bluuebunny/crossref_metadata_2025 huggingface dataset:
Synaptic‐ and agonist‐induced excitatory currents of Purkinje cells in rat cerebellar slices.
Authors: Llano I , Marty A , Armstrong C M , Konnerth A
Published: December 2014

1. Postsynaptic currents originating from activation of the two major excitatory inputs to Purkinje cells were studied in thin slices of rat cerebellum, using the tight‐seal whole‐cell recording technique. Two types of excitatory postsynaptic currents were analysed: those evoked by stimulation of the granule cell‐parallel fibre system (PF‐EPSC) and those elicited by stimulation of the climbing fibres (CF‐EPSC). 2. Both types of postsynaptic currents had a linear current‐voltage relation, reversing at membrane potentials close to 0 mV. Their time course of activation was independent of the membrane potential. 3. For both types of postsynaptic currents, the time course of decay was well described by a single exponential function, with a time constant which increased as the membrane potential was made more positive. 4. Postsynaptic currents arising from stimulation of the climbing fibre generally had a slightly faster time course of onset and decay than those associated with stimulation of the granule cell‐parallel fibre system. The average values of the 10‐90% rise time were 1.8 +/‐ 0.4 ms (means +/‐ S.D., n = 7) for PF‐EPSCs and 0.8 +/‐ 0.3 ms (n = 9) for CF‐EPSCs. Time constants of decay, at a holding potential of ‐60 mV, had values of 8.3 +/‐ 1.6 ms (n = 7) and 6.4 +/‐ 1.1 ms (n = 9) for PF‐EPSCs and CF‐EPSCs respectively. 5. CF‐EPSCs and PF‐EPSCs had the characteristics described above in slices derived from animals aged 9‐22 days old and 9‐15 days old, respectively. The PF‐EPSCs in animals older than 15 days had very slow time courses and positive apparent reversal potentials, suggesting that they originated from distal locations, not under accurate voltage control. 6. In order to assess the quality of the voltage clamp, responses to hyperpolarizing pulses from ‐70 mV were analysed. The capacitive currents could be fitted by the sum of two exponentials, and were interpreted with an equivalent electrical circuit comprising two main compartments (soma and proximal dendrites on one hand, distal dendrites on the other). Analysis of synaptic currents in terms of this model suggested that the recorded time course of decay was approximately correct. 7. CF‐EPSCs as well as PF‐EPSCs were insensitive to the NMDA receptor antagonist 3‐3(2‐carboxypiperazine‐4‐yl)propyl‐1‐phosphonate (CPP), but were blocked in a dose‐dependent reversible manner by the non‐NMDA antagonist 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX).(ABSTRACT TRUNCATED AT 400 WORDS)
Non‐thermal vasodilatation by radio frequency burst‐type electromagnetic field radiation in the frog.
Authors: Miura M , Okada J
Published: December 2014

1. When the web of the anaesthetized Xenopus laevis was perfused with Ringer solution maintained at 20 degrees C, radio frequency (RF) burst‐type electromagnetic (EM) field radiation not only dilated arterioles of the web which had been preconstricted with noradrenaline, but also dilated arterioles under non‐stimulated conditions. The EM field‐induced vasodilatation increased slowly and reached a plateau 60 min after the onset of radiation. After the cessation of radiation, vasodilatation remained for 10‐20 min, then slowly subsided. 2. When a 10 MHz, 1 V (peak to peak) generator voltage induced a 7.3 milliGauss, 2.19 V cm‐1 EM field, the vasodilatory effect was optimum when bursts were applied 50% of the total time at 10 kHz burst rate. 3. The vasodilatory effect was not secondary to dielectric heat in the web, because the EM field was too weak to have produced enough heat to dilate the arterioles and heat would have been constantly conducted away by the perfusion solution. 4. During perfusion with Ringer solution warmed to 30 degrees C, no vasodilatation was found, but perfusion with Ringer solution warmed to 35 degrees C induced only 11% vasodilatation. Perfusion with Ringer solution warmed to 37 degrees C induced irreversible vasoconstriction. The pattern of vasodilatation induced by warm Ringer solution was different from the vasodilatory effect of weak EM field radiation. 5. The extent of the vasodilatory effect was influenced by Ca2+ concentration of the perfusion medium. Under normal Ca2+ conditions arterioles dilated to 126% of the control diameter, while under Ca(2+)‐free conditions arterioles dilated to 131% of the control value and under high‐Ca2+ conditions (twice the normal level) arterioles dilated to 111% of the control value. This suggests that the vasodilatory effect may be caused by facilitation of Ca2+ outflow, and the extent of this flow may settle down to the equilibrium level of countercurrent flux between Ca2+ influx and outflow. 6. The vasodilatory effect was not inhibited under perfusion with Na(+)‐free Ringer solution, suggesting that Na(+)‐Ca2+ exchange system may not be involved in the vasodilatory effect. The vasodilatory effect was inhibited by vanadate, an inhibitor of Ca(2+)‐ATPase, and was abolished by Methylene Blue, an inhibitor of guanylate cyclase. The evidence suggests that the mechanism of the vasodilatory effect may depend on an increase in Ca2+ outflow through the plasma membrane of the smooth muscle and/or an increase in Ca2+ influx into the sarcoplasmic reticulum.(ABSTRACT TRUNCATED AT 400 WORDS)
Kinetic properties of the glycine receptor main‐ and sub‐conductance states of mouse spinal cord neurones in culture.
Authors: Twyman R E , Macdonald R L
Published: December 2014

