bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of tachycardia on right atrial dynamics and plasma atrial natriuretic factor in anaesthetized rabbits.
Authors: King K A , Ledsome J R
Published: December 2014

1. The effect of tachycardia on right atrial pressure (RAP) and dimensions (RAD) and plasma immunoreactive atrial natriuretic factor (IR‐ANF) was examined in anaesthetized rabbits before and after the administration of atenolol. 2. Small increases in plasma IR‐ANF occurred during pacing at 6 Hz and after the administration of atenolol (0.4 mg kg‐1). A significantly greater increase in IR‐ANF occurred during pacing in the presence of atenolol. 3. Despite a significant rise in mean RAP, systolic RAD (SRAD) and diastolic RAD (DRAD) did not change during tachycardia. Systolic RAD increased after the administration of atenolol while both SRAD and DRAD increased during pacing in the presence of atenolol. 4. Systolic right atrial wall stress (SRAS) increased during tachycardia, did not change after the administration of atenolol, and increased during pacing in the presence of atenolol. Minute SRAS followed a similar pattern of changes except that it decreased after atenolol. 5. Diastolic right atrial wall stress (DRAS) did not change during tachycardia, and increased both after atenolol and after pacing in the presence of atenolol. Tachycardia led to an increase in minute DRAS; a significantly greater increase in minute DRAS occurred during tachycardia in the presence of atenolol. 6. The absence of alterations in RAD during tachycardia suggests that the release of ANF in response to tachycardia is not due to simple mechanical stretch of the atria. Both systolic and diastolic atrial wall stress may be determinants of ANF release: the influence of systolic factors appears to predominate during tachycardia while diastolic factors appear to be the major determinants of the effects of atenolol.
Calcium‐dependent chloride current in neurones of the rabbit pelvic parasympathetic ganglia.
Authors: Akasu T , Nishimura T , Tokimasa T
Published: December 2014

1. Voltage‐clamp recordings were made from neurones in rabbit vesical pelvic ganglia by using single microelectrodes filled with 2 M‐caesium chloride. Neurones were superfused with Krebs solution containing 300 nM‐tetrodotoxin and 50 mM‐tetraethylammonium. 2. Depolarizing voltage jumps activated inward currents followed by slowly decaying inward tail currents at ‐30 to +30 mV, which were accompanied by a large increase in membrane conductance. Both the inward current and tail current were blocked by cobalt (2 mM) or in a Krebs solution containing zero calcium and 12 mM‐magnesium. 3. Substitution of barium for calcium enhanced the inward current, while it strongly reduced the tail current. Strontium substitution still exhibited both the inward current and the tail current. 4. Lowering external chloride activity increased the tail current amplitudes without affecting an initial calcium current. The reversal potentials of the tail current, measured using a twin‐pulse protocol, were ‐18 +/‐ 5 mV (mean +/‐ S.E.M., n = 8) and +5 +/‐ 3 mV (n = 5) in Krebs solution and low‐chloride (62 mM) solution, respectively, suggesting a calcium‐dependent chloride current. 5. Stilbene derivatives, 4‐acetamido‐4'‐isothiocyanostilbene‐2,2'‐disulphonic acid (SITS, 0.01‐1 mM) and 4,4'‐diisothiocyanostilbene‐2,2'‐disulphonic acid (DIDS, 0.01‐1 mM), reversibly and concentration dependently depressed the tail current without affecting the calcium current. 6. Transient (T) and sustained (N and L) types of calcium current were likely to co‐exist in neurones of the rabbit pelvic ganglia. Calcium‐dependent chloride current was activated by N‐ and L‐type calcium currents but not by T‐type current. 7. Activation of the tail current at 0 to +20 mV was described by a single‐exponential function. The tail current decayed exponentially at a holding membrane potential of ‐70 mV. Tail decay time constants were dependent on voltage and duration of the step command. 8. Substantial activation of the calcium‐dependent chloride conductance could occur during a post‐tetanic after‐potential when pelvic ganglia neurones fired action potentials repetitively.
Feed‐forward inhibitory potentials and excitatory interactions in guinea‐pig hippocampal pyramidal cells.
Authors: Turner D A
Published: December 2014

1. The patterns of inhibition in the CA1 region of the rat hippocampus were evaluated by focal proximal and distal stratum radiatum stimulation, during intracellular recording. The characteristics of isolated inhibitory responses and the interactions of excitatory and inhibitory potentials were analysed. 2. The amplitude of minimal inhibitory postsynaptic potentials (IPSPs) evoked by both proximal and distal stimulation averaged ‐0.51 +/‐ 0.24 mV (mean +/‐ S.D.; n = 32). These responses demonstrated little variability from trial to trial and showed no net trends in amplitude at a stimulation rate of 1 Hz. 3. Minimal IPSPs demonstrated a short latency to onset (2.90 +/‐ 1.58 ms for proximal and 3.64 +/‐ 1.39 ms for distal) at stimulation levels which were insufficient to evoke an extracellular field potential. Thus, minimal IPSPs were recruited through feed‐forward circuitry, based on the rapid onset and the lack of activation of recurrent collaterals. 4. The minimal IPSPs showed a similar 10‐90% rise time for proximal and distal responses. However, the half‐width and decay time constant (from the peak) were more prolonged for the distal stimulation, indicating that a late IPSP component was evoked primarily by the distal stimulation. This late component was not observed in isolation at low stimulation intensities. 5. The conductance transient underlying the IPSPs was calculated using a neurone cable model. The proximal IPSP responses were simulated by an alpha input function (at the soma) with a peak conductance in the range of 2.5‐45 nS (alpha = 1.75; reversal potential ‐1.0 to ‐10 mV). The distal IPSP shape was only partially reproduced by a longer single transient (alpha = 1.25), suggesting the presence of a second, slower component. However, insufficient data on this slower component precluded a more exact simulation of the distal IPSP response. 6. Analysis of interactions between minimal excitatory postsynaptic potentials (EPSPs) and IPSPs showed that often the rising as well as the falling phase of the EPSP could be affected by the IPSP. At small stimulation levels, minimal EPSPs and IPSPs were closely overlapping, but the IPSPs were of significantly longer duration than EPSP responses. 7. The composite EPSP waveform shape became progressively truncated with increasing afferent stimulation. Feed‐forward inhibition limited the time course of excitation to a narrow window, approximately 3‐5 ms wide. Feed‐forward postsynaptic inhibition significantly limited both the duration and the overall efficacy of small EPSPs in CA1 pyramidal neurones.
Decreased sensitivity of contraction to changes of intracellular pH in papillary muscle from diabetic rat hearts.
Authors: Lagadic‐Gossmann D , Feuvray D
Published: December 2014

