bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel isoform of Ca2+ channel in rat fetal cardiomyocytes.
Authors: Tohse N , Masuda H , Sperelakis N
Published: December 2014

1. Single cardiomyocytes of 18‐day‐old rat fetuses were isolated to characterize the cardiac Ca2+ channels in the fetal period, using whole‐cell voltage clamp (Na+, K(+)‐free external solution and K(+)‐free internal solution), and depolarizing test pulses from a holding potential (HP) of ‐87 mV were applied. 2. The Ca2+ current was completely blocked by 2 mM‐CO2+, but not completely blocked by the dihydropyridine (DHP) Ca2+ antagonist nifedipine. Nifedipine (3 microM) decreased the amplitude of the current (at ‐7 mV) by 65.9 +/‐ 3.4% (n = 20). At a HP of ‐47 mV, nifedipine decreased the Ca2+ current to about the same degree. Diltiazem (1 microM) did not block the nifedipine‐resistant current which remained. 3. Nitrendipine, another DHP Ca2+ antagonist, had effects on the Ca2+ current similar to those of nifedipine. 4. The DHP‐resistant current was not blocked by T‐type channel blockers (Ni2+, tetramethrine) or an N‐type blocker (omega‐conotoxin). 5. In conclusion, rat fetal cardiomyocytes may have a unique type of Ca2+ channel (ICa(fe)), which decreases in amplitude and becomes less prominent during subsequent development.
Effect of perfusion pressure on force of contraction in thin papillary muscles and trabeculae from rat heart.
Authors: Schouten V J , Allaart C P , Westerhof N
Published: December 2014

1. Increased coronary perfusion leads to increased myocardial contraction and oxygen consumption (Gregg's phenomenon) even when oxygen supply is presumably sufficient. Previous studies concerned whole hearts, however, in which local hypoxia may play a role. We developed techniques for internal perfusion of thin papillary muscles from rat heart. The influence of perfusion pressure on muscle contraction was studied. We investigated whether Gregg's phenomenon is due to (a) hypoxia, (b) stretch of the muscle fibres, or (c) increased contractility. 2. The effectiveness of the perfusion technique was demonstrated in four ways: (a) the diameter of the capillaries increased with perfusion pressure; (b) 14 +/‐ 4% (mean +/‐ S.D., n = 11) increase in muscle diameter was observed on a change of perfusion pressure from 0 to 50 cmH2O; (c) addition of India ink to the perfusate caused rapid staining of the entire muscle; (d) during internal perfusion and external superfusion peak force was mainly determined by the [Ca2+] in the internal perfusate. 3. An increase of perfusion pressure from 0 to 70 cmH2O induced 74 +/‐ 20% (mean +/‐ S.D., n = 11) increase in peak force of contraction. In the absence of internal perfusion peak force was not affected by approximately 50% reduction of the PO2 in the bathing solution (from 700 to 350 mmHg). Hence, oxygen supply was not a limiting factor, i.e. the effect of internal perfusion on force was not related to hypoxia. 4. Segment length was measured with markers attached to the surface of the muscle. Perfusion‐induced changes in segment length were negligible (‐0.2 +/‐ 1.5%, n = 11). Force‐length relationships at different perfusion pressures show that the perfusion‐induced increase in force was generally larger than the maximum increase in force that could be induced by stretch. Furthermore, the time course of stretch and perfusion effects on force was different. We conclude that Gregg's phenomenon is not related to changes in fibre length, i.e. the hypothesis of pressure‐induced stretch ('garden hose' effect) does not apply to papillary muscles. 5. The pressure‐induced changes in the force‐length relationship were similar to the changes obtained with interventions that increase contractility, such as increased [Ca2+]. 6. Since hypoxia and length effects were not involved, and the effect of perfusion pressure was similar to that of inotropic interventions, we conclude that Gregg's phenomenon is a change in contractility. Possible explanations include changes in the ionic composition or volume of the interstitium, and inotropic factors produced by the endothelium or intramyocardial neurons.
Computer simulation of carbachol‐driven rhythmic population oscillations in the CA3 region of the in vitro rat hippocampus.
Authors: Traub R D , Miles R , Buzsáki G
Published: December 2014

1. We used simulations of the in vitro CA3 region of the hippocampus to analyse the 5 Hz population oscillations recorded experimentally in carbachol. 2. A simulation model of the in vitro CA3 region was constructed with 1000 pyramidal neurones and 200 inhibitory neurones (100 producing fast inhibitory postsynaptic potentials (IPSPs) and 100 producing slow IPSPs of delayed onset). Each neurone contained nineteen soma‐dendritic compartments. Pyramidal neurones contained six voltage‐ and/or calcium‐dependent ionic currents, whose kinetics were consistent with voltage‐clamp data. The connectivity and waveform of unitary synaptic events for excitatory and fast inhibitory synapses were consistent with dual intracellular recordings. This network was shown to generate previously described network oscillations, including synchronized bursts recorded in the presence of GABAA blockers, and synchronized synaptic potentials observed during partial blockade of GABAA inhibition. 3. The model generated 5 Hz oscillations as recorded in carbachol under the following conditions: (a) excitatory synaptic conductance was within a limited range; (b) there was blockade of fast and slow IPSPs (consistent with the experimental lack of effect of bicuculline and phaclofen on carbachol oscillations and the known depression of IPSPs by acetylcholine); (c) the after hyperpolarization (AHP) conductance was reduced (consistent with the known pharmacology of carbachol); (d) the apical dendrites of the pyramidal cells were depolarized, as suggested by the carbachol‐induced depolarization of pyramidal neurones. Each oscillation was associated in pyramidal cells with a burst of action potentials riding on a depolarizing wave. The N‐methyl‐D‐aspartate (NMDA) type of excitatory synapse was not necessary for the oscillations to occur. 4. Progressive reduction of excitatory synaptic strength led to an oscillation of the same frequency, with bursts riding on smaller EPSPs (consistent with the experiment). Further reduction of excitatory synaptic strength abolished the population oscillation by uncoupling the neurones. When excitatory synaptic conductance was too large, population oscillations were attenuated as the cells switched from a bursting mode to a repetitively firing mode. 5. Increasing the AHP conductance prolonged the interburst interval as expected. Inclusion of slow IPSPs exerted a similar effect. 6. When fast IPSPs were included, an oscillation with different characteristics emerged: a 10 Hz oscillation that was gated by compound GABAA IPSPs. On any oscillatory wave, few pyramidal neurones fired, and the firing of individual neurones was irregular.(ABSTRACT TRUNCATED AT 400 WORDS)
The role of endogenous angiotensin II in the regulation of renal haemodynamics and proximal fluid reabsorption in the rat.
Authors: Zhuo J , Thomas D , Harris P J , Skinner S L
Published: December 2014

