bluuebunny/crossref_metadata_2025 huggingface dataset:
Potassium (86Rb+) efflux from the rat submandibular gland under sodium‐free conditions in vitro.
Authors: Bovell D L , Elder H Y , Pediani J D , Wilson S M
Published: December 2014

1. Fragments of rat submandibular gland were pre‐loaded with 86Rb+, an isotopic marker of potassium transport, and rate constants for 86Rb+ efflux were determined during superfusion with a physiological salt solution. 2. In sodium‐containing solutions acetylcholine evoked a rapid and immediate increase in efflux rate. After reaching a peak value, the efflux rate initially declined rapidly, but a second, slowly declining phase to the response was also evident. The response could be resolved into Ca2(+)‐independent and Ca2(+)‐dependent phases. 3. The basal efflux rate was elevated during superfusion with solutions in which sodium had been replaced with either lithium or N‐methyl‐D‐glucammonium (NMDG+). Although lithium had a greater effect, which was absent under calcium‐free conditions, addition of calcium to initially calcium‐free, lithium‐containing solutions did not affect the rate of efflux. 4. In the presence of calcium the response to acetylcholine was augmented during exposure to lithium‐containing, sodium‐free solutions but, in contrast, slightly inhibited when NMDG+ was used as a sodium substituent. 5. The transient, calcium‐independent component of the response to acetylcholine was unaffected by exposure to lithium, whereas the calcium‐dependent phase of the response was inhibited. 6. Responsiveness to acetylcholine was reduced during superfusion with a calcium‐free, NMDG+‐containing solution. The response normally observed when extracellular Ca2+ was subsequently elevated, in the continued presence of acetylcholine, was also inhibited. Sensitivity to acetylcholine was retained, however, when the tissue was initially exposed to a solution containing approximately 20 mumol l‐1 Ca2+. The response was smaller than that evoked in sodium‐containing solutions. 7. The use of lithium as a sodium substituent presents special problems, possibly related to the effects of this ion on the metabolic cycling of phosphatidylinositol‐4,5‐bisphosphate metabolites.
Reduction by baclofen of monosynaptic EPSPs in lumbosacral motoneurones of the anaesthetized cat.
Authors: Edwards F R , Harrison P J , Jack J J , Kullmann D M
Published: December 2014

1. Monosynaptic excitatory postsynaptic potentials (EPSPs) were elicited in lumbosacral motoneurones of pentobarbitone anaesthetized cats by stimulating group Ia muscle afferents with most of the dorsal roots severed. In some experiments Ia EPSPs were recorded together with monosynaptic EPSPs elicited by stimulating the ipsilateral ventral quadrants (VQ) of the thoracic spinal cord. Injection of (+/‐) baclofen (1 mg kg‐1 I.V.) caused a reduction in the peak amplitudes of both Ia and VQ EPSPs, which started immediately upon injection and progressed gradually. No recovery in EPSP amplitude was seen during the recording period, which lasted up to 60 min. 2. The Ia EPSP peak amplitude was reduced by 18‐61% (mean +/‐ S.D., 38 +/‐ 14%; n = 30), while VQ EPSPs were reduced by 7‐42% (23 +/‐ 13%; n = 5). Baclofen had a significantly larger effect on Ia EPSPs than VQ EPSPs (P less than 0.001; t test). 3. Baclofen did not cause any consistent change in the membrane potential, nor in the membrane time constant, as estimated from the exponential decay of the tail of the EPSP. There was no tendency for the reduction in peak EPSP amplitude to be related to the estimated electrical distance on the dendritic tree at which the synaptic current was injected. 4. For two I a and two VQ EPSPs, the trial‐to‐trial fluctuation in the peak amplitude was resolved into quantal parameters before and after baclofen was administered. The reduction in peak amplitude was in all cases accounted for by a reduction in the probability of release of neurotransmitter, with no change in quantal size. Other EPSPs either showed negligible trial‐to‐trial amplitude fluctuation, or could not be resolved into quantal parameters without ambiguity. 5. By comparing the variance components of the EPSP peak amplitude distribution, the hypothesis was tested that the entire action of baclofen was to reduce quantal amplitude. This was rejected for sixteen out of thirty Ia and three out of five VQ EPSPs (P less than 0.05). 6. These results support a presynaptic site of action of baclofen on the terminals of Ia afferents, by decreasing the probability of release of neurotransmitter. They also indicate a similar, although weaker, action on VQ terminals. No evidence was found for an action on the postsynaptic membrane properties or synaptic conductance.
Effects of defolliculation on membrane current responses of Xenopus oocytes.
Authors: Miledi R , Woodward R M
Published: December 2014