1. The relationship between intracellular pH (pHi) and contractile activity was investigated in papillary muscles isolated from right ventricle of normal and streptozotocin (STZ)‐induced diabetic rats. pHi changes induced by 20 mM‐NH4Cl were recorded with H(+)‐sensitive microelectrodes. 2. An increase in pHi of approximately 0.20 pH units on exposure to NH4Cl led to an increase of the maximum developed tension, which was 707.8 +/‐ 57.5% (mean +/‐ S.E. of mean, n = 10) of control in normal muscles and 271 +/‐ 16.3% (n = 10) in diabetic muscles. On the other hand, acidosis induced by NH4Cl withdrawal was associated with a fall in developed tension to 48.2 +/‐ 6.7% of control in diabetic muscles, as compared to 79.2 +/‐ 8% in normal muscles. 3. The decrease in tension associated with acidosis was rapidly followed (in approximately 2 min) by a transient redevelopment of force, which peaked at 80.2 +/‐ 8.6% of control in the diabetic muscles as compared to 153.5 +/‐ 11.7% in normal papillary muscles. The peak of this secondary positive inotropy coincided in both groups of muscles with the maximum decrease of pHi, i.e. ‐0.40 +/‐ 0.02 and ‐0.28 +/‐ 0.04 pH units in diabetic and normal muscles, respectively. 4. Caffeine (10 mM), which had a marked positive inotropic effect in both groups of muscles, abolished the transient recovery of tension occurring after NH4Cl withdrawal. Ryanodine (2 microM) which had a marked negative inotropic effect on both normal and diabetic papillary muscles, also suppressed the transient recovery of tension. 5. The presence of amiloride (1 mM) during acidosis induced by NH4Cl withdrawal abolished the observed differences in developed tension, in particular the transient recovery of tension, between normal and diabetic muscles, as it abolished the differences in the amplitude of pHi decrease and in the time course of pHi recovery. 6. The presence of 2',4'‐dichlorobenzamil amiloride (40 microM) significantly and similarly delayed and reduced the amplitude of transient recovery of tension in both normal and diabetic papillary muscles. 7. We conclude that STZ‐induced diabetes induces a decrease in pHi sensitivity of contractile force. This may be the consequence of a change in sarcoplasmic reticulum (SR) composition and function, and may also indirectly result from changes in Na(+)‐H+ exchange activity, particularly during intracellular acidosis.
The effects of taurine on Ca2+ uptake by the sarcoplasmic reticulum and Ca2+ sensitivity of chemically skinned rat heart.
Authors: Steele D S , Smith G L , Miller D J
Published: December 2014

1. Caffeine (10 mM) induced a transient contracture in saponin‐treated cardiac trabeculae as a result of Ca2+ release from the sarcoplasmic reticulum (SR). Regular cycles of uptake and release were repeated to stabilize responses. The SR accumulated Ca2+ during the period prior to the addition of caffeine and this was reflected in the size of the caffeine contracture. Increasing the time for Ca2+ loading between successive caffeine exposures resulted in an increase in the amplitude of the contracture. Similarly, the size of the contracture was a function of the calcium ion concentration [( Ca2+]) in the preceding loading period. 2. Taurine (microM‐40‐mM), when included in both loading and caffeine solutions, markedly potentiated the caffeine‐induced contracture. The effect occurs even if taurine was included only in the loading solutions. The potentiating effect was ascribed to a direct action of taurine on the SR, since taurine did not significantly change the [Ca2+] in the loading solutions. 3. The maximal effect of taurine was produced at approximately 5 mM; higher taurine concentrations caused a lesser potentiation of the caffeine contracture. If the solutions were balanced with respect to osmolarity the effect of taurine did not decline at high concentrations. 4. If the [Ca2+] in the loading solutions was increased to produce a caffeine‐induced contracture that peaked close to maximal Ca2(+)‐activated force, taurine caused a fall in the size of contracture and a more variable response. This result could be explained by an increase in the spontaneous release of Ca2+ from the SR in the presence of taurine. 5. In Triton‐skinned trabeculae, taurine (1 mM‐40 mM) increased the Ca2+ sensitivity of the contractile proteins in a dose‐dependent manner but had little effect on maximum Ca2(+)‐activated force. The increase in Ca2+ sensitivity was small: in a typical experiment 30 mM‐taurine reduced the [Ca2+] necessary for half‐maximal activation from 3.02 to 2.56 microM, with no significant change in the shape of the relationship.
Pyloric motor function during emptying of a liquid meal from the stomach in the conscious pig.
Authors: Treacy P J , Jamieson G G , Dent J
Published: December 2014