1. The influence of endogenous angiotensin II (AII) on renal haemodynamics and tubular function was examined by clearance and micropuncture methods in anaesthetized rats during AII receptor blockade with the non‐peptide antagonist DuP 753 (50 micrograms kg‐1 min‐1 i.v.). 2. Mean arterial pressure was reduced slightly (‐5 +/‐ 2 mmHg) while filtration fraction and glomerular filtration rate rose by 30% without changes in renal plasma flow (RPF) or renal vascular resistance (RVR). 3. Fractional proximal fluid reabsorption (calculated from lithium clearance) fell from 73 to 64% (P < 0.01) and fractional distal sodium reabsorption decreased from 98 to 94% (P < 0.01). 4. Urine flow rate more than doubled, sodium output increased 4‐fold and plasma renin concentration rose 8‐fold while potassium excretion remained unchanged. 5. Proximal tubular fluid reabsorption (Jv) as measured by shrinking split‐droplet micropuncture decreased by 21% (P < 0.01) during infusion of DuP 753 compared with 22.5% (P < 0.01) during converting enzyme inhibition by enalaprilat (MK422). 6. Responses to DuP 753 were similar to those previously documented with converting enzyme inhibitors except that DuP 753 failed to raise RPF. It is concluded that generation of intrarenal vasodilator paracrines has confounded conclusions about the renal action of converting enzyme inhibitors and we propose that in anaesthetized rats, endogenous angiotensin II (AII) has its major renal influences on glomerular filtration and proximal fluid reabsorption with little effect on renal vascular resistance.
Acetylcholine released from guinea‐pig submucosal neurones dilates arterioles by releasing nitric oxide from endothelium.
Authors: Andriantsitohaina R , Surprenant A
Published: December 2014

1. The role of the endothelium as an effector of the neurogenic cholinergic vasodilatation in submucosal arterioles of the guinea‐pig ileum was investigated by measuring changes in arteriolar diameter in response to exogenous application of muscarine or electrical stimulation of the submucosal ganglia. 2. NG‐Monomethyl‐L‐arginine (L‐NMMA), an inhibitor of nitric oxide (NO) synthesis, competitively inhibited the vasodilatation produced by muscarine in arterioles which had been preconstricted with the prostaglandin analogue U46619. L‐Arginine (10 mM), but not D‐arginine (10 mM), prevented the inhibition by L‐NMMA. 3. Neither tetrodotoxin (TTX, 1 microM), nor the cyclo‐oxygenase inhibitor, indomethacin (10 microM), altered the muscarinic vasodilatation or the inhibitory effect of L‐NMMA. 4. Sodium nitroprusside (SNP), an activator of the soluble guanylate cyclase, dilated the arterioles in a concentration‐dependent manner. This vasodilatation was unaffected by L‐NMMA but was abolished by the guanylate cyclase inhibitor, methylene blue (10 microM). In addition, methylene blue antagonized the muscarinic vasodilatation to a similar degree as did L‐NMMA. 5. The vasodilatation produced by ganglionic stimulation (10 Hz, 10 s) was blocked by TTX and the muscarinic receptor antagonist, 4‐diphenylacetoxy‐N‐methyl‐piperidine methiodide (4‐DAMP, 1 microM). The neurally evoked vasodilatation was inhibited by 70% in the presence of L‐NMMA; this inhibition was prevented by L‐arginine. Methylene blue inhibited the neurogenic vasodilatation to the same extent as did L‐NMMA. 6. These results show that arteriolar vasodilatation by muscarine is mediated mainly through the release of NO formed from L‐arginine; the origin of the L‐arginine appears to be the endothelium. These results also demonstrate that acetylcholine released from submucosal nerves onto submucosal blood vessels reaches the endothelium to cause the release of NO formed from L‐arginine; the endothelial‐derived NO dilates the arteriole.
Synergistic action of cyclic GMP on catecholamine‐induced chloride current in guinea‐pig ventricular cells.
Authors: Ono K , Tareen F M , Yoshida A , Noma A
Published: December 2014