1. Catecholamines, adenosine, gonadotrophins, vasoactive intestinal peptide (VIP) and E‐series prostaglandins all elicit K+ currents in follicle‐enclosed Xenopus oocytes. Evidence suggests that cyclic nucleotides act as intracellular messengers in the activation of this K+ conductance. Muscarinic agonists and some divalent cations (e.g. Co2+, Mn2+, Ni2+ and Cd2+) elicit slow oscillatory Cl‐ currents, which are activated through hydrolysis of inositol phospholipids and mobilization of intracellular calcium by inositol phosphates. 2. We investigated whether these membrane current responses were generated in the oocyte itself or in enveloping follicular cells which are coupled to the oocyte by gap junctions. Oocytes were defolliculated, either enzymatically using collagenase, or by manual dissection combined with rolling over poly‐L‐lysine‐coated slides. Removal of follicular cells was checked using scanning electron microscopy. Membrane current responses of defolliculated oocytes were compared with responses seen in follicle‐enclosed oocytes taken from the same ovary. 3. The K+ responses evoked by all the various hormones/neurotransmitters were either drastically reduced (greater than 90%) or abolished by defolliculation. K+ currents generated by the adenylate cyclase activator forskolin and by intraoocyte injection of adenosine 3',5'‐cyclic monophosphate (cyclic AMP), or guanosine 3',5'‐cyclic monophosphate were similarly reduced in defolliculated oocytes. In contrast, oscillatory Cl‐ currents to acetylcholine and divalent cations were selectively preserved through defolliculation. 4. Injection of cyclic AMP (1‐20 pmol) into defolliculated oocytes had little or no effect on oscillatory Cl‐ currents elicited by ACh. However, the calcium‐dependent transient Cl‐ current, activated by depolarization of the oocyte membrane, was consistently potentiated (100‐900%) by injections of cyclic AMP (1‐10 pmol). 5. These experiments suggest that cyclic nucleotide‐activated K+ currents arise essentially in follicular cells and are monitored within the oocyte through electrical coupling by gap junctions. Oscillatory Cl‐ responses evoked by ACh and divalent cations are produced largely or wholly in the oocyte itself.
Brain regions involved in the development of acute phase responses accompanying fever in rabbits.
Authors: Morimoto A , Murakami N , Nakamori T , Sakata Y , Watanabe T
Published: December 2014

1. The effects of microinjection of rabbit endogenous pyrogen and human recombinant interleukin‐1 alpha on rectal temperature and acute phase responses were extensively examined in forty different brain regions of rabbits. The acute phase responses that were investigated were the changes in plasma levels of iron, zinc and copper concentration and the changes in circulating leucocyte count. 2. The rostral hypothalamic regions, such as nucleus broca ventralis, preoptic area and anterior hypothalamic region, responded to the microinjection of endogenous pyrogen or interleukin‐1 by producing both fever and acute phase responses. 3. The microinjection of endogenous pyrogen or interleukin‐1 into the rostral hypothalamic regions significantly decreased the plasma levels of iron and zinc concentration 8 and 24 h after injection. The circulating leucocyte count increased 8 h after injection. However, neither the injections of endogenous pyrogen nor interleukin‐1 affected the number of red blood cells. 4. The present results show that the rostral hypothalamic regions respond directly to endogenous pyrogen or interleukin‐1 with the consequent development of fever and acute phase responses.
Epidural anaesthesia and cardiovascular responses to static exercise in man.
Authors: Mitchell J H , Reeves D R , Rogers H B , Secher N H
Published: December 2014

1. In human subjects, sustained static contractions of the knee extensors were performed in one leg with the same absolute (10% of the initial maximal voluntary contraction) and relative (30% of the maximal voluntary contraction immediately prior to the static exercise) intensities before and during epidural anaesthesia. Epidural anaesthesia reduced strength to 62 +/‐ 8% of the control value and partially blocked sensory input from the working muscles. During contractions performed with the same relative force, the increases in mean arterial pressure and heart rate were greater during control contractions than during epidural anaesthesia. During contractions at the same absolute force, there was no significant difference in magnitude of cardiovascular responses between control contractions and contractions performed during epidural anaesthesia. 2. The metabolic role in the exercise pressor reflex was assessed by applying an arterial leg cuff 10 s before cessation of exercise and through the following 3 min of recovery. Although mean arterial pressure and heart rate decreased immediately after cessation of exercise, application of the arterial occlusion cuff resulted in higher post‐exercise mean arterial pressure and heart rate values. Control and epidural mean arterial pressures during arterial occlusion were not significantly different. 3. The results of this study suggest that the reflex neural mechanism rather than the intended effort (central command) is important in determining the blood pressure and heart rate responses to static exercise in man. That is, when epidural anaesthesia diminishes sensory feedback and produces muscular weakness, central command does not determine the cardiovascular response. This conclusion, however, is opposite to that derived from experiments with partial neuromuscular blockade which demonstrated the importance of central command in determining the cardiovascular response to static exercise (Leonard, Mitchell, Mizuno, Rube, Saltin & Secher, 1985). Taken together, these two studies are complementary and support the concept that both central and reflex neural mechanisms play roles in regulating arterial blood pressure and heart rate during static exercise in man.
Ionic basis for the intrinsic activation of rat supraoptic neurones by hyperosmotic stimuli.
Authors: Bourque C W
Published: December 2014