1. In six conscious pigs antral, pyloric and duodenal pressures were recorded with a 5.5 cm sleeve sensor and multiple perfused side holes. The manometric assembly was positioned by dual point transmucosal potential difference measurement. Gastric emptying was measured by drainage of the proximal duodenum through a Thomas cannula. Pressures were correlated with emptying of ingested radiolabelled 5% dextrose. Alteration of emptying was produced by infusion into the more distal duodenum of nutrient and non‐nutrient solutions of differing osmolalities. 2. Motor activity of the pylorus and antrum was stimulated by ingestion and modulated by intraduodenal infusion. Duodenal infusion of normal saline was associated with antro‐pyloric pressure waves and rapid emptying of the ingested liquid. Duodenal infusion of dextrose, fatty acid, amino acids and hyperosmolar saline was associated with stimulation of isolated pyloric pressure waves, suppression of antral pressure waves and slowing of gastric emptying. 3. The dose‐response relationship of these effects was investigated using varying rates of intraduodenal dextrose infusions. The emptying rate of the ingested liquid was inversely related to the rates of delivery of dextrose to the duodenum, directly related to the rate of antro‐pyloric pressure waves and inversely related to the rate of isolated pyloric pressure waves. 4. Clearly defined episodes of pulsatile flow produced slightly more than half of the total emptying that occurred. This pulsatile flow was intimately associated in time with antro‐pyloric pressure waves. Sequences of isolated pyloric pressure waves were associated with near cessation of emptying. When there were periods of absent pyloric antral pressure waves, flow rates intermediate between the rapid emptying of pulsatile flow during antro‐pyloric pressure waves and the near cessation of flow during isolated pyloric pressure waves occurred. 5. The findings suggest a major role for the pylorus in the control of emptying of liquids from the stomach, both as a component of an antro‐pyloric peristaltic pump and as a resistor to transpyloric flow during nutrient and hyperosmolar stimulation of duodenal receptors.
Tonic vibration reflexes elicited during fatigue from maximal voluntary contractions in man.
Authors: Bongiovanni L G , Hagbarth K E
Published: December 2014

1. In the present study on human foot dorsiflexor muscles we have examined the effects of high‐frequency (150 Hz) muscle vibration on weak or moderate voluntary contractions (maintained by constant effort) and on maximal voluntary contractions (MCVs) of (i) non‐fatigued muscles, (ii) muscles fatigued by sustained MVCs and (iii) muscles deprived of gamma‐fibre innervation by partial anaesthetic nerve block. The motor outcome of the voluntary dorsiflexion efforts was assessed by measuring the firing rates of single motor units in the anterior tibial (TA) muscle, the mean voltage EMG activity from the pretibial muscles and foot dorsiflexion force. 2. With the subject instructed to exert constant effort in maintaining a weak or moderate contraction, superimposed vibration caused an enhancement of EMG activity and contraction force. 3. Previous claims that muscle vibration has no facilitatory effect on motor output in MVCs were found to hold true for non‐fatigued but not for fatigued muscles. Thus, the fatigue‐induced decline in EMG activity and motor unit firing rates was counteracted by short periods (less than 10‐20 s) of superimposed vibration. However, with longer vibration periods it seemed as if the initial facilitation converted into an opposite effect which accentuated the fatigue‐induced decline in motor output and contraction force. 4. Like muscle fatigue, a partial anesthetic block of the deep peroneal nerve, supposedly interrupting transmission in gamma‐motor fibres, caused a reduction of MVC motor unit firing rates which could be counteracted by muscle vibration. In prolonged MVCs performed during the block, motor unit firing rates did not show the normal progressive decline from an initially high level, but stayed at a relatively constant low level throughout the contraction period. 5. Even though alternative interpretations are possible, the results agree with the hypotheses (i) that in sustained MVCs, fatigue processes occur not only in extrafusal but also in intrafusal muscle fibres, (ii) that the intrafusal fatigue leads to a reduction of the voluntary drive conveyed to the alpha‐motoneurones via the gamma‐loop and (iii) that vibration‐induced activity in group Ia afferents can act as a substitute for the diminished fusimotor drive.
Membrane currents in visually identified motoneurones of neonatal rat spinal cord.
Authors: Takahashi T
Published: December 2014