1. Effects of cyclic GMP on the catecholamine‐induced chloride current (ICl) were studied using the whole‐cell patch‐clamp technique combined with internal perfusion in single ventricular myocytes dispersed from guinea‐pig heart. 2. When ICl was activated by submaximal doses of isoprenaline (0.01‐0.1 microM), adrenaline (0.5‐1 microM) and histamine (0.2‐0.5 microM), intracellular dialysis with cyclic GMP (10‐100 microM) induced an extra increase of ICl. No further increase of ICl was induced by cyclic GMP when ICl was maximally activated. In the absence of agonists, cyclic GMP failed to induce ICl. 3. The enhancement by cyclic GMP was also observed when ICl was activated by external application of 0.2‐1.0 microM‐forskolin or by internal dialysis with a pipette solution containing 50‐200 microM‐cyclic AMP. 4. In contrast to cyclic GMP, 10‐1000 microM‐dibutyryl cyclic GMP and 8‐bromo‐cyclic GMP were ineffective in modifying ICl. 5. Milrinone (1‐10 microM), a specific inhibitor of a kind of phosphodiesterase which is inhibited by cyclic GMP, also enhanced ICl activated by submaximal doses of isoprenaline. Milrinone itself did not activate ICl. 6. When ICl was enhanced by 5 microM‐milrinone, an additional application of cyclic GMP failed to increase ICl. In the presence of cyclic GMP, milrinone failed to enhance ICl. 7. The above findings on ICl are analogous to the enhancement by cyclic GMP of the beta‐adrenergic stimulation of the Ca2+ current reported in the same preparation, and support the hypothesis that in mammalian cardiac cells cyclic GMP potentiates elevation of cyclic AMP induced by beta‐adrenergic agents, and thereby increases the amplitudes of ionic currents.
Extracellular divalent and trivalent cation effects on sodium current kinetics in single canine cardiac Purkinje cells.
Authors: Hanck D A , Sheets M F
Published: December 2014

1. The effects of the extracellular divalent cations barium, calcium, cadmium, cobalt, magnesium, manganese, nickel and zinc and the trivalent cation lanthanum on macroscopic sodium current (INa) were characterized in enzymatically isolated single canine cardiac Purkinje cells under voltage clamp at 9‐14 degrees C. 2. All di(tri)valent cations produced depolarizing shifts in the conductance‐voltage relationship. The order of efficacy, taken as the concentration required to produce a 5 mV shift in the mid‐point of peak INa conductance, from least to most effective was (mM): Ca2+ (2.97) approximately Mg2+ (2.67) approximately Ba2+ (1.93) > CO2+ (1.02) approximately Mn2+ (0.88) > Ni2+ (0.54) > La3+ (0.095) approximately Cd2+ (0.083) approximately Zn2+ (0.076). 3. Addition of di(tri)valent cations also produced depolarizing shifts in voltage‐dependent availability. The order of efficacy from the least to most effective was (mM): Cd2+ (7.70) approximately Mg2+ (6.86) approximately Ba2+ (4.50) > Ca2+ (2.47) approximately CO2+ (1.87) approximately Mn2+ (1.24) approximately Ni2+ (1.20) > Zn2+ (0.300) > La3+ (0.060). 4. The Gouy‐Chapman‐Stern equations were used to evaluate di(tri)valent cation efficacy in binding to surface charges. Surface charge density was estimated as 0.72 sites nm‐2, and it was assumed that Mg2+, the divalent cation that produced the smallest shift, screened but did not bind to surface charges. Based on voltage‐dependent availability, KD from lowest to highest affinity were (mM): Ba2+ (2500) > CO2+ (1670) approximately Mn2+ (1430) approximately Ca2+ = Cd2+ = Ni2+ (1200) > Zn2+ (250) > La3+ (30). 5. All di(tri)valent cations also produced a concentration‐dependent acceleration of INa tail current relaxation. The addition of Ca2+ and La3+ produced acceleration of tail current relaxations that could be accounted for by the surface charge effects predicted from the shift in voltage‐dependent availability. Cd2+, which produced almost no change in voltage‐dependent availability, dramatically accelerated tail current relaxation. Zn2+, Ni2+, Mn2+ and CO2+ also produced greater acceleration of tail current relaxation than could be accounted for by surface charge effects. 6. Di(tri)valent cations delayed time to peak INa in a concentration‐dependent manner. The time to peak INa‐voltage relationship was well described by an exponential plus a constant, and di(tri)valent cations did not affect the slope factor or constant but shifted the relationship in the depolarizing direction. Similar to their effect on tail currents, addition of some di(tri)valent cations produced larger effects on time to peak INa than expected from the shift of voltage‐dependent availability.(ABSTRACT TRUNCATED AT 400 WORDS)
Calcium transients caused by calcium entry are influenced by the sarcoplasmic reticulum in guinea‐pig atrial myocytes.
Authors: Lipp P , Pott L , Callewaert G , Carmeliet E
Published: December 2014

1. Single atrial myocytes obtained by enzyme perfusion from hearts of adult guinea‐pigs were investigated using whole‐cell voltage clamp and Indo‐1 micro‐fluorometry. 2. In myocytes loaded with a solution containing citrate as a low‐affinity, non‐saturable Ca2+ chelator, two types of [Ca2+]i transients could be recorded during repetitive activation of L‐type Ca2+ current. Both large and small [Ca2+]i transients occurred; large transients reached peak values of about 1 microM, and small transients were about 100 nM or less in amplitude. 3. In the case of the large transients, peak [Ca2+]i was usually reached with a variable delay after repolarization from a voltage step that activated calcium current (ICa). For the small transients the rise in [Ca2+]i paralleled ICa. Upon repolarization [Ca2+]i started to decay. 4. The small transients reflect entry of Ca2+ through Ca2+ channels (entry transients), whereas the large transients are due to entry and release from the sarcoplasmic reticulum (release transients). 5. The entry transients displayed a positive staircase pattern during trains of depolarizing voltage steps despite constant or even decreasing amplitude of ICa. The steepness of the staircase was increased by elevation of [Ca2+]o. Entry transients were always smallest immediately after a release transient. 6. After functional removal of the sarcoplasmic reticulum by caffeine (1‐5 mM) the staircase pattern of the transients reflecting Ca2+ entry was abolished. 7. It is concluded that the staircase pattern is due to rapid uptake by the sarcoplasmic reticulum of Ca2+ entering the cell, resulting in an attenuation of the signal. The attenuation is strongest shortly after a release signal, when the rate of sequestration of Ca2+ by the SR should be highest. 8. Evidence is provided that a compartment of the SR is involved in attenuation of the entry transients. This compartment has been identified recently as a peripheral release compartment.
Coherence between the sympathetic drives to relaxed and contracting muscles of different limbs of human subjects.
Authors: Wallin B G , Burke D , Gandevia S C
Published: December 2014