1. The kinetic properties of the two most frequent conductance states of glycine receptor channels from somata of mouse spinal cord neurones in cell culture were investigated using the outside‐out patch clamp technique. At low concentrations of glycine (0.5, 1 and 2 microM), single‐channel currents were recorded with two predominant amplitudes corresponding to a dominant or main‐conductance state of about 42 pS and a sub‐conductance state of about 27 pS. Both conductance states opened singly and in bursts of several openings. Total current evoked and single‐channel opening frequency increased as glycine concentration was increased from 0.5 to 2 microM. 2. For both conductance states mean open times were increased and open time frequency histograms were shifted to longer times as glycine concentration was increased from 0.5 to 2 microM. For both conductance states, three exponential components were required to fit best open time frequency distribution histograms at all glycine concentrations (0.5, 1 and 2 microM). The time constants of the exponential components for each conductance state were not significantly different across concentration, suggesting that the main‐ and sub‐conductance states of the channel each opened into at least three open states. For the main‐conductance state, the time constants were 1.09 +/‐ 0.09, 4.06 +/‐ 0.26 and 9.79 +/‐ 0.30 ms. For the sub‐conductance state, the time constants were 0.55 +/‐ 0.04, 2.64 +/‐ 0.35 and 8.57 +/‐ 1.08 ms. The increase in long open times with concentration was due primarily to a shift in relative frequency of occurrence of openings from the shortest to the two longest open states. 3. Closed time frequency distributions of closures between main‐conductance state openings, closures between sub‐conductance state openings and closures between both main‐ and sub‐conductance state openings were fitted with multiple exponential components, suggesting that the channel had several closed states. The two shortest time constants (0.16 +/‐ 0.01 and 1.26 +/‐ 0.13 ms) did not vary significantly with concentration (0.5‐2 microM) or method of analysis. The longer time constant varied with concentration. 4. Bursts were defined as groups of openings surrounded by closures greater than a critical closed time. For both conductances states, mean burst durations were increased and burst duration frequency histograms were shifted to longer times as glycine concentration was increased from 0.5 to 2 miroM. Burst duration frequency histograms contained four exponential components for the main‐conductance state and three exponential components for the sub‐conductance state.(ABSTRACT TRUNCATED AT 400 WORDS)
Afferent pathway(s) for pharyngeal dilator reflex to negative pressure in man: a study using upper airway anaesthesia.
Authors: Horner R L , Innes J A , Holden H B , Guz A
Published: December 2014

1. To determine the afferent pathways mediating pharyngeal dilator muscle activation in response to negative airway pressure in man, we recorded genioglossus electromyogram (EMG) activity (via intra‐oral bipolar surface electrodes) in response to 500 ms duration pressure stimuli of ‐15 and ‐25 cm H2O in normal, conscious, supine subjects relaxed at end‐expiration; responses were compared before and after upper airway anaesthesia. 2. Six rectified and integrated EMG responses were bin averaged for pressure stimuli applied with the glottis open (GO) and closed (GC) and to the outside of the face only (controls). Response magnitude was quantified as the ratio of the EMG activity for an 80 ms post‐stimulus period (before the subject's reaction time for tongue protrusion) to an 80 ms pre‐stimulus period. 3. In eight subjects, upper airway anaesthesia reduced the EMG responses with GC to a level indistinguishable from controls. After anaesthesia, responses with GO remained higher than those with GC. 4. With GC, the mean EMG responses decreased by 43% after selective anaesthesia of the nasal mucosa (trigeminal nerves) in two subjects, 32% after selective anaesthesia of the laryngeal mucosa (superior laryngeal nerves) in six subjects and by 21% after selective anaesthesia of the oropharyngeal mucosa (glossopharyngeal and lingual nerves) in four subjects. 5. We conclude that upper airway afferents mediate pharyngeal dilator muscle activation in response to negative pressure with GC and that subglottal receptors caused the increased activation with GO. With GC, the trigeminal and superior laryngeal nerves mediate an important component of the responses with the glossopharyngeal nerves playing a less important role.
Incorporation of chelator into guinea‐pig rods shows that calcium mediates mammalian photoreceptor light adaptation.
Authors: Matthews H R
Published: December 2014

1. The effects of steady light on the sensitivity and kinetics of the photocurrent response were studied in the rod photoreceptors of the guinea‐pig, using suction pipette recordings of circulating current. 2. The sensitivity of the flash response decreased with increasing background intensity according to Weber's law. Ultimately for the brightest backgrounds saturation ensued. The recovery phase of the flash response was accelerated by steady light, while the early rising phase was little affected. 3. These results indicate that guinea‐pig rods adapt to light in much the same way as do the rods and cones of lower vertebrates. 4. The role of cytoplasmic calcium concentration in this adaptation was studied by incorporation of the calcium chelator bis(o‐aminophenoxy)ethane‐ N,N,N',N'‐tetraacetic acid (BAPTA) into the rod cytoplasm. Superfusion with a solution containing the membrane‐permeant acetoxymethyl ester resulted in progressive changes in the response to light. 5. BAPTA incorporation retarded the falling phase of the flash response, thereby increasing receptor sensitivity, but did not affect the early rising phase of the response. BAPTA also slowed the adaptation of the response to steady illumination. 6. These results indicate that cytoplasmic calcium concentration plays a similar role in the light adaptation of guinea‐pig rods to that in the adaptation of the rods and cones of lower vertebrates. Calcium therefore appears to act as the messenger of light adaptation in mammalian rods.
Na(+)‐ and H(+)‐gradient‐dependent transport of alpha‐aminoisobutyrate by luminal membrane vesicles from rabbit proximal tubule.
Authors: Jessen H , Vorum H , Jørgensen K E , Sheikh M I
Published: December 2014