1. Ionic currents induced by depolarization of motoneurones were analysed by tight‐seal, whole‐cell recording in thin slices of neonatal rat lumbar spinal cord. Identification of motoneurones viewed under Nomarski optics was confirmed by retrograde labelling with the fluorescent dye, Evans Blue. 2. Under whole‐cell voltage clamp, depolarizing command pulses from a holding potential of about ‐70 mV evoked a fast inward current followed by an outward current. The former was suppressed either by lowering external Na+ concentration or by application of tetrodotoxin (TTX). The apparent dissociation constant of TTX was about 13 nM. 3. The outward current remaining after TTX application was activated by depolarization above ‐50 mV, showing marked outward rectification in the current‐voltage relation. Outward tail currents reversed in polarity near the K+ equilibrium potential calculated from the external and pipette K+ concentrations. 4. When external Ca2+ was replaced by Mg2+, the outward K+ current was suppressed markedly and reversibly. Subtraction of current recorded in Ca2+‐free‐Mg2+ solution from that in control solution revealed a Ca2(+)‐dependent K+ current, IK(Ca) with both a transient, IC, and a sustained component IAHP; its tail current lasted for several hundred milliseconds. 5. The sustained outward current observed in Ca2(+)‐free‐Mg2+ solution was largely suppressed by external application of tetraethylammonium chloride (30 mM), suggesting that it was mostly the delayed rectifier current, IK. In Ca2(+)‐free‐Mg2+ solution containing TEA and TTX, another transient outward current was observed, which was inactivated by depolarizing pre‐pulses in a time‐ and voltage‐dependent manner. The steady‐state inactivation curve indicated 50% inactivation at about ‐77 mV. 4‐Aminopyridine (4‐AP, 4 mM) largely and reversibly suppressed this current, whereas it did not affect IK observed in the absence of TEA. It is suggested that the transient outward current corresponds to the A‐current (IA). 6. Action potentials were recorded in current‐clamp mode. Replacement of external Ca2+ by Mg2+ markedly diminished the after‐hyperpolarization. Concomitantly, the repolarizing phase of action potentials was slightly prolonged. In Ca2(+)‐free‐Mg2+ solution, application of 4‐AP markedly prolonged action potential repolarization. In Ca2(+)‐free‐Mg2+ solution containing 4‐AP, addition of TEA‐Cl further prolonged the duration of the action potential. It is concluded that three different potassium currents, IC, IA and IK may all contribute to action potential repolarization in rat spinal motoneurones.
The membrane properties and firing characteristics of rat jaw‐elevator motoneurones.
Authors: Moore J , Appenteng K
Published: December 2014

1. We have determined the membrane and firing properties of fifty‐six jaw‐elevator motoneurones in rats that were anaesthetized with pentobarbitone, paralysed and artificially ventilated. 2. Forty‐two neurones were identified as masseter motoneurones and fourteen as masseter synergist motoneurones. The membrane potentials for the sample ranged from ‐60 to ‐86 (mean = ‐68; S.D. = 7.3; n = 56), and spike amplitudes from 50 to 95 mV. The duration of the after‐hyperpolarization following antidromic spikes in masseter motoneurones ranged from 15 to 50 ms (mean = 30; S.D. = 12.8) and their amplitudes from 1.0 to 4.5 mV (mean = 2.7; S.D. = 2.2; n = 42). 3. The mean input resistance for the total sample was 2.3 M omega (S.D. = 0.9; n = 56), membrane time constant 3.9 ms (S.D. = 0.9; n = 48) and rheobase 4.2 nA (S.D. = 2.6; n = 56). The distribution of these parameters was independent of membrane potential. We found no significant interrelationships between the membrane properties and one interpretation of this is that our sample may be drawn from a homogenous population of motoneurones. We also suggest that elevator motoneurones may have a lower Rm (specific membrane resistivity) value than cat hindlimb motoneurones because they have a similar range of input resistance values but only half the total surface area. 4. Forty‐six out of forty‐nine neurones fired repetitively to a depolarizing current pulse at a mean threshold of 1.6 x rheobase. Current‐frequency plots were constructed for thirteen neurones and all but one showed a primary and secondary range in the firing of the first interspike interval. The mean slope in the primary range was 31 impulses s‐1 nA‐1 and 77 impulses s‐1 nA‐1 for the secondary range. The mean minimal firing frequency for steady firing was 26 impulses s‐1 and, in response to an increase of stimulation, the rate increased monotonically with a slope of 11 impulses s‐1 nA‐1. 5. The dynamic sensitivity of twelve neurones was assessed from their response to ramp waveforms of current of constant amplitude but varying frequencies (0.2‐2 Hz). Firing initially increased along a steep slope up to a frequency of between 40 and 60 impulses s‐1 and then increased along a much shallower slope. Both the threshold for eliciting firing and the firing at the transition point of the two slopes remained constant with changes in ramp frequency.(ABSTRACT TRUNCATED AT 400 WORDS)
Active potassium absorption in rat distal colon.
Authors: Sweiry J H , Binder H J
Published: December 2014

1. Active potassium (K+) absorption in rat distal colon was investigated by measuring mucosal‐to‐serosal (JK, ms) and serosal‐to‐mucosal (JK, sm) 42K+ fluxes (mu equiv h‐1 cm‐2) across isolated stripped mucosa under short‐circuit conditions in normal and dietary Na‐depleted animals. As previously demonstrated, removal of Na+ from both mucosal and serosal solutions bathing the normal colon slightly increased net K+ absorption as a result of inhibition of JK, sm without affecting JK, ms, while in the Na‐depleted group net K+ secretion (‐0.54 +/‐ 0.11) was converted to a marked net K+ absorption (1.68 +/‐ 0.30, P less than 0.001). 2. In both groups of animals in Na(+)‐free Ringer solution, JK, ms exhibited saturable and linear components, while JK, sm was a linear function of [K+]. Estimated affinity constants (mM) for saturable net K+ absorption were similar in normal (0.52 +/‐ 0.12) and Na‐depleted (0.67 +/‐ 0.11) animals; however, there was a greater than 3‐fold increase in the saturable flux (Jmax) from 0.54 +/‐ 0.04 in the normal colon to 1.78 +/‐ 0.08 mu equiv h‐1 cm‐2 in Na‐depleted animals. 3. Mucosal orthovanadate (100 microM) inhibited JK, ms in both normal (control, 0.66 +/‐ 0.05 vs. orthovanadate, 0.36 +/‐ 0.03 mu equiv h‐1 cm‐2, P less than 0.001) and Na‐depleted animals (control 1.20 +/‐ 0.13 vs. orthovanadate 0.77 +/‐ 0.07 mu equiv h‐1 cm‐2, P less than 0.01) without affecting JK, sm or the short‐circuit current. In the Na‐depleted group mucosal omeprazole or SCH28080 (100 microM), inhibitors of gastric K(+)‐H(+)‐ATPase, insignificantly or slightly reduced (by 10%) JK, ms respectively; in contrast, mucosal ouabain (1 mM) markedly inhibited JK, ms (control, 1.61 +/‐ 0.16 vs. ouabain, 0.83 +/‐ 0.98 mu equiv h‐1 cm‐2, P less than 0.001). 4. Mucosal Na+ appeared to be a competitor of K+ uptake across the apical membrane. 5. These results indicate that dietary Na‐depletion increases electroneutral K+ absorption by increasing its transport capacity and suggest that the mechanism of this active K+ absorption process may involve an apical K(+)‐ATPase with properties that are unlike the gastric K(+)‐H(+)‐ATPase but similar, in part, to Na(+)‐K(+)‐ATPase.
Development of L‐glutamate‐ and glycine‐activated currents in spinal cord neurones during early chick embryogenesis.
Authors: Baev K V , Rusin K I , Safronov B V
Published: December 2014