1. This study was undertaken to quantify the simultaneous sympathetic drives to muscles in the two legs of human subjects, and to elucidate the extent to which a common drive determines sympathetic outflow to different limbs at rest, during apnoea and during voluntary contractions. 2. Sympathetic efferent activity was recorded simultaneously from fascicles of both peroneal nerves, innervating the pretibial flexor muscles. At rest the similarity was quantified for a sample of records by manual measurement of equivalent bursts in the two recordings, and for all records by cross‐correlation and power spectral analysis of the two recordings. During contractions, only the latter method was used. 3. At rest the correlation coefficient for the relationship between the burst amplitudes for the two recordings was 0.72 (S.D. 0.1). For the same sequences, the computed coherence between the two recordings was 85.6% (S.D. 6.7%) at the cardiac period. There was a statistically significant linear relationship between these two measures of similarity, and this was stronger when data from sequences recorded during apnoea were included in the analysis. At rest the mean difference in coherence between consecutive sequences with no intervening manoeuvre (apnoea, contraction, change in recording site) was 4.2% (S.D. 4.3%). In only two of forty‐nine such instances was the difference in coherence > 10%. 4. Apnoea at end‐expiration increased the amplitude and frequency of sympathetic bursts and increased the similarity between the two recordings. The correlation coefficients increased from a mean of 0.72 at rest to 0.89 during apnoea. Coherence increased from a mean of 82.1% at rest to 91.9% during apnoea. 5. On the right side, graded voluntary contractions were performed at 5, 10, 20 or 30% maximal force using the muscle innervated by the fascicle from which the recording was made. The coherence between the recordings made from the right and left legs decreased by > 10% at each contraction level. Pooling the data for all contractions, there was a significant decrease in power at the cardiac frequency in the sympathetic recording from the contracting leg. Contraction of a synergist or antagonist at 10% maximum produced negligible changes in coherence. 6. It is concluded that, at rest, homologous muscles of the lower limbs are subject to a common drive and that, during apnoea, this common drive can dominate the sympathetic outflow to the virtual exclusion of regional drives. During voluntary activity, the importance of this common drive is lessened, presumably because of regionally specific changes involving the contracting muscle.(ABSTRACT TRUNCATED AT 400 WORDS)
Calcium‐activated potassium channels in native endothelial cells from rabbit aorta: conductance, Ca2+ sensitivity and block.
Authors: Rusko J , Tanzi F , van Breemen C , Adams D J
Published: December 2014

1. Isolated native endothelial cells, obtained by treatment of rabbit aortic endothelium with papain and dithiothreitol, were voltage clamped, and single channel (unitary) and spontaneous transient outward currents (STOCs) were recorded from both whole cells and excised membrane patches. 2. In inside‐out patches, the reversal potential of unitary currents was dependent on the extracellular K+ concentration and had a single‐channel slope conductance of 220 pS in symmetrical 140 mM‐K+ solutions. The open‐state probability (Po) of the unitary K+ currents was sensitive to the intracellular Ca2+ concentration with half‐maximal activation at approximately 1 microM at +20 mV. The ionic selectivity and Ca2+ sensitivity indicate that a large conductance, Ca(2+)‐activated K+ channel is present in freshly dissociated rabbit aortic endothelial cells. 3. The frequency and amplitude of whole‐cell unitary currents and amplitude of spontaneous transient outward currents were voltage‐dependent. Whole‐cell outward K+ currents evoked by depolarizing voltage ramps had amplitudes often corresponding to the simultaneous opening of more than five single Ca(2+)‐activated K+ channels. Lowering the intracellular EGTA concentration tenfold, and hence the Ca2+ buffering capacity of the cell, increased unitary K+ current activity and shifted the relationship between Po and membrane potential by approximately ‐20 mV. 4. Bradykinin (1 microM), adenosine 5'‐triphosphate (3 microM) and acetylcholine (3 microM) applied extracellularly evoked a biphasic increase in N Po (where N is number of channels activated) of the Ca(2+)‐activated K+ channel studied in the whole‐cell recording configuration. The development of a biphasic response to agonist stimulation requires a source of extracellular Ca2+. The sustained increase in N Po of the Ca(2+)‐activated K+ channel was attenuated upon the removal of external Ca2+ (Mg2+ replacement) or in the presence of the Ca2+ entry blocker, Ni2+, and the potassium channel blockers tetrabutylammonium (TBA) or tetraethylammonium (TEA). 5. Unitary and spontaneous transient outward currents were inhibited by extracellularly applied TEA (0.5 mM), TBA (0.5‐5 mM) and charybdotoxin (100 nM). Ca(2+)‐activated K+ currents were blocked completely by 5 mM‐TEA, whereas 3,4‐diaminopyridine (1 mM), Ba2+ (10 mM) and apamin (0.1‐1 microM) did not abolish these K+ currents. 6. The K+ channel opener cromakalim (10 microM) evoked a sustained increase in N Po of the Ca(2+)‐activated K+ channels which was not potentiated by the addition of bradykinin. Glibenclamide (10 microM) alone increased N Po and partially inhibited the cromakalim‐induced increase in N Po with respect to control.(ABSTRACT TRUNCATED AT 400 WORDS)
Monosynaptic EPSPs elicited by single interneurones and spindle afferents in trigeminal motoneurones of anaesthetized rats.
Authors: Grimwood P D , Appenteng K , Curtis J C
Published: December 2014

