ATP) from glass micropipettes onto the surface of the vas deferens, using pressure pulses (103‐206 kPa), elicited a depolarization of the smooth muscle cell membranes which closely resembled the nerve stimulation‐evoked excitatory junction potential (EJP). 3. Local application of 10(‐4) M‐noradrenaline (NA) failed to produce any detectable membrane potential response. Junction potentials elicited by a mixture of 10(‐4) M‐ATP and 10(‐4) M‐NA (ratio by volume 1:50) in the drug ejection micropipette were similar in shape to those evoked by ATP alone. 4. Cooling the tissue from 35 to 25 degrees C did not significantly alter resting membrane potentials but resulted in a significant prolongation of the rising and decaying phases of the EJPs. Fifty per cent decay times for EJPs at 35 and 25 degrees C were (mean +/‐ S.D.) 236 +/‐ 20 and 434 +/‐ 30 ms respectively (P less than 0.01). 5. Extracellularly recorded excitatory junction currents (EJCs) elicited by nerve stimulation, believed to reflect the transmembrane current underlying the EJPs, were prolonged in parallel at low temperatures (50% decay times of EJCs at 35 and 25 degrees C: 11.73 +/‐ 3.94 and 26.15 +/‐ 8.4 ms, respectively, P less than 0.01). 6. Junction potentials evoked by locally applied, exogenous ATP were also significantly prolonged by cooling (50% decay times: 663 +/‐ 88 ms at 35 degrees C and 1955 +/‐ 79 ms at 25 degrees C, P less than 0.01). 7. Bath application of 10(‐6) M‐alpha,beta‐methylene ATP, the enzymatically stable, desensitizing analogue of ATP, reversibly abolished nerve‐evoked EJPs. Local application of 10(‐6) M‐alpha,beta‐methylene ATP led to a prolonged depolarization of the smooth muscle cells lasting between 20 and 60 s. 8. Junction potentials elicited by locally applied alpha,beta‐methylene ATP were not prolonged or otherwise significantly altered on cooling. The durations of the depolarizations were 46.0 +/‐ 12.1 s at 35 degrees C and 43.4 +/‐ 10.6 s at 25 degrees C (P greater than 0.1).(ABSTRACT TRUNCATED AT 400 WORDS)
Inward rectification in submucosal arterioles of guinea‐pig ileum.
Authors: Edwards F R , Hirst G D
Published: December 2014

1. The current‐voltage relationships of short segments of submucosal arteriole of guinea‐pig have been determined using constant current and voltage clamp techniques. 2. The current‐voltage relationships were non‐linear over the membrane potential range ‐60 to ‐90 mV, the conductance increasing with hyperpolarization. 3. The membrane potential ranges over which the membrane conductance increased were changed by changing the external concentration of potassium ions. 4. Changing the external concentrations of sodium and chloride ions had no effect on the arteriolar current‐voltage relationships. 5. The hyperpolarization‐activated conductance increase was prevented by low concentrations of barium ions. 6. It is suggested that these arterioles display potassium‐selective inward rectification and that the rectifier supplies the dominant resting potassium conductance. The properties of this rectifier are compared with those of other tissues.
Visual adaptation is highly localized in the cat's retina.
Authors: Cleland B G , Freeman A W
Published: December 2014