1. Magnocellular neurosecretory cells (MNCs) were impaled in the supraoptic nucleus of rat hypothalamic explants maintained in vitro. Current‐ and voltage‐clamp analysis of the osmotically induced response was performed at 34 degrees C. 2. Addition of mannitol or NaCl to cause a rise in fluid osmolarity (greater than +6 mosM) caused a membrane depolarization whose amplitude increased when elicited from more hyperpolarized levels. Changes in temperature (34‐28 degrees C), addition of TTX, or superfusion with Na(+)‐free or Ca2(+)‐free solutions did not block the osmotically induced depolarization. In control solutions the response was consistently accompanied by an increase in the frequency of spontaneous postsynaptic potentials. Thus, osmotic stimuli have a direct effect on MNCs, and they also apparently activate other neurones which are presynaptic to these cells. 3. Under voltage‐clamp, hyperosmotic stimuli induced an inward current (Io) accompanied by an increase in membrane conductance. The current was unaffected or slightly enhanced by doubling the external K+ concentration. Io was also characterized by a linear I‐V relation (between ‐100 and ‐50mV) and an extrapolated reversal potential near ‐10 mV. Io presumably results from the activation of a voltage‐independent and non‐selective cationic conductance. 4. Hyperosmotic stimuli did not affect the depolarizing after‐current (IDAP) responsible for the production of phasic bursts. However, the inward shift of the post‐spike I‐V curve caused by Io could reduce or eliminate the region of net outward current which lies negative to spike threshold in silent neurones. Thus in MNCs displaying IDAP, activation of Io by a rise in osmotic pressure can induce or enhance phasic bursting activity. 5. Application of hyperosmotic stimuli sufficient to excite most MNCs (+20 to +80 mosM) did not elicit a response from any of seventeen neurones impaled in areas lateral and caudal to the supraoptic nucleus. Recordings obtained from three CA1 neurones in slices of rat hippocampus revealed that stimuli in excess of +100 mosM are required to evoke appreciable non‐specific depolarizations. 6. These studies indicate that the specific endogenous osmosensitivity of MNCs results from the activation of the intrinsic current Io. Furthermore, interactions between Io and IDAP explain how osmotic stimuli can lead to the induction of phasic bursting activity, a response which is known to potentiate the secretion of vasopressin from the neural lobe.
Effects of small changes in carotid sinus pressure on renal haemodynamics and function in dogs.
Authors: Karim F , Poucher S M , Summerill R A
Published: December 2014

1. In dogs anaesthetized with chloralose and artificially ventilated, the carotid sinuses were vascularly isolated and perfused with arterial blood. Mean aortic pressure was held constant at 111 +/‐ 2 mmHg (mean +/‐ S.E.M., n = 18) by means of a pressure bottle connected to the aorta and a Starling resistance. Both vagus nerves were sectioned in the neck and propranolol hydrochloride (1 mg kg‐1 h‐1) or atenolol (0.5‐4 mg kg‐1 h‐1) was administered. The left and right renal blood flows were measured by electromagnetic flowmeters (wrap‐round probes), glomerular filtration rate by creatinine clearance, urinary sodium by flame photometry and solute excretion by osmometry. 2. In six dogs decreasing pressure in the isolated carotid sinuses from 119 +/‐ 4 to 78 +/‐ 3 mmHg (n = 9) resulted in significant decreases in renal blood flow by 18 +/‐ 3% (P less than 0.01), glomerular filtration rate by 41 +/‐ 9% (P less than 0.01), filtration fraction by 30 +/‐ 11% (P less than 0.05), urine flow by 46 +/‐ 6% (P less than 0.001), sodium excretion by 46 +/‐ 9% (P less than 0.001) and osmolar excretion by 44 +/‐ 6% (P less than 0.001). Fractional sodium excretion did not change significantly. Increasing carotid sinus pressure back to 120 +/‐ 4 mmHg (n = 6) resulted in increases in all the variables to values not significantly different from those at initial high carotid pressure. 3. Ligation of left renal nerves at low carotid sinus pressure (83 +/‐ 3 mmHg, n = 5) caused significant increases in all of the variables in the left kidney. After ligation, changes in carotid sinus pressure produced no effect on the denervated left kidney, but in the three dogs in which the responses of the right kidney were also tested, the usual responses after denervation of the left kidney were seen. 4. The results show that changes in carotid sinus pressure around the normal range can result in significant reflex effects on renal haemodynamics and function and that these effects are mediated solely by renal sympathetic nerves. The influence of any extrarenal humoral factors seems to be minimal.
Differential modulation by pulmonary stretch afferents of some reflex cardioinhibitory responses in the cat.
Authors: Daly M B , Kirkman E
Published: December 2014

1. Cats were anaesthetized with a mixture of chloralose and urethane, and were artificially ventilated, the thorax being opened via a medial sternotomy. 2. Various cardiovascular receptors were stimulated during reflex inhibition of the central inspiratory neurones produced by electrical stimulation of both superior laryngeal nerves simultaneously, while the afferent input from the lungs was held constant by temporarily interrupting artificial respiration, the lungs being held static in their expiratory position. 3. Reflex cardioinhibitory responses were elicited by stimulation of (a) the carotid body chemoreceptors by intracarotid injections of cyanide; (b) the arterial baroreflex by controlled elevations of the blood pressure; (c) the carotid sinus baroreceptors by raising the pressure in isolated perfused carotid sinus preparations; (d) cardiac receptors by left atrial injections of veratridine, and (e) pulmonary C fibres (including J receptors) by right atrial injections of phenyl biguanide. 4. The effects of single inflations of the lungs on these reflex cardioinhibitory responses were studied and compared with the effects of the various inputs alone. 5. Stepwise increases in lung volume, while having no consistent effect on arterial blood pressure, progressively diminished the arterial chemoreceptor‐induced bradycardia to a value of about 7% of the control response without lung inflation. The pulmonary afferents were less effective on reflex responses from other inputs, the corresponding values being: arterial baroreflex, 66%; carotid baroreceptors, 66%, and cardiac receptors, 70%. These effects of lung inflation were abolished by selective denervation of the lungs. 6. In contrast, the size of the bradycardia evoked by pulmonary C fibre stimulation was, on average, unaffected by inflation of the lungs. In some tests the response was actually increased. 7. The differential modulation by lung inflation of these reflex cardioinhibitory responses were the same after upper thoracic sympathectomy indicating that pulmonary afferents and cardiac efferents involved fibres in the vagus nerves. 8. The possible central mechanisms responsible for the differential modulation by lung inflation of cardioinhibitory reflexes are discussed.
Stimulation of chloride secretion by N‐formyl‐methionylleucylphenylalanine (FMLP) in rabbit ileal mucosa.
Authors: Finley R B , Smith P L
Published: December 2014