1. The characteristics of renal transport of alpha‐aminoisobutyrate (AIB) by luminal membrane vesicles isolated from either the proximal convoluted part (pars convoluta) or the proximal straight part (pars recta) of rabbit proximal tubule were investigated. 2. Transport of AIB in vesicles from pars convoluta was mediated by both Na(+)‐dependent and Na(+)‐independent systems, which in the presence of an inwardly directed H+ gradient can drive the uphill transport of AIB into these vesicles. 3. By contrast, in luminal membrane vesicles from pars recta, transient accumulation of AIB was only dependent on Na+. Lowering pH without a H+ gradient (pHi = pH0 = 5.5) completely abolished the Na(+)‐dependent transient accumulation of AIB in these vesicle preparations. 4. Attempts to determine the stoichiometry of both the Na(+)‐AIB and H(+)‐AIB transporters located in these two segments of proximal tubule suggested that one Na+ and one H+ ion may be involved in the transport of AIB. 5. Sodium‐dependent uptake of AIB in vesicles from pars convoluta was competitively inhibited by L‐serine and L‐phenylalanine, whereas the presence of L‐proline, L‐alanine and glycine had no significant effect. By contrast, the H(+)‐gradient‐dependent uptake of AIB was drastically reduced (30% of the control value) by L‐proline, L‐alanine and glycine, while L‐serine and L‐phenylalanine had no significant effect. 6. On the other hand, pars recta vesicles exhibited a different transport specificity. L‐Phenylalanine, L‐serine, L‐alanine and glycine, but not L‐proline competitively inhibited the uptake of AIB, providing evidence for the existence of a common transport system for AIB, L‐phenylalanine, L‐serine, L‐alanine and glycine in this segment of rabbit proximal tubule.
Shortening of muscle fibres during stretch of the active cat medial gastrocnemius muscle: the role of tendon compliance.
Authors: Griffiths R I
Published: December 2014

1. The length of muscle fibres in the medial gastrocnemius (MG) muscle of the anaesthetized cat was measured using ultrasound techniques. During the course of ‘isometric’ contractions, the muscle fibres shortened by stretching the compliant tendons, until the muscle fibres could no longer produce enough force to stretch the tendons further. At optimal muscle length (Lo) the maximal shortening of muscle fibres was 28%. 2. At muscle lengths much longer than Lo, ‘isometric’ contractions produced a slow shortening of the muscle fibres as the tendons were stretched and this resulted in a slow rise in tension. This phenomenon, usually referred to as ‘creep’, is due to low power at long muscle fibre length. This study shows that the series compliance present in the tendons is the major contributor to ‘creep’ in the cat MG muscle. As the tendons stretched during the course of the contraction, the average sarcomere length became shorter providing greater filament overlap and increasing power. 3. Slow to medium speed stretches applied shortly after the onset of contraction, as occurs in cat MG during walking and trotting, were entirely taken up in the tendons and the muscle fibres actually shortened throughout the imposed muscle stretch. 4. When early stretches were applied at muscle lengths longer than Lo, stretch of the muscle resulted in a peak force that was less than if the stretch had not been applied. This was the reverse of the situation for stretches at lengths less than Lo. When stretch was applied after attaining peak force, the force was greatly enhanced and the muscle fibres were also stretched. 5. Using the same techniques in a freely walking cat, the muscle fibres shortened by 1.0 +/‐ 0.3 mm during the stance phase of the step‐cycle when the muscle was being stretched, in 198 consecutive step‐cycles. 6. The tendons act as a mechanical buffer to protect muscle fibres from damage during eccentric contractions. 7. Since stretches of the MG muscle are not faithfully imposed on the muscle fibres, studies of muscle spindle function during locomotion need to take into consideration these effects of tendon compliance. The dominant view, when the foot lands on the ground during normal locomotion, is that muscle spindles are stretched along with the muscle resulting in reflex enhancement of contractile force. This study shows that the muscle fibres do not stretch under these circumstances, except at high speeds of locomotion when the stretch rate is also high.
Effects of enhanced activity on synaptic transmission in mouse extensor digitorum longus muscle.
Authors: Dorlöchter M , Irintchev A , Brinkers M , Wernig A
Published: December 2014

1. Transmitter release at neuromuscular junctions of extensor digitorum longus (EDL) muscle in mice was studied after 2‐8 month periods of unforced running in wheels. 2. Intracellular recordings at 10 Hz stimulation revealed that the quantal content of endplate potentials (EPPs) in Mg(2+)‐blocked preparations was larger by 30% in trained (mean number of quanta, m = 1.75 +/‐ 0.19, n = 7) than in untrained control EDL muscles (m = 1.35 +/‐ 0.35, n = 7). Similarly the amplitudes of the first, maximum and plateau EPPs during tetanic stimulation (100 Hz for 1 s or 400 ms) in curare‐blocked preparations were increased by 28% each; muscle fibre diameters did not differ while other postsynaptic effects were not excluded. 3. Training effects became particularly evident in two pairs of monozygotic twins, in which the time courses of facilitation and depression were changed as well: at 100 Hz stimulation the maximum EPP amplitude was reached on average at 2.6 impulses in controls but at 2.0 impulses in runners, and the following decline below the value of the first EPP at 5.0 and 3.8 impulses respectively. 4. Block resistance, as monitored by isometric tension measurements in different presynaptic (Mg2+) and postsynaptic (curare) blocking solutions, was higher in trained than in control EDL muscles. Depression in a train of four nerve‐evoked single twitches at 2 Hz was lower. 5. As expected from the unchanged fibre diameters (see above) isometric tetanic force was similar in trained and control EDL muscles. Muscle fatigue resistance was larger in trained animals and succinic dehydrogenase activity was higher in fibres of trained muscles indicating an endurance training of the EDL muscle. 6. It is concluded that besides changes in muscle fibre properties, prolonged elevated activity causes increased transmitter release in EDL muscles. As a consequence, the safety margin of transmission in trained EDL muscles is markedly elevated.
Activation and desensitization of the 5‐HT3 receptor in a rat glioma x mouse neuroblastoma hybrid cell.
Authors: Yakel J L , Shao X M , Jackson M B
Published: December 2014