1. The aim of this study was to determine how the spatial pattern of steady light in a visual stimulus affects the state of adaptation of the retina. 2. Impulse rate was recorded from single X and Y ganglion cells in the cat's retina. The luminance of a narrow bar of light centred over the receptive field was modulated sinusoidally in time about a steady background, and a cell's contrast gain was measured as the ratio of impulse rate modulation to bar contrast. 3. The contrast gain of a cell was set by the background, a fixed luminance level about which luminance varied in the form of a grating; grating luminance varied sinusoidally with distance but did not vary in time. When the spatial frequency of the grating was low, contrast gain was increased by a grating with a trough centred over the receptive field, and decreased by a peak‐centred grating. 4. As the spatial frequency of the grating increased, its effect on contrast gain disappeared. For cells around 10 deg from the central area, this change occurred at spatial frequencies close to 1 cycle deg‐1. 5. For each cell the effect on contrast gain of the background's spatial frequency was compared with the spatial frequency response to a time‐varying grating. It was found that the summation area for adapting light in both X and Y cells is very close in size to an X cell centre mechanism, and that the summation area for adapting light in Y cells is therefore considerably smaller than a Y cell centre. 6. From this and other evidence it was shown that sub‐areas of the Y cell centre mechanism can be independently adapted. 7. A background grating with a trough centred over the receptive field raised contrast gain more at mid‐range spatial frequencies than at low frequencies, producing a hump in the contrast gain versus frequency curve. A peak‐centred grating reduced contrast gain more at mid‐range frequencies than at low, producing a dip. 8. The dip in the contrast gain versus frequency curve for a peak‐centred grating was always greater than the hump for a trough‐centred grating. 9. These humps and dips were interpreted in terms of a model containing two antagonistic pathways. One pathway had a smaller summation area for adapting light than the other.(ABSTRACT TRUNCATED AT 400 WORDS)
Renal haemodynamics during hyperchloraemia in the anaesthetized dog: effects of captopril.
Authors: Wilcox C S
Published: December 2014

1. An increase in plasma chloride concentration (PC1) decreases renal blood flow (RBF) and glomerular filtration rate (GFR) and inhibits the intrarenal release of renin and angiotensin II (AII). Captopril was administered to indomethacin‐treated dogs to assess the role of AII independent of prostaglandins (PGs) in the haemodynamic response to hyperchloraemia. Studies were performed on kidneys that were denervated by autotransplantation. 2. Anaesthetized greyhounds received an intrarenal infusion of 0.616 M‐sodium acetate, which was changed to 0.616 M‐NaCl (hyperchloraemia). These infusions increased the plasma sodium and osmolality at the experimental kidney by 7‐11% throughout but increased the PCl during the hypertonic NaCl infusions only (122 +/‐ 3 to 136 +/‐ 3 mM). 3. In vehicle‐treated dogs (n = 8), hyperchloraemia reduced the GFR (1.4 +/‐ 0.1 to 1.0 +/‐ 0.1 ml min‐1 kg‐1; P less than 0.05) and the RBF (13.0 +/‐ 1.4 to 8.3 +/‐ 0.6 ml min‐1 kg‐1; P less than 0.01); these changes were reversible on return to the 0.616 M‐sodium acetate infusion. Hyperchloraemia reduced the release of AII into renal lymph (2.5 +/‐ 0.9 to 1.2 +/‐ 0.4 pg min‐1 kg‐1; P less than 0.01). 4. Indomethacin (0.6 mg kg‐1 and 0.2 mg kg‐1 h‐1 intrarenally; n = 4) blunted (P less than 0.05) the Cl‐‐induced fall in RBF (10.4 +/‐ 1.1 to 8.2 +/‐ 0.6 ml min‐1 kg‐1) without changing significantly the fall in GFR or the release of AII into renal lymph.(ABSTRACT TRUNCATED AT 250 WORDS)
Oscillations of free cytosolic calcium evoked by cholinergic and catecholaminergic agonists in rat parotid acinar cells.
Authors: Gray P T
Published: December 2014