1. The membrane currents elicited by L‐glutamate and glycine applications in morphologically different neurone types were investigated in isolated spinal cord cells from the lumbar enlargement of 6 to 11‐day‐old chick embryos. The whole‐cell patch‐clamp technique and concentration clamp methods have been used. Isolated spinal cord neurones of four stages were investigated: 6, 7.5, 9 and 11 days of incubation (29th, 32nd, 35th and 37th stages of development, respectively). 2. The L‐glutamate‐activated conductance consisted of desensitizing and non‐desensitizing components. The Hill coefficient for the first component was 1, and for the second was 2. The number of cells responding to L‐glutamate application with only a desensitizing component decreased from 53.4% on the 6th day of incubation to 6.7% on the 11th day, whereas the number of cells responding with bicomponent responses increased during the same period from 13.3 to 87%. 3. From the 6th and 11th day of chick embryo development the characteristics of the desensitizing component of L‐glutamate‐activated conductance remained constant (half‐maximal dose, (ED50 = 2.6 +/‐ 0.3 mM) whereas the ED50 for the non‐desensitizing component decreased 10 times. 4. It was found that the density of the desensitizing L‐glutamate‐activated ionic current increased during morphological and age‐dependent differentiation of spinal cord cells. 5. Of the investigated cells 88.7% were sensitive to glycine application. The smallest percentage of neurones responding to glycine application was observed at 7.5 days of incubation. Glycine‐activated conductance did not change at the investigated stages (ED50, 71 +/‐ 2 microM; Hill coefficient, 2). 6. A significant decrease in the glycine‐activated current density was observed on the 9th day of incubation in multipolar neurones with three neurites, against a tendency to an increase of glycine‐activated ionic currents during morphological and age‐dependent differentiation of cells. 7. Of the investigated cells 78% were sensitive to both glycine and L‐glutamate application. A negative correlation between glycine‐ and L‐glutamate‐activated current densities (correlation coefficient, ‐0.71) was revealed by means of statistical analysis. 8. We conclude that these changes in chemosensitivity of the spinal cord neurones may underlie the increase in locomotor activity of the chick embryo observed on the 9th day of incubation.
Mechanisms of caffeine activation of single calcium‐release channels of sheep cardiac sarcoplasmic reticulum.
Authors: Sitsapesan R , Williams A J
Published: December 2014

1. Calcium‐release channels of sheep cardiac junctional sarcoplasmic reticulum were incorporated into planar phospholipid bilayers. Single‐channel current fluctuations were recorded under voltage clamp conditions. 2. Channels incorporate into the bilayer with a fixed orientation and channel open probability is regulated by the calcium concentration at the cytosolic face of the membrane. 3. Addition of caffeine (0.5‐2.0 mM) to the cytosolic side of the membrane increased the open probability of the calcium‐activated calcium‐release channel by increasing the frequency of opening without significant alteration to the durations of open events. This effect was observed at both 0.1 and 10 microM‐activating cytosolic calcium. 4. Caffeine (0.5‐2.0 mM) did not activate the channel at a subactivating cytosolic calcium concentration (80 pM). 5. At subactivating calcium concentrations, channels could be activated by higher concentrations of caffeine (greater than 5.0 mM) revealing a second, calcium‐independent, mechanism for channel activation. Channel openings induced by these high concentrations of caffeine at subactivating calcium concentrations displayed different kinetics from those observed with calcium as the sole activating ligand or with combinations of calcium and low concentrations of caffeine. 6. Activation of channel opening by caffeine in the presence of calcium did not affect single‐channel conductance. Channel openings produced by caffeine at subactivating cytosolic calcium concentrations had identical conductance and relative permeability to those seen on calcium activation. 7. Channels activated by caffeine at both activating and subactivating calcium concentrations were characteristically modified by ryanodine, Ruthenium Red, ATP and magnesium, implying that the same channel is involved under both conditions.
Responses of blood vessels in the rabbit knee to electrical stimulation of the joint capsule.
Authors: Ferrell W R , Khoshbaten A
Published: December 2014