1. Tight‐seal voltage‐clamp techniques were used to study the 5‐HT3 receptor of differentiated NG108‐15 cells. 2. The inward current caused by 5‐HT was dependent on the 5‐HT concentration: the apparent dissociation constant was 3.3 microM and the Hill coefficient was 1.8. 3. Immediately after establishing a recording, sustained application of a saturating concentration of 5‐HT caused the response to decline with a half‐time of 0.57 s (at a membrane potential of ‐70 mV). The time course of desensitization was best fitted by a sum of two exponentials. 4. Desensitization became slower during the first 10 min of recording in the whole‐cell configuration, with the half‐time for response decay increasing to 1.8 s. The deceleration of desensitization may result from wash‐out of a cytoplasmic regulator of the receptor. 5. Desensitization declined less during whole‐cell recordings when patch pipettes contained non‐hydrolysable analogues of adenosine 5'‐triphosphate. 6. Desensitization developed more rapidly following the addition of forskolin, prostaglandin E1, cholera toxin or 1,9‐dideoxyforskolin to the recording medium. Non‐hydrolysable adenosine 5'‐phosphate analogues had no effect on the enhancement of desensitization induced by forskolin.
Factors released from endocardium of the ferret and pig modulate myocardial contraction.
Authors: Smith J A , Shah A M , Lewis M J
Published: December 2014

1. In isolated heart muscle preparations, selective removal of the endocardium results in a characteristic and unusual negative inotropic effect. Possible mechanisms for this effect were investigated in this study. 2. In endocardium‐intact preparations of ferret papillary muscle, 8‐bromo‐cyclic GMP, sodium nitroprusside, atrial natriuretic peptide (ANP) and substance P each induced changes in contractile behaviour similar to selective endocardial removal, and each significantly elevated myocardial cyclic GMP levels. Substance P failed to elevate myocardial cyclic GMP levels following removal of endocardium or in the presence of haemoglobin, suggesting that it may act by releasing endothelium‐derived relaxing factor (EDRF) from endocardium. However, there was no change in myocardial cyclic GMP levels following endocardium removal alone. 3. In cascade bioassay experiments, it was confirmed that porcine cultured endocardial cells released an unstable humoral agent whose effects on an endothelium‐denuded pig coronary artery were indistinguishable from EDRF. 4. The negative inotropic effects of endocardium removal were reversed in bioassay experiments where an endocardium‐denuded papillary muscle was exposed to the effluent from a column of porcine cultured endocardial cells on microcarrier beads. This demonstrates for the first time the release of a ‘contraction prolonging factor’ from endocardium, the tonic release of which would explain the negative inotropic effect of endocardium removal. 5. It is concluded that elevation of ferret papillary muscle cyclic GMP (as for example with EDRF) produces changes in contractile performance similar to those induced by endocardium removal. We also demonstrate that superfused porcine cultured endocardial cells release a humoral agent (provisionally named ‘endocardin’) which causes reversal of the changes in mechanical properties seen after endocardial removal.
Calcium regulation of ciliary beat frequency in human respiratory epithelium in vitro.
Authors: Di Benedetto G , Magnus C J , Gray P T , Mehta A
Published: December 2014

1. The changes in ciliary beat frequency (CBF) of human nasal respiratory epithelial cells were measured in vitro with a photometric technique following exposure to either 4‐bromo‐calcium ionophore A23187 (4‐Br‐A23187) or trifluoperazine (TFP), an inhibitor of calmodulin‐sensitive calcium‐dependent protein kinases. Changes in intracellular free calcium concentrations in response to 4‐Br‐A23187 were studied using a fluorescent dye (Fura‐2). 2. Addition of 10(‐5) M‐4‐Br‐A23187 caused a time‐dependent (P less than 0.01) rise in CBF. The increment in CBF was statistically significant 10 min after challenge (+10%; P less than 0.01) and was sustained for at least 1 h, with maximal stimulation after 40 min (+ 18%; P less than 0.01). 3. Exposure to 10(‐5) M‐4‐Br‐A23187 caused an immediate increase in intracellular free calcium concentration, which preceded the rise in CBF. 4. TFP (10(‐4) M) caused a reduction of baseline CBF (‐10%; P less than 0.01) and prevented the expected rise when the cells were subsequently exposed to 10(‐5) M‐4‐Br‐A23187. 5. We conclude that: (1) calcium ionophore stimulates the CBF of human respiratory cells; (2) this effect is mediated through a calmodulin‐sensitive system, since it is abolished in the presence of TFP; (3) the same pathway appears to control the basal CBF of these cells, since TFP also decreases CBF.
Intestinal absorption of the intact peptide carnosine in man, and comparison with intestinal permeability to lactulose.
Authors: Gardner M L , Illingworth K M , Kelleher J , Wood D
Published: December 2014