1. Formyl‐methionyl peptides are potent neutrophil chemoattractants which may be involved in inflammatory responses in the intestine. Effects of formyl‐methionylleucylphenylalanine (FMLP) on electrical properties and Cl‐ fluxes were examined with the Ussing chamber technique employing stripped segments of rabbit ileal mucosa. 2. Serosal but not mucosal addition of FMLP elicited a transient (peak effect within 2 min), concentration‐dependent (maximal effect at 30 nM and half‐maximal effect at 3 nM) increase in short‐circuit current (Isc) which was not inhibited by pretreatment of the tissue with mepyramine (10 microM), tetrodotoxin (0.1 microM) or atropine (10 microM). The related peptides FMLP‐benzylamide (FMLP‐benz) and methionyl‐leucylphenylalanine (MLP) produced concentration‐dependent increases in Isc which were qualitatively similar to FMLP. The order of potencies of these peptides was FMLP‐benz greater than FMLP greater than MLP. 3. The lack of an effect of mucosal FMLP (300 nM) on Isc does not appear to be due to metabolism since addition of an aliquot of this bathing solution to the serosal bathing solution of a naive tissue increased Isc as expected. Addition of FMLP (30 nM) to the serosal bathing solution of a tissue pre‐stimulated with serosal FMLP (30 nM) failed to elicit a response. 4. The increase in Isc produced by FMLP (30 nM) was inhibited by removal of Ca2+ from the serosal bathing solution and by removal of Cl‐ from both bathing solutions. FMLP (30 nM) increased the serosal‐to‐mucosal flux of Cl‐ and decreased the transepithelial conductance (Gt). 5. The cyclo‐oxygenase inhibitors indomethacin (1 microM), mefenamate (10 microM) or piroxicam (30 microM) added to both the serosal and mucosal bathing solutions inhibited the increase in Isc elicited by FMLP (30 nM). 6. Measurement of release of immunoreactive thromboxane B2, 6‐keto‐PGF1 alpha and PGE2 revealed that FMLP (30 nM) selectively increased PGE2 release by an indomethacin‐sensitive pathway. 7. Thus, in addition to being potent chemoattractants, formyl‐methionyl peptides stimulate electrogenic Cl‐ secretion and also increase prostaglandin production.
Intracellular Ca2+ transients during rapid cooling contractures in guinea‐pig ventricular myocytes.
Authors: Bers D M , Bridge J H , Spitzer K W
Published: December 2014

1. We measured intracellular Ca2+ transients during rapid cooling contractures (RCCs) in guinea‐pig ventricular myocytes using the fluorescent Ca2+ indicator, Indo‐1. 2. Rapid cooling of myocytes from 22 to 0‐1 degrees C induced a rapid increase in [Ca2+]i which preceded the peak of the contraction and was sometimes large enough to saturate Indo‐1. This indicates that [Ca2+]i may reach greater than 10 microM during an RCC. 3. The [Ca2+]i during the RCC slowly declined from its peak value and most of this decline in [Ca2+]i can be attributed to slow reaccumulation of Ca2+ by the sarcoplasmic reticulum (SR) in the cold. RCCs induced in the absence of Cao2+, were not different from control, supporting previous conclusions that RCCs depend exclusively on intracellular Ca2+ stores. 4. RCCs are depressed by long rest periods (rest decay) or by exposure to ryanodine or caffeine, which supports conclusions that RCCs are due to Ca2+ release from the SR. The rest decay of RCCs can be almost completely prevented by applying Nao(+)‐free solution during the rest period. This implies that the loss of SR Ca2+ during rest depends on the sarcolemmal Na(+)‐Ca2+ exchange (and not the sarcolemmal Ca2(+)‐ATPase pump). 5. Rapid rewarming during an RCC normally leads to an additional transient contraction (or rewarming spike), without any increase in [Ca2+]i. Thus, the rewarming spike might be attributable to an increase in myofilament Ca2+ sensitivity induced by rewarming. 6. A second RCC is used to assess the fraction of Ca2+ which is re‐sequestered by the SR during relaxation from the first RCC. In control solution progressive RCCs decline in amplitude, but in Na(+)‐free, Ca2(+)‐free solution they are of constant amplitude. We conclude that the SR Ca2+ pump and Na(+)‐Ca2+ exchange are responsible for relaxation and that the latter may account for 20‐50% of relaxation. 7. These results support the use of RCCs as a useful means of assessing SR Ca2+ content in intact cardiac muscle cells.
Cross‐bridge movement in rat cardiac muscle as a function of calcium concentration.
Authors: Matsubara I , Maughan D W , Saeki Y , Yagi N
Published: December 2014

1. By applying the X‐ray diffraction method to chemically skinned papillary muscles of the rat, the transfer of myosin heads from the thick to the thin filaments was studied as a function of Ca2+ concentration. 2. No significant transfer of the heads occurred when the Ca2+ concentration was below the threshold of contraction (pCa 6.2). 3. During the maximum isometric contraction at pCa 4.4, 80% of the myosin heads were transferred to the thin filament. 4. When the muscle was activated isometrically at low Ca2+ concentrations (pCa 6.2‐5.8), where the average tension was less than 20% of the maximum, a disproportionately large number of myosin heads were transferred to the thin filament. 5. It was concluded that a significant fraction of the heads transferred at the low Ca2+ concentrations does not produce tension.
Characterization of inhibition mediated by adenosine in the hippocampus of the rat in vitro.
Authors: Gerber U , Greene R W , Haas H L , Stevens D R
Published: December 2014