1. An in vitro preparation of the rabbit knee joint, perfused with oxygenated Locke's solution, was used to study the response of articular blood vessels to electrical stimulation of the joint capsule. 2. Using trains of stimulus pulses of different durations, frequency‐response curves were obtained. Electrical stimulation always produced vasoconstriction of joint blood vessels, which increased as a function of both frequency and pulse width. 3. This vasoconstrictor response was neurally mediated as it was markedly inhibited after addition to both bath and perfusate of tetrodotoxin. In addition, the response to field stimulation of the capsule was virtually abolished in animals pretreated with reserpine which depletes sympathetic nerve endings of noradrenaline. 4. The response to electrical stimulation was substantially reduced by the alpha‐adrenergic antagonist phenoxybenzamine (10(‐5) M), the alpha 1‐blocker prazosin (10(‐6) M), and by guanethidine (10(‐5) M) which inhibits the release of noradrenaline, ATP and neuropeptide Y from sympathetic nerve endings. 5. The attenuation of the vasoconstrictor response to field stimulation by prazosin (10(‐6) M) was little altered by addition of the alpha 2‐adrenoceptor blocker rauwolscine (10(‐6) M) to the perfusate. 6. alpha, beta‐Methylene ATP (10(‐6) M), a P2‐purinoceptor desensitizer, had no effect on the vasoconstrictor response to electrical stimulation. 7. These results indicate that the vasoconstrictor response to electrical stimulation of the rabbit knee joint capsule is mediated via noradrenaline acting upon alpha 1‐adrenoceptors.
A voltage‐clamp study of the electrophysiological characteristics of the intramural neurones of the rat trachea.
Authors: Allen T G , Burnstock G
Published: December 2014

1. The electrophysiological characteristics of intramural neurones from the paratracheal ganglia of 14‐ to 18‐day‐old rats were studied in vitro using intracellular, single‐electrode current‐ and voltage‐clamp techniques. 2. Resting membrane potentials ranged between ‐50 and ‐73 mV. In 50‐60% of all neurones, random and occasionally patterned bursts of spontaneous, fast synaptic potentials were observed. In all cases, superfusion with either hexamethonium (100 microM), or Ca2(+)‐free, high‐magnesium‐containing solutions abolished all synaptic activity. 3. Two distinct patterns of spike discharge were observed in response to prolonged intrasomal current injection. Most cells (65‐75%) fired rhythmic, high‐frequency (50‐90 Hz) bursts of action potentials, with interburst intervals of between 300 and 500 ms, throughout the period of current stimulation. A further 10‐15% of cells fired tonically at low frequencies (10‐15 Hz) for the duration of the applied stimulus. In both cell types, trains of action potentials were followed by a pronounced calcium‐dependent after‐hyperpolarization which persisted for up to 3 s. The magnitude of the after‐hyperpolarization following a single spike in tonic‐firing cells was considerably larger than in burst‐firing cells. Both the action potential and the after‐hyperpolarization in all cells displayed a calcium‐dependent, tetrodotoxin‐resistant component which was abolished by the removal of the extracellular calcium. 4. The spike after‐hyperpolarization resulted from activation of an outward calcium‐dependent potassium current which reversed at ‐86.5 mV. This value was shifted by 63.6 mV for a 10‐fold increase in extracellular potassium concentration. 5. All of the cells studied exhibited marked outward rectification when depolarized. This resulted from activation of a time‐ and voltage‐dependent M‐current. The slow inward current relaxations associated with the M‐current became faster at more negative potentials and reversed around ‐85 mV. Raising the extracellular potassium concentration shifted the reversal potential for the current relaxations to more depolarized potentials in a manner predicted by the Nernst equation for a current carried by potassium ions. Both the outward current at depolarized potentials and the slow current relaxations were potently inhibited by extracellular BaCl2 (1 mM) but were unaffected by CsCl (1‐3 mM). 6. Inward rectification at hyperpolarized potentials was a characteristic of all cells. Membrane hyperpolarization revealed inward rectification in the ‘instantaneous’ current‐voltage relationship at membrane potentials greater than ‐80 mV.(ABSTRACT TRUNCATED AT 400 WORDS)
On a pseudo‐rebreathing technique to assess the ventilatory sensitivity to carbon dioxide in man.
Authors: Dahan A , Berkenbosch A , DeGoede J , Olievier I C , Bovill J G
Published: December 2014

1. The ventilatory sensitivity to carbon dioxide obtained from a step‐ramp CO2 challenge was compared to the CO2 sensitivity from the steady‐state method. 2. Experiments were performed in nine healthy male subjects against a background of hyperoxia and in two subjects against a background of normoxia. 3. In each subject experiments were performed in which the stepwise increase in end‐tidal PCO2 above its resting value (A) was varied (range 0‐2 kPa) and the subsequent rate of rise of end‐tidal PCO2 in time (R) kept constant at 0.6 or 0.8 kPa min‐1. 4. The results of the hyperoxic experiments show that the slope of the non‐steady‐state ventilatory response to CO2 (Sn) is greatly influenced by the magnitude of A. An increase of A of 1 kPa results in a 54% increase of the ratio non‐steady‐state ventilatory CO2 sensitivity to steady‐state ventilatory CO2 sensitivity (Ss). The magnitude of R plays a minor role in determining Sn. The normoxic experiments gave similar results. 5. In experiments performed during hyperoxia Sn approximates Ss when the magnitude of A is 0.5 kPa. 6. The results are discussed and related to a physiological model. Simulations with representative values for the model parameters are in fair agreement with experimental values.
Discharge of vagal pulmonary receptors differentially alters neural activities during various stages of expiration in the cat.
Authors: St John W M , Zhou D
Published: December 2014