1. Healthy humans ingested the dipeptide carnosine (L‐beta‐alanyl‐L‐histidine). Their plasma levels and urinary outputs of carnosine and beta‐alanine were monitored over the following 5 h. 2. Large amounts of intact carnosine (up to 14% of the ingested dose) were recovered in the urine over the 5 h after ingestion. However, carnosine was undetectable in the plasma unless precautions were taken to inhibit blood carnosinase activity ex vivo during and after blood collection. 3. The amount of carnosine recovered in urine varied substantially between subjects. It correlated negatively with carnosinase enzymic activity in the plasma. Highest carnosinase activities were observed in those subjects who regularly underwent physical training. 4. Urinary recovery of the disaccharide lactulose also varied considerably between subjects, but was substantially lower than that of carnosine. There was no significant correlation between the recoveries of carnosine and lactulose. 5. When lactulose was ingested with a hypertonic solution, the urinary recovery of lactulose was generally increased. When carnosine was ingested with a hypertonic solution, the urinary recovery of carnosine was reduced: hence the paracellular route probably is not dominant for absorption of intact carnosine. 6. Intact carnosine must have crossed the intestine to an extent much greater than hitherto recognized. Rapid post‐absorptive hydrolysis is a severe obstacle to quantification of intact peptide absorption.
Activation and inactivation of excitation‐contraction coupling in rat soleus muscle.
Authors: Dulhunty A F
Published: December 2014

1. Potassium (K+) contractures have been used to characterize the processes of activation and inactivation of excitation‐contraction coupling during prolonged depolarization of fibres in small bundles dissected from rat soleus muscles at 23 degrees C. 2. The smallest measurable K+ contracture tension was recorded with depolarization to ‐40 mV in 30 mM‐K+ and maximum tension was achieved between ‐26 mV in 80 mM‐K+ and ‐19 mV in 120 mM‐K+. 3. The rate of inactivation of K+ contracture tension was voltage dependent. Tension decayed from 80 to 20% of the peak amplitude within 44.0 +/‐ 2.2 s at ‐26 mV (in 80 mM‐K+), compared with 66.7 +/‐ 4.8 s at ‐35 mV (in 40 mM‐K+). Results are given as mean +/‐ 1 S.E.M. 4. The effect of inactivation on maximum tension was determined using a two pulse protocol in which a ‘conditioning’ depolarization in solutions containing 20‐120 mM‐K+ was applied for 0.5‐10 min before a ‘test’ depolarization to ‐8 mV in 200 mM‐K+. The amplitude of the test contracture was compared with the mean amplitude of ‘control’ 200 mM‐K+ contractures elicited in normally polarized fibres immediately before and after the two pulse protocol. Conditioning depolarization to ‐47 mV (in 20 mM‐K+) did not reduce test 200 mM‐K+ contracture tension. Significant inactivation was seen with further conditioning depolarization to more positive potentials: after 10 min at ‐40 mV (in 30 mM‐K+), or ‐35 mV (in 40 mM‐K+), test 200 mM‐K+ contracture tension was reduced by 33 and 70% respectively. 5. In contrast to amphibian muscle, where maximum tension falls to zero within a few minutes of depolarization to potentials positive to ‐50 mV, test 200 mM‐K+ contracture tension in rat soleus fibres fell initially rapidly and then slowly, but was not reduced to zero, even after 10 min at ‐19 mV in 120 mM‐K+. 6. The fast phase of inactivation of test 200 mM‐K+ contracture tension occurred during the decay of the conditioning K+ contracture. The slow phase of inactivation reached completion after 10 min of conditioning depolarization and occurred during the period when conditioning tension was reduced to zero or to a plateau level. Both phases of inactivation in rat soleus fibres are slow compared with fast and slow inactivation times of 5‐100 s respectively reported for amphibian muscle. 7. When repolarized after prolonged depolarization, the muscle fibres were initially refractory, i.e. unable to produce tension in response to electrical stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)
Morphine actions on supraoptic oxytocin neurones in anaesthetized rats: tolerance after i.c.v. morphine infusion.
Authors: Pumford K M , Leng G , Russell J A
Published: December 2014