1. Intracellular recordings with single‐electrode voltage clamp were employed to study the mechanism of adenosine‐elicited inhibition of CA1 neurones of the rat in vitro. 2. Adenosine elicits a steady‐state outward current in association with an increase in conductance. The driving force varied with external potassium concentration as predicted by the Nernst equation for a change primarily in potassium permeability. 3. Adenosine current was blocked by high concentrations of 4‐aminopyridine or barium. In the majority of neurones this current was voltage insensitive. In the remainder, the current was inwardly rectifying. The rectification was blocked by tetraethylammonium. 4. When the adenosine‐elicited potassium current was blocked, slow inward currents, normally carried by calcium, were unaffected by adenosine. We conclude that this adenosine inhibition is mediated by an increase in a voltage‐ and calcium‐insensitive potassium conductance in CA1 neurones.
Effect of intracellular and extracellular pH on contraction in isolated, mammalian cardiac muscle.
Authors: Bountra C , Vaughan‐Jones R D
Published: December 2014

1. Intracellular pH (pHi) and Na+ activity were recorded (ion‐selective microelectrodes) in guinea‐pig papillary muscle and the sheep cardiac Purkinje fibre while simultaneously recording twitch tension. The effects of intracellular acidosis and alkalosis upon contraction were investigated. 2. A fall of pHi produced by reducing pHo was associated with a fall of twitch tension. Similarly, a rise of pHi produced by raising pHo produced a rise of twitch tension. The time course of the changes in tension correlated with the time course of changes of pHi rather than pHo. These results are consistent with previous work showing that acidosis inhibits contraction and that the inhibition depends upon a fall of pHi. 3. Changes of pHi were produced while maintaining pHo constant at 7.4. Removal of NH4Cl or addition of sodium acetate (pHo 7.4) reduced pHi but this gave either an increase of tension (papillary muscle) or an initial fall followed by a subsequent recovery of tension (Purkinje fibre). The increase or recovery of tension occurred despite the fact that there was an intracellular acid load. Thus, reducing pHi at constant pHo can increase tension whereas reducing pHi at low pHo (6.4, see paragraph 2) inhibits tension. 4. The increase of recovery of tension during intracellular acidosis produced at a constant pHo (7.4) was associated with a rise of intracellular sodium activity (aiNa). Amiloride (1.5 mmol/l), an inhibitor of Na(+)‐H+ exchange, prevented the rise of aiNa during intracellular acidosis and also prevented the recovery of tension. It is concluded that the increase or recovery of tension at low pHi is secondary to a rise of aiNa caused by stimulation of Na(+)‐H+ exchange. A rise of aiNa will elevate Ca2+ via sarcolemmal Na(+)‐Ca2+ exchange and thus will elevate tension. 5. An intracellular acidosis produced by reducing pHo (6.4) does not elevate aiNa in the Purkinje fibre. In papillary muscle, aiNa rises but this occurs slowly and the rise is 50% smaller than that seen when the same intracellular acidosis is induced at normal pHo (7.4). The net depression of tension under these conditions thus correlates with the lack of a large rise of aiNa. 6. Knowing the quantitative dependence of tension upon both aiNa and pHi in the two tissues it is possible to predict the recovery of twitch tension during intracellular acidosis at constant pHo (7.4), using the changes of pHi and aiNa measured under these conditions.(ABSTRACT TRUNCATED AT 400 WORDS)
The probability of quantal secretion at release sites of different length in toad (Bufo marinus) muscle.
Authors: Bennett M R , Lavidis N A , Lavidis‐Armson F
Published: December 2014

1. The evoked quantal secretion recorded with an extracellular microelectrode (me) at selected sites along motor terminal branches visualized with the fluorescent dye 3‐3 diethyloxardicarbocyanine iodide (DiOC2(5)) was compared with the maximum length of the synaptic contact at these release sites reconstructed from serial sections examined with the electron microscope. In addition the relationship between the binomial probability of secretion at release sites (pe) and the length of the synaptic contact was determined in an extracellular calcium. [Ca2+]o, of 0.35 mM. 2. Three of the six terminal branches studied in this way showed a decline in synaptic contact length of release sites from near the point of nerve entry (proximal) to the end of the branch (distal). The remaining three branches showed an increase in synaptic contact length near their middle, and in each case this was associated with a Schwann cell nucleus: contact length then declined to the end of the branches. 3. Both me and pe increased linearly with an increase in the maximum length of the synaptic contact over a range from 0.4 to 4.0 microns. This occurred independently of how the synaptic contact length varied along the length of terminal branches. The value of pe increased by about 0.05 for each 1 micron increase in synaptic contact length in a [Ca2+]o of 0.35 mM. 4. The decrease in synaptic contact length along the proximal parts of terminal branches, in which this occurs, is mostly due to a decrease in the length of close opposition (less than 0.2 micron) between the nerve terminal membrane and the postsynaptic membrane: the decrease in more distal parts of branches is due to the progressive encroachment of Schwann cell processes between the presynaptic and postsynaptic membranes as well as a decrease in synaptic contact length.
Two components of potassium current activated by depolarization of single smooth muscle cells from the rabbit portal vein.
Authors: Beech D J , Bolton T B
Published: December 2014