1. Our aim has been to quantify the monosynaptic connections of trigeminal interneurones and spindle afferents onto jaw‐elevator motoneurones as a step towards identifying common features in organization of monosynaptic inputs onto motoneurones. We have used the intracellular variant of the spike‐triggered averaging method to examine the connections of single identified trigeminal interneurones and jaw‐elevator muscle spindle afferents onto single jaw‐elevator motoneurones. The interneurones examined lay in the region immediately caudal to the trigeminal motor nucleus. The experiments were performed on rats anaesthetized with pentobarbitone, paralysed and artificially ventilated. 2. Ten EPSPs and eight IPSPs were obtained from examining the connections of seventeen interneurones to thirty‐six motoneurones, suggesting a functional connectivity of 50% for individual interneurones onto elevator motoneurones. Fourteen EPSPs were obtained from examining the connections of thirteen spindle afferents onto twenty‐seven motoneurones, giving a functional connectivity of 52% for individual spindle afferents onto elevator motoneurones. The amplitudes of the EPSPs elicited by interneurones ranged from 7‐48 microV (mean = 17, S.D. = 12.5, n = 10) and from 7 to 289 microV (mean = 64, S.D. = 76.0, n = 14) for the spindle‐mediated EPSPs; the difference in the two means was not significant (P = 0.07). 3. However, the amplitude of averaged responses obtained by signal averaging methods are dependent on the assumption that the postsynaptic response occurs following every impulse in the presynaptic neurone. We therefore estimated the percentage of sweeps which contained EPSPs triggered by the presynaptic neurone under study. In essence the method used consisted of visual inspection of the individual sweeps comprising an average in order to assess the occurrence of EPSPs within six separate time windows, each of duration +/‐ 0.3 ms. Five windows were placed at randomly selected times on average and were used to provide an estimate of the frequency of occurrence of randomly triggered EPSPs. The sixth window was centred on the start of the averaged EPSP and the frequency of occurrence of randomly triggered EPSPs was subtracted from the frequency of occurrence of EPSPs in this window to produce an estimate of the incidence of EPSPs triggered by the presynaptic neurone under study. 4. Values of the incidence of occurrence of EPSPs triggered by the presynaptic neurones ranged from 4.3 to 92% for the fifteen averaged EPSPs which could be analysed in this manner (two elicited by interneurones and thirteen by spindle afferents).(ABSTRACT TRUNCATED AT 400 WORDS)
An analysis of the long‐lasting after‐hyperpolarization of guinea‐pig vagal motoneurones.
Authors: Hocherman S D , Werman R , Yarom Y
Published: December 2014

1. The long‐lasting after‐hyperpolarization which characterizes the neurones of the dorsal motor nucleus of the vagus in the guinea‐pig was studied in vitro. 2. Following a train of action potentials, vagal motoneurones develop a long‐lasting after‐hyperpolarization. Two different shapes of long‐lasting after‐hyperpolarization were encountered: an after‐hyperpolarization which slowly (0.6‐1.2 s) and monotonically developed to peak value; and a second type of long‐lasting after‐hyperpolarization where the onset of the slow component appears to be masked by an early, relatively fast component. Both shapes of long‐lasting after‐hyperpolarization depend on Ca2+ influx and increase as a function of the number of action potentials in the train. 3. A novel procedure was used to analyse the ionic processes which underlie the long‐lasting after‐hyperpolarization. The neuronal responses to a series of long (7 s) hyperpolarizing current pulses during the long‐lasting after‐hyperpolarization were recorded and the voltage‐current curves at 600 different time points along the long‐lasting after‐hyperpolarization were plotted. The conductance and the reversal potential at each time point were calculated from the slope and the intersection of these curves, respectively. 4. Using this procedure it was found that the long‐lasting after‐hyperpolarization consists of two conductances that differ in kinetic properties and reversal potential: an early conductance which peaks shortly after the end of the train and decays in a few tenths of seconds (EAHP), and a late conductance which develops slowly (time to peak about 1 s) and decays in 3‐8 s (LAHP). The reversal potential for the early conductance is 10 mV more positive than the reversal potential for the late conductance (‐84 mV); the latter reversal potential is in agreement with the K+ equilibrium potential. The different shapes of long‐lasting after‐hyperpolarization can be explained by different ratios of these two conductances. 5. Noradrenaline (10 microM) selectively blocks the late conductance, without an observable effect on the Ca2+ action potential. 6. The behaviour of the noradrenaline‐sensitive late conductance was analysed. The amplitude of the conductance change increased sigmoidally as a function of the number of spikes in the train. A log‐log plot suggests that at least two Ca2+ ions participate in the opening of a K+ channel. 7. A model that accounts for the slow kinetics of the late conductance was constructed.(ABSTRACT TRUNCATED AT 400 WORDS)
Interactions between Ca2+ mobilizing mechanisms in cultured rat cerebellar granule cells.
Authors: Irving A J , Collingridge G L , Schofield J G
Published: December 2014