1. The effects of acute i.v. administration of morphine on putative oxytocin neurones of the supraoptic nucleus were studied in urethane‐anaesthetized female rats which had been exposed to i.c.v. infusion of morphine (up to 50 micrograms h‐1) or vehicle for 5 days. 2. In vehicle‐infused rats, i.v. morphine inhibited the spontaneous activity of six out of seven putative oxytocin neurones. Increasing doses of morphine were given, from 1 microgram kg‐1 to 5 mg kg‐1. The median cumulative threshold dose to produce significant inhibition was 20 micrograms kg‐1 (seven cells in six rats); six out of seven cells were inhibited at 161 micrograms kg‐1. The highest doses tested inhibited by approximately 90% (excluding one unaffected cell). Inhibition was fully reversed by i.v. naloxone without overshoot, indicating a lack of acute dependence. 3. Injection of morphine i.c.v. inhibited firing at doses that were ineffective by i.v. injection and the effects of i.c.v. morphine were reversed by i.v. naloxone. 4. Acute morphine (500 micrograms kg‐1 i.v.) reduced the plasma concentration of oxytocin, measured after 15 min by specific radioimmunoassay, by 34% (n = 14). 5. In lactating rats i.c.v. injection of morphine (1‐2 micrograms) inhibited the activity of supraoptic neurones identified as oxytocinergic by their responses to suckling. 6. In seventeen rats infused with i.c.v. morphine the initial firing rate of twenty‐eight spontaneously active, non‐phasic neurones was significantly less, by 24%, than thirty‐four similar cells in control rats, indicating incomplete tolerance to i.c.v. morphine. Morphine (up to 161 micrograms kg‐1 given i.v.) inhibited none of nine active non‐phasic neurones (P less than 0.01 compared to control rats), but at higher doses inhibited four of nine cells; the overall median threshold cumulative dose (1660 micrograms kg‐1) was significantly greater than in vehicle‐infused controls, indicating tolerance to i.v. morphine. In contrast with control rats, some cells (5/9) were modestly excited by low doses of morphine. Naloxone (5 mg kg‐1 i.v.) produced withdrawal excitation: the firing rate of putative oxytocin neurones increased to approximately 260% of the pre‐i.v. morphine value, indicating dependence in mechanisms regulating the firing rate of these neurones. 7. In morphine‐infused rats, the basal firing rate of nineteen phasically active, putative vasopressin supraoptic neurones was not different in nineteen phasic cells in controls (6.4 +/‐ 0.7 vs. 4.2 +/‐ 0.6 Hz). 8. Thus morphine potently inhibits the firing of magnocellular oxytocin neurones in the female rat, inhibiting oxytocin secretion. Morphine tolerance and dependence develop during i.c.v. infusion of morphine for 5 days. Similar tolerance to and dependence upon endogenous opioids during pregnancy may be important in the preparation of oxytocin neurones for parturition.
An intracellular analysis of the visual responses of neurones in cat visual cortex.
Authors: Douglas R J , Martin K A , Whitteridge D
Published: December 2014

1. Extracellular and intracellular recordings were made from neurones in the visual cortex of the cat in order to compare the subthreshold membrane potentials, reflecting the input to the neurone, with the output from the neurone seen as action potentials. 2. Moving bars and edges, generated under computer control, were used to stimulate the neurones. The membrane potential was digitized and averaged for a number of trials after stripping the action potentials. Comparison of extracellular and intracellular discharge patterns indicated that the intracellular impalement did not alter the neurones' properties. Input resistance of the neurone altered little during stable intracellular recordings (30 min‐2 h 50 min). 3. Intracellular recordings showed two distinct patterns of membrane potential changes during optimal visual stimulation. The patterns corresponded closely to the division of S‐type (simple) and C‐type (complex) receptive fields. Simple cells had a complex pattern of membrane potential fluctuations, involving depolarizations alternating with hyperpolarizations. Complex cells had a simple single sustained plateau of depolarization that was often followed but not preceded by a hyperpolarization. In both simple and complex cells the depolarizations led to action potential discharges. The hyperpolarizations were associated with inhibition of action potential discharge. 4. Stimulating simple cells with non‐optimal directions of motion produced little or no hyperpolarization of the membrane in most cases, despite a lack of action potential output. Directional complex cells always produced a single plateau of depolarization leading to action potential discharge in both the optimal and non‐optimal directions of motion. The directionality could not be predicted on the basis of the position of the hyperpolarizing inhibitory potentials found in the optimal direction. 5. Stimulation of simple cells with non‐optimal orientations occasionally produced slight hyperpolarizations and inhibition of action potential discharge. Complex cells, which had broader orientation tuning than simple cells, could show marked hyperpolarization for non‐optimal orientations, but this was not generally the case. 6. The data do not support models of directionality and orientation that rely solely on strong inhibitory mechanisms to produce stimulus selectivity.
Properties of single fast chloride channels from rat cerebral cortex neurons.
Authors: Blatz A L
Published: December 2014

1. Properties of Cl‐ channels from surface membranes of acutely dissociated rat cerebral cortical neurons were studied with the patch clamp technique. These channels were present in the majority of excised inside‐out membrane patches. 2. Cl‐ channels were rarely observed in cell‐attached membrane patches, and usually several minutes elapsed following excision of the patch before Cl‐ channels became active. 3. Under asymmetric ionic conditions (1000 mM‐KCli, 140 mM‐KClo), neuronal Cl‐ channels are fairly selective for Cl‐ over K+ and Na+, with permeability ratios, determined by reversal potential shifts of 4.8 for both PCl/PK and PCl/PNa. 4. Neuronal Cl‐ channel kinetic activity remained stable over periods of time long enough to collect up to 500,000 open and closed intervals. Occasionally, the channels entered altered modes of activity. In the ‘buzz mode’ the open and closed interval durations became much shorter than normal for several hundreds of intervals. In the 'subconductance mode’ the channel opened to a current level about two‐thirds of the normal level. 5. Using the method of maximum likelihood, sums of exponentials were fitted to the distributions of open and closed interval durations. Open interval distributions required at least two exponential components with time constants of less than 1 ms. At least six or seven exponential components were required to fit the closed interval distributions with time constants ranging from 30 microseconds to several hundreds of milliseconds. This suggests that neuronal Cl‐ channels enter at least two open and six or seven closed kinetic states during normal activity. 6. Cl‐ channels often entered long‐duration closed states of several minutes which could not be accounted for by the sums of exponentials fitted to the distribution of closed interval durations. 7. Neuronal Cl‐ channels exhibit a marked voltage dependence with the percentage of time the channels are open increasing with depolarization. Most of the observed voltage dependence can be accounted for by a decrease in the mean closed interval duration with depolarization. The mean open interval was relatively independent of voltage. 8. These results suggest a high degree of similarity in kinetic behaviour and conductance properties between the fast Cl‐ channels of tissue‐cultured rat skeletal muscle and fast Cl‐ channels in acutely dissociated rat cerebral cortical neurons.
Influence of mild cold on the components of 24 hour thermogenesis in rats.
Authors: Brown D , Livesey G , Dauncey M J
Published: December 2014