1. Using the patch‐clamp technique at 20‐23 degrees C membrane currents were recorded from single smooth muscle cells enzymatically isolated from the rabbit portal vein. Single‐channel currents were observed in outside‐out patches excised from these. 2. Outward current elicited upon depolarization from ‐70 mV was not activated as a result of Ca2+ influx. It could be divided into two components: an inactivating, 4‐aminopyridine‐ and phencyclidine‐sensitive low‐noise current (IdK), and a non‐inactivating, tetraethylammonium (TEA)‐ and charybdotoxin‐sensitive high‐noise current (IcK). 3. IdK activated with a threshold around ‐40 mV and was carried by K+. It was substantially inhibited by 4‐aminopyridine (5 mM) or phencyclidine (0.1 mM) but was insensitive to TEA+ (4 mM), charybdotoxin (0.1 microM) or apamin (0.1 microM). Upon stepping to 0 mV it reached a maximum within about 0.2 s. The time course of its activation could be described by a fourth‐order single exponential; the time constants of these exponentials changed e‐fold every 56 mV. It inactivated in a time‐ and voltage‐dependent manner with a fast and slow component, and was about 50% available at ‐30 mV. From single‐channel recordings in isolated patches single channels underlying this current have a small unitary conductance (around 5 pS). 4. IcK did not inactivate significantly over 6 s. It activated with a less negative threshold than IdK, usually near 0 mV when the pipette solution contained 0.8 mM‐EGTA with no added calcium. It was blocked by TEA (4 mM) or charybdotoxin (0.1 microM), but not by 4‐aminopyridine (5 mM), phencyclidine (0.1 mM) or apamin (0.1 microM). Estimates of the single‐channel conductance from the noise variance of the whole‐cell current IcK indicated a value at +80 mV of 115 pS, very similar to that of the large‐conductance Ca2(+)‐activated K+ channels studied in these cells using single‐channel recording. 5. The results suggest that outward current evoked by depolarization from the resting potential can be carried by 100 pS Ca2(+)‐activated K+ channels and by small‐conductance delayed‐rectifier K+ channels. It is likely that opening of both types of channel contributes to the repolarization phase of the action potential in this smooth muscle.
Changes in force and intracellular metabolites during fatigue of human skeletal muscle.
Authors: Cady E B , Jones D A , Lynn J , Newham D J
Published: December 2014

1. The relationship between intracellular metabolites and the generation of force during fatigue has been examined in the first dorsal interosseous muscle of the hand. With the arm made ischaemic, the muscle was fatigued by three bouts of maximal voluntary contraction, leaving approximately three minutes ischaemic rest between contractions. During one series of experiments intracellular phosphorus metabolites were measured by nuclear magnetic resonance during the intervals between the fatiguing contractions: in the second series contractile properties were tested with brief electrical stimulation during the rest intervals. 2. The relationships between loss of force and change in metabolite concentrations obtained with four normal subjects were compared with those from one subject with myophosphorylase deficiency (MPD) who could not utilize muscle glycogen and therefore produced no hydrogen ion from glycolysis during exercise. 3. For both the MPD and normal subjects the relationship between relative force loss and inorganic phosphate (Pi) concentration was curvilinear, force changing little in the early stages of the contraction when the intracellular Pi was accumulating rapidly but falling faster when the Pi was above 25 mM and increasing relatively slowly. 4. In the normal subjects intracellular pH fell from a mean of 7.03 +/‐ 0.01 (mean +/‐ S.E. of mean, n = 19) in the fresh muscle to 6.51 +/‐ 0.02 at the end of the fatiguing exercise; force, as a percentage of the initial value, fell in proportion to the increase in H+ concentration. In the MPD subject pH did not change and force loss was therefore independent of H+ accumulation. In the normal subjects the force of the fatiguing muscle showed an approximately linear relationship with the concentration of the monobasic form of inorganic phosphate. However, the MPD subject showed a quite different relationship, with force loss being much greater for a given concentration of monobasic phosphate. This result indicates that monobasic phosphate is not a unique determinant of force loss in fatigued muscle. 5. During the first 60 s of recovery in the normal subjects, pH remained low while force recovered, indicating a mechanism of force loss that was independent of H+ accumulation. However, the recovery of force was not complete, so that for comparable phosphocreatine contents the recovering, more acid, muscle generated less force than the muscle that was being fatigued. It was estimated that H(+)‐dependent and independent mechanisms contributed roughly equally to the observed force loss. The relationship between force and the concentration of monobasic phosphate differed in fatiguing and recovering muscle.
Excitatory amino acid‐receptor‐mediated EPSPs in rat dorsolateral septal nucleus neurones in vitro.
Authors: Gallagher J P , Hasuo H
Published: December 2014