1. The purpose was to evaluate the hypothesis that neural expiration is composed of two phases: I, a post inspiratory period; and II, the period at which expiratory activities of spinal nerves reach peak values. We hypothesized that the discharge of pulmonary stretch receptors might differentially alter neural activities during these two phases. 2. Activities of the phrenic nerve, intercostal nerve and nerves innervating the thyroarytenoid muscle of the larynx and triangularis sterni muscle of the chest wall were recorded in decerebrate and paralysed cats. 3. The experimental animals were ventilated with a servo‐respirator which produced changes in tracheal pressure, and lung volume, in parallel with alterations in integrated activity of the phrenic nerve. 4. In order to assess the influence of the discharge of slowly adapting pulmonary stretch receptors upon neural activities during expiration, lung volume was held at end‐expiratory or end‐inspiratory levels for individual respiratory cycles. 5. When pulmonary inflation was prevented, phrenic activity increased, as did activity of the thyroarytenoid nerve during early expiration. In contrast, activities of the triangularis sterni and intercostal nerves during mid‐ to late expiration declined. 6. Holding the lungs at end‐inspiratory levels caused a reduction of thyroarytenoid activity and increases in peak triangularis sterni and intercostal activities. Neural expiration typically continued as long as the lungs were maintained at the end‐inspiratory level. 7. Responses were qualitatively similar in hypocapnia, normocapnia and hypercapnia, but the magnitude of changes in neural activities was typically augmented with elevations in end‐tidal fractional concentrations of CO2. 8. We conclude that the discharge of slowly adapting pulmonary stretch receptors inhibits neural activities during early expiration and augments activities during mid‐to late expiration. Hence, our data support the concept that neural expiration is composed of two stages in which neural activities may be differentially controlled.
Regeneration and recovery of cat muscle spindles after devascularization.
Authors: Barker D , Scott J J
Published: December 2014

1. We have assessed the sensory reinnervation and recovery of regenerated muscle spindles in extensor digitorum longus (EDL) 6, 8 and 13 weeks after the muscle, with its nerve left intact, had been devascularized. Recordings were made from the dorsal roots of the responses of single afferent fibres to ramp‐and‐hold stretch of the regenerated spindles whose sensory reinnervation was subsequently examined in teased, silver preparations. 2. The spindle population in four normal EDL muscles ranged from 53 to 83 (mean 69); analysis of the afferent innervation of 166 normal b1b2c spindles showed that 23% had primary endings supplied by two Ia afferents. Regenerated spindles were identified as belonging to one of four groups in which afferents establish sensory endings on intrafusal muscle fibres in groups 1‐3, but not in group 4. Sensory reinnervation was complete after 6 weeks recovery and similar proportions of group 1‐3 spindles occurred after each recovery period, i.e. 58% after 6 weeks, 65% after 8 weeks and 62% after 13 weeks. We estimate that about half the original spindle population was lost owing to persistent ischaemic necrosis; that 30% regenerated and acquired functional afferent connections (group 1‐3 spindles); and that the total loss of spindle afferents was over 60%. 3. The conduction velocities of the regenerated spindle afferents were very similar to those of normal EDL spindle afferents. The proportions that responded normally to ramp‐and‐hold stretch at the end of each recovery period increased from 58% after 6 weeks to 61% after 8 and 88% after 13. Other responsive spindle afferents were either predominantly phasic or only responded to supramaximal stretch. The proportions of these decreased as recovery progressed reducing from 19% after 6 weeks to 9% after 13 weeks in the case of those giving predominantly phasic responses and from 23% after 6 weeks to 3% after 13 weeks in the case of those unresponsive to physiological stretch. 4. The mean peak and held firing rates of regenerated spindle afferents responsive to 10 mms‐1 ramp‐and‐hold stretches were all significantly lower than normal. There was no marked trend towards higher firing rates after longer periods of recovery through, considered separately, the mean peak firing rates of the normally responding afferents did show a distinct improvement. The mean dynamic and velocity indexes were not significantly different from normal. 5. The ratio of Ia:spindle II afferents, as identified by their responses to stretch, was 1:1.22 in the control animals and 1:1.26 in the experimental series.(ABSTRACT TRUNCATED AT 400 WORDS)
Permeation of calcium through excitatory amino acid receptor channels in cultured rat hippocampal neurones.
Authors: Iino M , Ozawa S , Tsuzuki K
Published: December 2014