1. The influence of two weeks' acclimation to either 28 degrees C (thermal neutrality) or 21 degrees C (mild cold) on 24 h heat production and motor activity has been investigated in male Wistar rats. Food intake was controlled and provided as a single meal of approximately 170 kJ per day. Mathematical modelling was used to relate metabolic rate to measured movement and time of day. 2. For animals at thermal neutrality it was clear that metabolic rate increased during periods of substantial measured movement and returned to baseline during periods of minimal activity. Total heat production could therefore be divided into two components: underlying and movement‐induced thermogenesis. 3. At 21 degrees C, a more complex model was needed. During periods of substantial activity, the relation between metabolic rate and movement was similar to that at 28 degrees C and total heat production could be divided into the same two components of underlying and movement‐induced thermogenesis. However, during periods of prolonged inactivity, a different model was required, which included a component of extra metabolic activity, termed supplementary thermogenesis. By fitting this model to data at 28 and 21 degrees C, it was possible to partition 24 h heat production into the three possible sources of underlying, movement‐induced and supplementary thermogenesis. 4. Total 24 h heat production was approximately 25% higher for rats at 21 compared with 28 degrees C (P less than 0.01) and underlying thermogenesis was approximately 20% higher for those in the mild cold (P less than 0.01). Measured movement was significantly reduced in the mild cold (P less than 0.05) although it was energetically less efficient since there was no difference in movement‐induced thermogenesis, which accounted for 18 and 15% of total heat production at 28 and 21 degrees C respectively. Supplementary thermogenesis was observed only in the mild cold and it accounted for approximately 6% of 24 h heat production, while the peak value accounted for 20% of total heat production. Circadian variations in thermogenesis were also different at 28 compared with 21 degrees C. Possible mechanisms accounting for the components of underlying thermogenesis and supplementary thermogenesis are discussed.
Neuromuscular transmission at newly formed neuromuscular junctions in the regenerating soleus muscle of the rat.
Authors: Grubb B D , Harris J B , Schofield I S
Published: December 2014

1. A study of neuromuscular function in regenerating skeletal muscle fibres in the rat soleus muscle has been made. The muscle fibres were damaged in vivo by the injection of the myotoxic venom component notexin, and then allowed to regenerate spontaneously. 2. Regenerating muscle fibres generated action potentials and contracted following direct intracellular stimulation as early as 4 days after the injection of notexin. 3. Miniature endplate potentials (MEPPs) were recorded at a minority of synapses at 3 days, and from all synapses by 5 days. The mean amplitude of MEPPs in a given fibre was directly proportional to muscle fibre input resistance. 4. Spontaneous transmitter release in the regenerating fibres was relatively insensitive to changes in [K+]0 but the effect of Ruthenium Red on spontaneous release was similar in the regenerating and control muscle fibres. 5. Functional innervation, defined as the ability to generate an indirect action potential, was restored in 97% of fibres by 10 days. The generation of an action potential was always associated with a twitch of the muscle fibre. Those fibres that were unable to generate an action potential usually exhibited a low membrane potential (ca ‐50 mV). These fibres could generate action potentials if they were hyperpolarized using an intracellular current‐passing microelectrode. 6. The quantal content of endplate potentials (EPPs) was estimated from the mean EPP and mean MEPP amplitudes in cut muscle fibre preparations. These estimates suggested that quantal content was low at the earliest stages of regeneration, but increased as the muscle fibres matured and became normal at 10‐21 days. 7. During repetitive stimulation at 30 Hz there was a fall in the amplitude of EPPs of 40‐45%. The fall was similar in regenerating and control fibres. Conducting synapses never exhibited failure to generate an EPP during the period of high‐frequency stimulation.
Changes in excitability of human motor axons underlying post‐ischaemic fasciculations: evidence for two stable states.
Authors: Bostock H , Baker M , Reid G
Published: December 2014

1. We have investigated the origin of post‐ischaemic ectopic discharges in human nerve by recording changes in electrical excitability following periods of ischaemia (15‐20 min) sufficient to induce spontaneous motor fasciculations. The ulnar nerve was stimulated beneath a pressure cuff on the upper arm, and compound motor action potentials recorded from abductor digiti minimi. 2. On releasing the cuff after 15 min of ischaemia, thresholds to short current pulses increased in two distinct phases: a slow phase followed by a rapid rise to a peak threshold. The rapid rise was too fast to track (i.e. 100% threshold increase in less than 4 s), and was sometimes followed after 30‐40 s by an equally rapid fall. Small polarizing currents affected the timing of the rapid threshold increase, as if it was occurring at a particular membrane potential. 3. By recording complete stimulus‐response curves every few seconds, we found that the rapid threshold changes were associated with a bimodal distribution of thresholds. Most fibres were found in either a high‐threshold or low‐threshold state, and these two states converged over a period of about 10 min. 4. Spontaneous motor fasciculations were only recorded after the rapid rise in threshold and when the fibres existed in two threshold states. The spontaneous activity was not responsible for inducing the two states, since they could also be recorded in its absence. 5. A computer model of a human motor axon node and internode was constructed, incorporating channel types demonstrated in other axons, and channel densities adjusted to match the responses of human axons to depolarizing and hyperpolarizing current pulses. An increase in extracellular potassium concentration produced a region of negative slope conductance in the current‐voltage relationship of the model, and the appearance of two stable states with enhanced activity of the electrogenic sodium pump. 6. Transitions between the two stable states of the model could account qualitatively for the rapid threshold changes recorded from post‐ischaemic axons. In the model, spontaneous action potentials occurred following some transitions from the high potential state to the low potential state. We suggest that post‐ischaemic motor fasciculations in man also involve transitions between two equilibrium states, occurring in axons with high extracellular potassium and high electrogenic pump activity.
Dependence of Na+ pump current on external monovalent cations and membrane potential in rabbit cardiac Purkinje cells.
Authors: Bielen F V , Glitsch H G , Verdonck F
Published: December 2014