1. Intracellular recordings were made from rat dorsolateral septal nucleus (DLSN) neurones in vitro. We investigated depolarizations resulting from pressure application of excitatory amino acids and compared these to synaptically evoked excitatory postsynaptic potentials (EPSPs). 2. EPSPs evoked by focal fimbrial afferent stimulation in saline with 30‐50 microM‐bicuculline and 1.2 mM‐Mg2+ yielded a linear amplitude‐voltage relationship: their reversal potential was ‐3 mV. These EPSPs exhibited little sensitivity to 2‐amino‐5‐phosphonopentanoate (APV), an N‐methyl‐D‐aspartate(NMDA)‐receptor‐specific antagonist, but were markedly depressed by kynurenic acid, a broad‐spectrum excitatory amino acid antagonist. 3. In Mg2(+)‐free solution, the amplitude and the duration of EPSPs were increased markedly masking the following inhibitory postsynaptic potential (IPSP) and the late hyperpolarizing potential (LHP). These facilitated and broadened EPSPs were sensitive to APV or Mg2+. The APV or Mg2(+)‐sensitive component of the EPSP obtained by digital subtraction suggests a slower time course for the NMDA‐receptor‐mediated EPSP compared to the non‐NMDA‐receptor‐mediated EPSP. On the other hand, in normal Mg2+ solution an EPSP evoked by either a single strong stimulus or by repetitive stimuli had APV‐sensitive components. 4. The depolarizing potentials induced by pressure application of glutamate, kainate, alpha‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionate (AMPA), quisqualate or NMDA were compared. The amplitude‐voltage relationship of depolarizations induced by NMDA obtained in a normal Mg2+ solution was non‐linear, but approached linearity when the same responses were recorded in a Mg2(+)‐free solution. Depolarizations induced by kainate, AMPA and quisqualate were linear in their amplitude‐voltage relationship in the presence or absence of Mg2+. APV blocked NMDA‐induced depolarizations specifically, while kynurenic acid blocked all the depolarizations induced by NMDA, quisqualate, or kainate. 5. Our data demonstrate the existence of NMDA‐receptor‐mediated synaptic potentials in the rat DLSN, the characteristics of which are similar to those in other central nervous system regions.
Transient and persistent sodium currents in normal and denervated mammalian skeletal muscle.
Authors: Gage P W , Lamb G D , Wakefield B T
Published: December 2014

1. Transient and persistent tetrodotoxin‐sensitive sodium currents were recorded in response to depolarizing voltage pulses in voltage clamped segments of rat extensor digitorum longus muscle fibres at 20‐25 degrees C in a triple Vaseline gap. 2. Appreciable persistent sodium current but little or no transient current was seen in response to depolarizations of up to 15 mV from a holding potential of ‐100 mV. 3. The maximum amplitude of both transient and persistent sodium currents occurred with depolarizations to ‐40 mV: the average peak amplitude of the transient current in fibres with a holding potential of ‐90 mV was ‐0.22 +/‐ 0.03 mA/microF (mean +/‐ 1 S.E.M., seven fibres) and the average amplitude of the persistent current was ‐0.94 +/‐ 0.10 microA/microF (mean +/‐ 1 S.E.M., twelve fibres). With a holding potential of ‐100 mV, the average amplitudes of the transient and persistent currents were ‐0.46 +/‐ 0.10 mA/microF (four fibres) and ‐1.4 +/‐ 0.22 microA/microF (five fibres), respectively. 4. The average maximum persistent sodium conductance in seven fibres held at ‐90 mV was 0.13 +/‐ 0.0078 microS and the potential for half‐maximum conductance was ‐53 +/‐ 0.74 mV (mean +/‐ 1 S.E.M.). 5. When the transient sodium current was completely inactivated with 100 ms conditioning depolarizations to potentials more positive than ‐50 to ‐60 mV, there was little inactivation of the persistent current. 6. In six denervated fibres, the average amplitudes of the transient and persistent sodium currents generated by pulses to ‐40 mV from a holding potential of ‐90 mV were ‐0.11 +/‐ 0.01 mA/microF and ‐0.88 +/‐ 0.12 microA/microF, respectively (mean +/‐ 1 S.E.M.). It was concluded that there was a decrease in transient current but not persistent current amplitude following denervation and that the persistent current in denervated fibres with an increased input resistance could give rise to the spontaneous action potentials responsible for fibrillation.
Role of central opiate receptor subtypes in the circulatory responses of awake rabbits to graded caval occlusions.
Authors: Evans R G , Ludbrook J , Van Leeuwen A F
Published: December 2014

1. In unanaesthetized rabbits, haemorrhage was simulated by inflating a cuff placed round the inferior vena cava so that cardiac output fell at a constant rate of approximately 8% of its resting value per minute. The circulatory responses were measured after injections into the fourth ventricle of saline vehicle, selective opioid antagonists, selective opioid agonists, and agonist‐antagonist mixtures. Three sets of experiments were done to determine if a specific subtype of opiate receptor within the central nervous system is responsible for the circulatory decompensation that occurs during simulated haemorrhage. 2. In six rabbits the effects of ascending doses of the antagonists naloxone (mu‐selective), Mr 2266 (kappa‐ and mu‐selective), ICI 174864 (delta‐selective) and nor‐binaltorphimine (kappa‐selective) were tested. In three rabbits the effects of the antagonist naloxone, the agonists HTyr‐D‐Ala‐Gly‐MePhe‐NH(CH2)2OH (DAGO, mu‐selective), U 50488H (kappa‐selective), and [D‐Pen2,D‐Pen5]‐enkephalin (DPDPE, delta‐selective), and combinations of these agonists with naloxone were tested. In four rabbits the dose‐related effects of DAGO on respiratory, as well as circulatory, functions were examined. 3. After injecting saline vehicle, the circulatory response to simulated haemorrhage had two phases. During the first phase, systemic vascular conductance fell, heart rate rose, and mean arterial pressure fell by only approximately 10 mmHg. A second, decompensatory, phase began when cardiac output had fallen to approximately 50% of its resting level. At this point, there was an abrupt rise in systemic vascular conductance and a fall in mean arterial pressure to less than or equal to 40 mmHg. 4. The lower range of doses of naloxone (3‐30 nmol), Mr 2266 (10‐100 nmol), ICI 174864 (10‐30 nmol), and all doses of nor‐binaltorphimine (1‐100 nmol), were without effect on the circulatory response to stimulated haemorrhage. Higher doses of naloxone (30‐100 nmol), Mr 2266 (100‐300 nmol) and ICI 174864 (30‐100 nmol) abolished the decompensatory phase. The relative order of antagonist potency was ICI 174864 greater than or equal to naloxone greater than Mr 2266 greater than or equal to nor‐binaltorphimine. 5. In the second set of experiments, the critical dose of naloxone necessary to prevent circulatory decompensation during simulated haemorrhage was 30‐150 nmol. The delta‐agonist DPDPE (50 nmol) did not affect the haemodynamic response to simulated haemorrhage, but it did block the effect of naloxone on the response.(ABSTRACT TRUNCATED AT 400 WORDS)
Participation of the kallikrein‐kinin‐receptor system in reflexes arising from neural afferents in the dog epicardium.
Authors: Staszewska‐Woolley J , Woolley G
Published: December 2014