1. The interactions between IP3 receptor‐mediated and Ca(2+)‐induced Ca2+ release were investigated in cerebellar granule cell bodies, using the techniques of microfluorimetry and image analysis. 2. The IP3‐sensitive Ca2+ release mechanism was activated using acetylcholine (ACh) and the selective metabotropic glutamate receptor agonist 1‐aminocyclopentane‐1S,3R‐dicarboxylic acid (ACPD). Caffeine was used to activate, and ryanodine to inhibit, the Ca(2+)‐induced Ca2+ release process. Thapsigargin was used to deplete intracellular Ca2+ stores. 3. Transient applications of caffeine (5‐50 mM), ACPD (50‐500 microM) and ACh (0.05‐1 microM) mobilized intracellular Ca2+ ([Ca2+]i). Ca2+ mobilizing responses to 50 mM caffeine and 1 microM ACh increased with time in culture until day 4. However, beyond this period the responsiveness of cells to caffeine, but not to ACh, declined markedly. 4. Responses induced by ACPD and ACh were inhibited in the presence of caffeine at concentrations below those which mobilized Ca2+ (1‐5 mM). This effect was not due to Ca2+ pool depletion, elevation of cAMP or inhibition of phosphodiesterases. 5. Prior challenge with ACh or ACPD inhibited Ca2+ mobilization induced by caffeine (50 mM). Transient exposure to caffeine inhibited subsequent responses to ACh through a mechanism which involved store depletion. 6. Thapsigargin (0.1‐1 microM) inhibited, to a similar extent, Ca2+ mobilization induced by caffeine, ACPD and ACh. 7. Ryanodine (10 microM) antagonized Ca2+ mobilization induced by caffeine, ACh and ACPD. However, the ability of ryanodine to block inositol 1,4,5‐trisphosphate‐linked agonist responses varied considerably between cells. The sensitivity of ACh‐induced responses to ryanodine correlated with the sensitivity of the cells to caffeine. 8. The possible explanations for the pronounced interactions between IP3 receptor‐mediated and Ca(2+)‐induced Ca2+ release processes in cerebellar granule cells are discussed.
Dynamic changes in human diaphragm length: maximal inspiratory and expulsive efforts studied with sequential radiography.
Authors: Gandevia S C , Gorman R B , McKenzie D K , Southon F C
Published: December 2014

1. The maximal voluntary pressure generated by the diaphragm (transdiaphragmatic pressure, Pdi) is about 50% greater during maximal expulsive efforts than during maximal inspiratory efforts against a closed airway. However, these pressures cannot be increased by interpolated phrenic stimuli in trained subjects. This suggests that variable neural drive is not responsible for the difference in voluntary pressure. To investigate whether dynamic changes in diaphragm length during inspiratory and expulsive efforts could account for this difference, we used digital sequential radiography at 6 frames per second. 2. During the development of peak Pdi in inspiratory efforts, total diaphragm length decreased by about 20% in the antero‐posterior and lateral projections. During maximal expulsive efforts (with glottis open), the diaphragm shortened slightly in the early stage of pressure development but then lengthened due to contraction of abdominal muscles before peak pressure was achieved. 3. Given that force increases when a contracting muscle is lengthened (expulsive effort) and decreases during shortening (inspiratory effort), this study provides a definitive explanation for the difference in maximal voluntary pressure between pure inspiratory and expulsive efforts.
Effect of nitro‐L‐arginine on endothelium‐dependent hyperpolarizations and relaxations of pig coronary arteries.
Authors: Pacicca C , von der Weid P Y , Beny J L
Published: December 2014

1. Endothelium‐dependent relaxation is caused by an endothelium‐derived relaxing factor (EDRF) identified as nitric oxide (NO). Our objective was to test whether one or several distinct endothelium‐dependent relaxing factors exist. 2. In pig coronary arteries, a hyperpolarization accompanied by the relaxation caused by high concentrations of substance P (SP) and bradykinin (BK). 3. To examine the role played by nitric oxide and prostacyclin in the endothelium‐dependent relaxations and hyperpolarizations caused by SP and BK on pig coronary arterial strips, the production of NO was inhibited by NG‐nitro‐L‐arginine (L‐NNA) and the production of prostacyclin was inhibited by indomethacin, while monitoring smooth muscle membrane potential and isometric tension. 4. Indomethacin had no effect on resting isometric tension nor on SP and BK relaxations of strips precontracted by prostaglandin F2 alpha. 5. L‐NNA contracted arterial strips with intact endothelium, without changing the membrane potential of smooth muscles. 6. The inhibitor shifted to the right the concentration‐response curve of kinins by 0.2 nM SP and 20 nM BK. It inhibited the maximal relaxations and hyperpolarizations by 30%. 7. The results show that, in pig coronary arteries, EDRF (NO) mainly controls the basal tension, whereas other factor(s) play(s) an important role in hyperpolarizations and relaxations caused by the kinins.
Respiratory‐related activity patterns in preganglionic neurones projecting into the cat cervical sympathetic trunk.
Authors: Boczek‐Funcke A , Dembowsky K , Häbler H J , Jänig W , Michaelis M
Published: December 2014