1. N‐methyl‐D‐aspartate (NMDA)‐, quisqualate‐ and kainate‐induced currents were recorded in cultured rat hippocampal neurones using the whole‐cell voltage‐clamp technique. To isolate the inward currents carried by Ca2+ and other divalent cations (Sr2+, Ba2+, Mn2+ and Mg2+), both Na+ and K+ in the control external solution were replaced with the impermeant cation N‐methylglucamine (NMG). 2. Replacement of Na+, K+ and Ca2+ with NMG abolished NMDA‐, quisqualate‐ and kinate‐induced inward currents. In Na(+)‐, K(+)‐free (abbreviated simply as Na(+)‐free) solution containing 10 mM‐Ca2+ NMDA caused prominent inward currents at ‐60 mV. In this solution with the internal solution containing 165 mM‐Cs+, the reversal potential of the NMDA‐induced current was ‐5.0 +/‐ 0.7 mV (n = 36), indicating a value of PCa/PCs = 6.2 for the ratio of the permeability coefficients of Ca2+ and Cs+ according to the constant‐field equation. 3. NMDA elicited inward current responses at ‐60 mV in Na(+)‐, Ca2(+)‐free solution containing 10 mM‐Sr2+, Ba2+, or Mn2+, but not in Na(+)‐free, 10 mM‐Mg2+ solution. On the basis of reversal potential measurements, the permeability sequence of NMDA receptor channels among the divalent cations was determined to be Ba2+ (1.2) greater than Ca2+ (1.0) greater than Sr2+ (0.8) greater than Mn2+ (0.3) much greater than Mg2+ (less than 0.02). 4. The reversal potential of the quisqualate‐induced current was more negative than ‐80 mV in Na(+)‐free, 10 mM‐Ca2+ solution, indicating a value of PCa/PCs less than 0.18. 5. Kainate‐induced current responses were classified into two types. In the type I response the reversal potential of the kainate‐induced current was more negative than ‐80 mV in Na(+)‐free, 10 mM‐Ca2+ solution, indicating that the Ca2+ permeability of this type of kainate channel is as low as that of the quisqualate channel. In the neurones which showed a type I response, there was a tendency of outward rectification in the current‐voltage plots of the kainate response in control solution. 6. In the type II response kainate caused prominent inward currents at ‐60 mV in Na(+)‐free, 10 mM‐Ca2+ solution. The reversal potential was ‐23.3 +/‐ 5.6 mV (n = 17), indicating a permeability ratio PCa/PCs = 2.3. In the neurones which showed a type II response, a remarkable inward rectification was observed in the current‐voltage plots of the kainate response in control solution. 7. Type II kainate channels showed relatively poor selectivity among divalent cations.(ABSTRACT TRUNCATED AT 400 WORDS)
Two distinct types of inwardly rectifying K+ channels in bull‐frog atrial myocytes.
Authors: Clark R B , Nakajima T , Giles W , Kanai K , Momose Y , Szabo G
Published: December 2014

1. Single atrial myocytes were enzymatically isolated from the bull‐frog as previously described (Hume & Giles, 1981), and patch‐clamp techniques were used in an attempt to identify and separate two inwardly rectifying K+ channels in this tissue. 2. Single‐channel measurements consistently demonstrated the existence of two different resting K+ channels, which both exhibited strong inward rectification. The unitary conductances of these K+ channels were 34 +/‐ 4 and 22 +/‐ 3 pS (mean +/‐ S.D., at 22‐24 degrees C) when measured with 110 mM‐K+ in the pipette solution, and their mean open times were 0.87 +/‐ 0.33 and 129.9 +/‐ 49.4 ms, respectively. 3. In the absence of acetylcholine (ACh) in the pipette, openings of the larger channels with the shorter open times occurred at a very low frequency. When ACh was present in the patch pipette, the activity of this channel increased significantly, although the single‐channel conductance and gating behaviour were very similar either with or without ACh in the pipette. 4. The zero‐current voltage (extrapolated from the inward currents through these types of channels) depended on the extracellular K+ concentration. [K+]o, in the fashion expected for a predominantly K(+)‐selective channel: it shifted by 58 mV for a tenfold change in [K+]o. Very similar results were obtained from whole‐cell voltage‐clamp measurements (53 mV for a tenfold change in [K+]o). 5. The conductance of both types of K+ channels depended on [K+]o. The single‐channel conductances were 25 +/‐ 3 and 13 +/‐ 2 pS with 50 mM [K+]o, and 19 +/‐ 4 and 9 +/‐ 2 pS with 20 mM [K+]o, respectively. 6. These results demonstrate that two types of resting inwardly rectifying K+ channels can be identified in single atrial myocytes. One of these is an inwardly rectifying K+ channel (IK1) previously identified in whole‐cell voltage‐clamp experiments (Hume & Giles, 1983). The second channel is the muscarinic receptor‐regulated K+ channel (IK(ACh) which was first described in mammalian nodal and atrial cells. 7. N‐Ethylmaleimide (NEM), a reagent which alkylates sulphydryl groups, affects these two types of K+ channels differentially. In the cell‐attached patch configuration, bath application of NEM (50 microM) completely abolished the activity of IK(ACh), without affecting the IK1 channel activity. 8. To obtain further evidence that these two currents, IK1 and IK(ACh), were different, the inside‐out patch‐clamp technique was used.(ABSTRACT TRUNCATED AT 400 WORDS)
Sensitivity to flow of intrinsic gating in inwardly rectifying potassium channel from mammalian skeletal muscle.
Authors: Burton F L , Hutter O F
Published: December 2014

1. Current through inwardly rectifying K+ channels was measured in inside‐out patches from rat and human sarcolemmal vesicles and from dispersed rat flexor digitorum brevis muscle fibres. The patches were positioned so as to face the aperture of a large‐diameter pipette from which solution of the same composition as the bath solution could be ejected. The solution within the patch pipette and the bath solution both contained principally 140 mM‐KCl. 2. The kinetic behaviour of the inwardly rectifying channel was found to vary according to whether the patch was in static or flowing solution. At negative holding potentials, when the channel is open most of the time in static solution, flow produced a reversible and repeatable decrease in open probability. 3. In Mg2(+)‐free solution the inwardly rectifying channel allows outward current to pass at positive holding potentials. This allows the kinetic behaviour of the channel in static and flowing solution to be compared over a wider voltage range. 4. In both static and flowing solution, the open probability‐voltage relation is sigmoidal and can be fitted by a Boltzmann curve. As a result of flow, the maximum open probability at negative potentials is decreased and the mid‐point of the relation is shifted to the right by more than 20 mV. 5. No evidence could be found for the existence of a local concentration gradient sensitive to flow. Application of suction to the patch pipette showed the inwardly rectifying channels not to be sensitive to membrane stretch.(ABSTRACT TRUNCATED AT 250 WORDS)