1. Reflexogenic effects of bradykinin, lysyl‐bradykinin and endogenously formed kinins on neural afferents of the left ventricular epicardium were studied in anaesthetized, open‐chest dogs. 2. Epicardial application of either bradykinin (0.01‐10 micrograms), lysyl‐bradykinin (0.01‐10 micrograms) or tissue kallikrein (0.003‐1 U) consistently resulted in dose‐related increases in blood pressure and heart rate. The pressor and heart rate responses to epicardial kallikrein were slower in onset and longer lasting than those evoked by bradykinin or lysyl‐bradykinin. The effects of kallikrein, but not those of exogenous kinins, were subject to tachyphylaxis. The application of higher doses of kallikrein (0.1 or 1 U) also resulted in long‐lasting desensitization of the epicardium to the effects of bradykinin. 3. Treatment of the epicardium with a proteinase inhibitor, aprotinin, prevented the reflexogenic effects of kallikrein but not those of bradykinin or lysyl‐bradykinin. Treatment with aprotinin also counteracted post‐kallikrein desensitization of sensory receptors of the ventricular epicardium to the reflexogenic effect of bradykinin. 4. Superfusion of the epicardium with a selective B2 receptor antagonist, D‐Arg[Hyp3,Thi5,8,D‐Phe7]‐bradykinin, was equally effective in antagonizing the reflexogenic effects of kallikrein, bradykinin and lysyl‐bradykinin. 5. We conclude that the response to epicardial application of kallikrein indicates an ample presence of endogenous substrate for local formation of bradykinin and/or related kinins. These then initiate reflex activation of the cardiovascular system by interacting with specific B2 receptors associated with sympathetic afferent neurones in the dog epicardium. We suggest that the kallikrein‐kinin‐receptor system has a role in the reflex function of the cardiac sympathetic afferents in both physiological and pathological conditions.
Lymph flow in sheep limbs during local exposure to subatmospheric pressure.
Authors: Pippard C J , Roddie I C
Published: December 2014

1. Lymph flow and pressure were measured via cannulae inserted into afferent lymphatics draining the feet of anaesthetized sheep. 2. When the cannula outlet was at limb level, local exposure of the limb to graded decreases in ambient pressure caused graded increases in lymph flow with pressure values down to ‐50 mmHg. 3. When the cannula outlet was lowered below limb level to offset the negative pressure gradient imposed on the lymphatic vessels by suction, lymph flow rose progressively with decreasing ambient pressure values down to ‐70 mmHg. 4. When negative pressure gradients were imposed on the lymphatic vessels by raising the lymphatic cannula outlet in progressive steps above limb level, the vessels were able to expel lymph against gradients of up to 50 mmHg but lymph flow was greatly reduced against a gradient of 70 mmHg. 5. The results suggest that subatmospheric pressure may affect local lymph flow in two ways. By increasing blood capillary transmural pressure it may increase lymph flow by increasing tissue fluid formation. By imposing a negative pressure gradient along the lymphatics it may decrease lymph flow, especially at the most negative pressures, and the lymph flow response to subatmospheric pressure may be the algebraic sum of both effects.
Effects of 2‐amino‐4‐phosphonobutyric acid on responsivity and spatial summation of X cells in the cat retina.
Authors: Chen E P , Linsenmeier R A
Published: December 2014

1. We studied the effect of locally applied 2‐amino‐4‐phosphonobutyric acid (APB) on the response of X‐type cat retinal ganglion cells to stimulation by sinusoidal gratings of photopic mean luminance. 2. Application of APB produced a decrease in the mean firing rate of on‐centre X cells, but an increase in the mean firing rate of off‐centre X cells. 3. The response and responsivity of both on‐ and off‐centre X cells to drifting sinusoidal gratings were suppressed by APB. Under control conditions, the response amplitude was linear with grating contrast for contrasts less than 10%. During APB application, the slope of the contrast response curve was reduced, and linearity was maintained for a larger range of contrast. 4. Assuming that APB acts selectively on the cone to depolarizing bipolar cell synapse, the suppression of the response of on‐ and off‐centre X cells suggests a functional link between depolarizing bipolar cells and both types of X cell. 5. Because APB reduces the centre response of both on‐ and off‐centre X cells, caution should be observed in interpreting the effect of APB on higher visual centres in terms of the blockage of ‘on’ signals leaving the retina. 6. By analysing the spatial frequency tuning curve before and during APB application in terms of the difference‐of‐Gaussians model of receptive field structure, it was found that the balance between the integrated strengths of the centre and surround was not modified by APB. APB, however, had a differential effect on the summating area of the centre and surround. While the centre radius was unaffected by APB, the surround radius was reduced. This suggests that the peak sensitivity of the surround mechanism was reduced less severely than the peak sensitivity of the centre mechanism. 7. Strychnine also suppressed the response of the centre mechanism of both on‐ and off‐centre X cells to drifting gratings.