1. Activity in 233 single sympathetic preganglionic neurones that project to the superior cervical ganglion was analysed with respect to central components of respiration (phrenic nerve discharge) and to the afferent feedback generated by mechanical events occurring with ventilation in anaesthetized and artificially ventilated cats. 2. The activity in ninety‐one neurones was modulated during the respiratory cycle in two ways: directly by the central inspiratory drive, and indirectly by ventilation‐related blood pressure changes, acting via the systemic baroreceptors. The direct influence was prominent in vagotomized animals or those with a raised respiratory drive, and consisted of an inspiratory increase in activity and decreases of activity in early inspiration and postinspiration. The indirect influence (excitation due to baroreceptor unloading) usually dominated in normocapnic cats with intact vagus nerves. This population of neurones showed both similar reflex responses and a similar respiratory modulation of activity as postganglionic neurones supplying hindlimb skeletal muscle. 3. Sixty‐one neurones discharged exclusively, or almost exclusively, during central inspiration. This discharge pattern neither depended on the integrity of vagal nor baroreceptor afferents. The activity of these neurones was abolished during hyperventilation and enhanced during hypercapnia. In the latter state, a small activation was often seen in stage II expiration. 4. In normocapnia the remainder of neurones (n = 81) exhibited no, or no pronounced, respiratory modulation of activity, except three neurones which showed a prominent expiratory pattern being of central and not of reflex origin. They were not a homogeneous population and included neurones exhibiting reflex responses similar to those of postganglionic neurones supplying hindlimb skin (n = 36), neurones responding to light (n = 4), and others (n = 41). 5. It is concluded that distinct types of thoracic preganglionic neurone differ with respect to respiratory modulation of their activity stemming from both central and reflex sources. Thus, the temporal profile of activity in these neurones in relation to respiration is another functional characteristic which can be used to distinguish between populations of sympathetic neurones.
Asymmetry of vascular responses of perfused rabbit carotid artery to intraluminal and abluminal vasoactive stimuli.
Authors: Kaul S , Waack B J , Heistad D D
Published: December 2014

1. Responses of the carotid artery of rabbits to intraluminal and abluminal administration of purinergic agonists were examined. The carotid artery was perfused in vitro and changes in diameter were recorded. 2. Intraluminal acetylcholine, ADP, and ATP produced pronounced vasodilatation, whereas abluminal acetylcholine, but not ADP and ATP, produced dilatation of phenylephrine‐preconstricted arteries. Intra‐ and abluminal adenosine and nitroprusside produced equipotent vasodilatation. 3. N omega‐nitro‐L‐arginine abolished dilator responses to acetylcholine and adenine nucleotides, and unmasked vasoconstrictor responses to high concentrations of these agonists. Responses to adenosine and nitroprusside were not affected by nitro‐L‐arginine. 4. Intraluminal, but not abluminal, administration of nucleotidase‐resistant adenine nucleotide analogues 2‐methylthio‐ATP and ADP beta S produced significant vasodilation in arteries preconstricted with phenylephrine. Intra‐ and abluminal administration of alpha,beta‐methylene‐ATP, a potent P2X‐purinoceptor agonist, did not produce vasodilatation in preconstricted arteries. 5. Abluminal ADP failed to elicit dilatation of phenylephrine‐preconstricted arteries even in the presence of the ADPase inhibitor beta,gamma‐methylene‐ATP (10(‐5)M). When P2X‐purinoceptors, which mediate adenine nucleotide‐induced vasoconstriction, were stimulated with alpha,beta‐methylene‐ATP (10(‐5)M), abluminal ADP produced vasodilatation, presumably because P2X‐purinoceptors were occupied, thereby unmasking P2Y‐purinoceptor‐mediated dilatation. 6. These results suggest that asymmetric vascular responses of rabbit carotid arteries to adenine nucleotides may be due in part to preferential activation of P2Y‐purinergic receptors on endothelium and P2X‐purinergic receptors on vascular smooth muscle.
Effect of catecholamines on intracellular pH in sheep cardiac Purkinje fibres.
Authors: Guo H , Wasserstrom J A , Rosenthal J E
Published: December 2014

1. It has been reported that catecholamines affect intracellular pH (pHi) in a number of tissues, generally by altering the kinetics of the Na(+)‐H+ exchanger. We postulated that catecholamines might affect pHi in cardiac tissue. We tested this in resting sheep cardiac Purkinje fibres by measuring transmembrane potential and pHi with standard and H(+)‐sensitive microelectrodes. 2. Adrenaline and the beta‐adrenergic agonist isoprenaline, both 5.0 x 10(‐6) M, resulted in depolarization and intracellular acidification (adrenaline, 0.03 +/‐ 0.01 pH units, n = 8, P = 0.005; isoprenaline, 0.08 +/‐ 0.01 pH units, n = 17, P = 0.0001). The alpha‐adrenergic agonist phenylephrine, at concentrations up to 200 microM, had no significant effect on membrane potential or pHi. 3. Isoprenaline significantly attenuated the half‐time (t0.5) for pHi recovery from intracellular acidification induced via the NH4Cl pulse technique. Isoprenaline also attenuated the hyperpolarization that is normally seen at the onset of pHi recovery. Phenylephrine slightly reduced the t0.5 for recovery, although the reduction did not reach statistical significance. 4. Forskolin, 7.5‐10 x 10(‐5) M, an agent that raises intracellular cyclic adenosine 3',5'‐monophosphate (cyclic AMP), also induced depolarization and acidification, similar to that induced by adrenaline and isoprenaline. 5. In the presence of the Na(+)‐H+ exchange blocker 5‐dimethyl amiloride, 2‐6 x 10(‐5) M, isoprenaline‐induced acidification was blunted but not abolished. When administered in Na(+)‐free Tyrode solution, isoprenaline‐induced acidification was also not abolished. Buffering power, tested using the NH4Cl method, was not decreased by isoprenaline, but rather, was slightly increased. Reversal of H+ driving force across the cell membrane from the normally inward direction to outward (achieved by increasing pHo to 8.3‐8.5 and depolarizing the membrane with 10 mM K+ solutions) did not prevent intracellular acidification from occurring in the presence of isoprenaline. When glycolysis was inhibited by a 60 min exposure to glucose‐free solution containing 5.5 mM 2‐deoxyglucose, acidification by isoprenaline was nearly abolished. 6. We conclude that, in resting sheep Purkinje fibres, beta‐ but not alpha‐adrenergic stimulation results in intracellular acidification and depolarization, probably mediated via an increase in cyclic AMP. beta‐ but not alpha‐adrenergic stimulation slows the rate of recovery from intracellular acidification and blunts the hyperpolarization associated with this recovery. 7. The intracellular acidification appears to be due both to partial inhibition of Na(+)‐H+ exchange and to stimulation of glycolysis by beta‐adrenergic agents.
Discharge characteristics and rapid resetting of autoactive aortic baroreceptors in rats.
Authors: Munch P A
Published: December 2014