1. In single, dissociated, rat parotid acinar cells the muscarinic agonist carbachol evokes a rapid rise in cytosolic free calcium [( Ca2+]i), from near 100 nM to peak levels of up to 1 microM. In the continued presence of the agonist the response decays to a lower, maintained, level. 2. In most cells, at 22 degrees C, oscillations, with a mean frequency of 0.19 Hz, are superimposed upon this elevation of [Ca2+]i. In voltage‐clamped cells oscillations of current occur in phase with the oscillations of [Ca2+]i. 3. The oscillations occur in voltage‐clamped cells, and in the absence of extracellular Ca2+, indicating that neither voltage‐gated processes, or an influx of Ca2+ is involved. 4. Oscillation frequency is independent of carbachol concentration, in the range 100 nM to 250 microM, and furthermore, shows no relationship to the mean level of [Ca2+]i during the oscillations. 5. Stimulation with the alpha‐adrenergic agonist noradrenaline, in the presence of the beta‐blocker propanolol, evokes oscillations having the same frequency as those evoked by carbachol. 6. The oscillations show a strong temperature dependence, the frequency increasing with a Q10 of 2.8. In contrast, the amplitude of the oscillations drops from a mean of 33% of the response amplitude at 22 degrees C, and below, to 6% at 33 degrees C. Above the latter temperature oscillations are not resolvable. 7. The phorbol esters, 12‐O‐tetradecanoyl‐phorbol‐13‐acetate and 12,13‐phorbol dibutyrate (1 microM), do not affect the response to carbachol at 22 degrees C, at which temperature the oscillations are of maximum amplitude. Diacylglycerol is, therefore, unlikely to be involved in oscillation generation in these cells. 8. These observations are consistent with a model in which a negative feed‐back loop links [Ca2+]i to the mechanisms of Ca2+ elevation, possibly to the inositol 1,4,5‐trisphosphate‐sensitive Ca2+ release mechanism of the endoplasmic reticulum. If the feed‐back path involved an enzymatic step, the slowing of this step at lowered temperatures could give rise to oscillations. At body temperature such a mechanism would act to ensure that [Ca2+]i was elevated in a regulated and dose‐dependent manner.
Transmitter release at mouse motor nerve terminals mediated by temporary accumulation of intracellular barium.
Authors: Quastel D M , Saint D A
Published: December 2014

1. In isolated mouse diaphragm, tetanic nerve stimulation in the presence of Ba2+ causes an increase in frequency of MEPPs which continues as an after‐discharge or ‘tail’ of raised MEPP frequency that subsides over a period of seconds, in addition to EPPs of low quantal content. ‘Ba2+ tails’ are also seen with focal depolarization of nerve terminals in the presence of tetrodotoxin. 2. The development of ‘Ba2+ tails’ could be inhibited or blocked by neomycin, raised Mg2+, or Cd2+ present at the time of stimulation; the presence of the blocking substance during the tail itself had no effect. 3. The time course of MEPP frequency changes during and after stimulation could be expressed as a simple exponential process, with the same time constant for both the rise and the fall, by taking as the time‐dependent variable the nth root of MEPP frequency, n being 4 or 5. The time constant (tau) derived from the rate of fall of the 1/4 power of MEPP frequency during the tail was at most junctions between 3 and 6 s, and apparently unaffected by concentration of Ba2+, or of Ca2+, or by tonic depolarization of the nerve terminal. 4. The intensity of ‘Ca2+ tails’ was graded steeply with the number of stimuli applied, but was nearly independent of stimulus frequency, when train duration was kept brief compared to tau, i.e. about a second or less. The nth root of the number of MEPPs at a given time period in the tail was linearly related to the number of stimuli, when n was chosen to be 4 or 5. 5. The above data are consistent with a model in which (a) with each nerve impulse in a train there occurs the same entry of Ba2+ into the terminal, (b) transmitter release (MEPP frequency) is proportional to the fourth or fifth power of [Ba2+] at critical sites within the nerve terminal, (c) the Ba2+ leaves these sites as a first‐order process with a time constant of a few seconds. Compared to Ca2+, Ba2+ persists longer but has lower potency. 6. With variation of external [Ba2+] over the range 50 microM to 6.4 mM, apparent Ba2+ entry per nerve impulse grew linearly with concentration. 7. Evidence is presented indicating that intraterminal Ba2+ can ‘co‐operate’ with Ca2+ or La3+ in promoting transmitter release.