1. The effect of membrane potential and various extracellular monovalent cations on the Na+ pump current (Ip) was studied on isolated, single Purkinje cells of the rabbit heart by means of whole‐cell recording. 2. Ip was identified as current activated by external K+ or its congeners NH4+ and Tl+. The current was blocked by dihydroouabain (1‐5 x 10(‐4) M) over the whole range of membrane potentials tested. 3. In Na(+)‐containing solution half‐maximum Ip activation (K0.5) occurred at 0.4 mM‐Tl+, 1.9 mM‐K+ and 5.7 mM‐NH4+ (holding potential, ‐20 mV). 4. The pump current (Ip)‐voltage (V) relationship of the cells in Na(+)‐containing media with K+ or its congeners at the tested concentrations greater than K0.5 displayed a steep positive slope at negative membrane potentials between ‐120 and ‐20 mV. Little voltage dependence of Ip was observed at more positive potentials up to +40 mV. At even more positive potentials Ip measured at 2 and 5.4 mM‐K+ decreased. 5. Lowering the concentration of K+ or its congeners below the K0.5 value in Na(+)‐containing solution induced a region of negative slope of the Ip‐V curve at membrane potentials positive to ‐20 mV. 6. The shape of the Ip‐V relationship remained unchanged when the K+ concentration (5.4 mM) of the Na(+)‐containing medium was replaced by NH4+ or Tl+ concentrations of similar potency to activate Ip (20 mM‐NH4+ or 2 mM‐Tl+). 7. In Na(+)‐free, choline‐containing solution half‐maximum Ip activation occurred at 0.13 mM‐K+ (holding potential, ‐20 mV). 8. At negative membrane potentials the positive slope of the Ip‐V curve was flatter in Na(+)‐free than in Na(+)‐containing media. A reduced voltage dependence of Ip persisted, regardless of whether choline ions or Li+ were used as a Na+ substitute. 9. Lowering the K+ concentration of the Na(+)‐free, choline‐containing solution to 0.05 mM evoked an extended region of negative slope in the Ip‐V relationship at membrane potentials between ‐40 and +60 mV. 10. It is concluded that the apparent affinity of the Na(+)‐K+ pump towards K+ in cardiac Purkinje cells depends on both the membrane potential and the extracellular Na+ concentration. 11. The region of negative slope of the Ip‐V curve observed in cells which were superfused with media containing low concentrations of K+ or its congeners strongly suggests the existence of at least two voltage‐sensitive steps in the cardiac Na(+)‐K+ pump cycle.(ABSTRACT TRUNCATED AT 400 WORDS)
Sodium currents in smooth muscle cells freshly isolated from stomach fundus of the rat and ureter of the guinea‐pig.
Authors: Muraki K , Imaizumi Y , Watanabe M
Published: December 2014

1. Inward currents elicited by depolarization from holding potentials of ‐80 to ‐10 mV in single smooth muscle cells isolated from stomach fundus of the rat and ureter of the guinea‐pig had two components. The initial fast component (Ifi) was activated and mostly inactivated within 1‐2 and 10 ms, respectively, at 21 degrees C. The following sustained component (Isi) lasted over 50 and 500 ms in fundus and ureter cells, respectively. Ifi was blocked by tetrodotoxin but not affected by 0.5 microM‐mu‐conotoxin in both types of cells. Isi was abolished by the substitution of extracellular Ca2+ with Mn2+. 2. The sensitivity of Ifis to TTX was markedly different in fundus and ureter cells. The half‐inhibition was obtained at 870 and 11 nM, respectively. The amplitude of Ifi was highly dependent on extracellular Na+ concentration in a solution containing 2.2 mM‐Mn2+ and 0 mM‐Ca2+ in both cells. It is concluded that Ifis in these cells are TTX‐sensitive and mu‐conotoxin‐insensitive Na+ currents. 3. Some of the kinetics of INa measured at 10 degrees C were markedly different in fundus and ureter cells. The current‐voltage relationships for Ifi in fundus and ureter cells had peaks at about ‐10 and 0 mV, respectively. The voltage dependence of the steady‐state inactivation of Ifi was also significantly different in these cell types. The half‐inactivation voltages were about ‐74 and ‐45 mV, respectively. The recovery time course from inactivation in fundus cells was about 10 times slower than that in ureter at ‐80 mV, where it was 25 ms. 4. The contribution of Ifi to the rising phase of an action potential was examined using TTX under current clamp mode at 21 degrees C. A fast notch‐like potential elicited by a subthreshold stimulus for action potential generation was blocked by TTX in both types of cells. Action potentials elicited by a stimulus around threshold were occasionally suppressed by TTX, whereas an action potential was never observed when extracellular Ca2+ was replaced with Mn2+. 5. In conclusion, the existence of at least two types of Na+ channel currents, which were distinguished by their TTX sensitivity and kinetics, was strongly suggested in smooth muscle cells from the rat fundus and the guinea‐pig ureter. INa in these cells may have a physiological role to accelerate the generation of an action potential by triggering a rapid activation of ICa, while not being essential for activation of action potentials.