1. An in vitro aortic arch‐aortic nerve preparation was used to characterize the pressure‐discharge properties of aortic ‘autoactive’ baroreceptors (aBRs), a functionally unique group of baroreceptors that discharge continuously below pressure threshold (Pth). These units contrast to more familiar ‘quiescent’ BRs (qBRs) that are silent below Pth. This study also examined whether aBRs rapidly reset to sustained changes in mean arterial pressure (MAP), and whether they respond to local vasoconstriction, as found in qBRs. 2. Pressure‐discharge curves were constructed using slow pressure ramps (2 mmHg s‐1) in a total of fifty‐four aBRs and sixty‐four qBRs from fifty‐three Wistar‐Kyoto rats. Rapid resetting was tested by comparing the curves before and 15 min after adjusting MAP to selected levels between 40 and 180 mmHg. Response curves were also compared before and after constricting the arch with 10(‐8) M angiotensin II. 3. Compared to qBRs, aBRs had significantly lower Pth values (83 +/‐ 2 versus 91 +/‐ 2 mmHg, mean +/‐ S.E.M., P < 0.05) but similar threshold frequencies (13 +/‐ 1 versus 16 +/‐ 2 Hz), higher saturation pressures (138 +/‐ 4 versus 123 +/‐ 2 mmHg) but similar saturation frequencies (55 +/‐ 3 versus 55 +/‐ 3 Hz), and lower suprathreshold sensitivities (slope of linear region: 1.1 +/‐ 0.1 versus 1.4 +/‐ 0.1 Hz mmHg‐1) but wider operating ranges (57 +/‐ 4 versus 35 +/‐ 3 mmHg). 4. The aBRs rapidly reset to changes in MAP (n = 16), and the extent of resetting (delta Pth/delta MAP = 0.26) was similar to that in qBRs (0.23). 5. Vasoconstriction had no effect on aBR subthreshold discharge (n = 5), but inhibited suprathreshold responses to pressure much like that in qBRs. 6. These results suggest that aortic aBRs may extend the range of the baroreflex, but probably do not improve its sensitivity to transient fluctuations in pressure or its ability to correct changes in mean pressure over extended periods. 7. Subthreshold discharge in aBRs appears to be an intrinsic property of these units, which was not affected by resetting or changes in vascular tone. At suprathreshold pressures, contraction of local smooth muscle modulates the aBRs and qBRs in a similar fashion by mechanically unloading the sensory endings.
The whole‐cell calcium current in acutely dissociated magnocellular cholinergic basal forebrain neurones of the rat.
Authors: Allen T G , Sim J A , Brown D A
Published: December 2014

1. The electrophysiological and pharmacological characteristics of the calcium current (ICa) in acutely dissociated magnocellular cholinergic basal forebrain neurones from 11‐ to 14‐day‐old post‐natal rats were studied using the whole‐cell patch‐clamp technique. 2. All cells exhibited a small transient low‐voltage‐activated (LVA) current with half‐activation and half‐inactivation potentials of ‐40.2 and ‐49.3 mV and slope factors for activation and inactivation of 4.82 and 3.85 mV per e‐fold change in membrane potential (Vm) respectively. Activation and inactivation rates for the LVA current were highly voltage dependent. For test potential changes from ‐50 to ‐20 mV, the time‐to‐peak of the current decreased from 39.1 to 6.4 ms, and the time constant of current decay decreased from 81.7 to 15.5 ms. 3. A high‐voltage‐activated (HVA) component of ICa could be elicited at threshold voltages between ‐46 and ‐30 mV from a holding potential (VH) of ‐80 mV. The HVA current peaked around 0 mV; a 10‐fold increase in [Ca2+]o produced a 13 mV positive shift in the peak, whilst the amplitude of the current showed an approximately hyperbolic relationship to [Ca2+]o with half‐saturation at 2.5 mM. The transient phase of the HVA current could be described by two exponential functions with time constants tau fast and tau slow of 16.2 and 301 ms. Steady‐state inactivation of the transient and extrapolated true sustained (pedestal) components of HVA current were described by Boltzmann equations, with half‐inactivation potentials (slope factors) of ‐47.3 mV, (9.04) and ‐29.2 mV (11.8) respectively. 4. omega‐Conotoxin (omega‐CgTX; 100 nM) irreversibly inhibited a kinetically distinct component of HVA current but had no effect upon the transient LVA current. The omega‐CgTX‐sensitive current could not be distinguished from the control HVA current by the voltage dependence of its activation or inactivation rates. 5. Low concentrations of amiloride (< or = 300 microM) or Ni2+ (< or = 5 microM) selectively inhibited the transient LVA current, with IC50 values of 97 and 5 microM respectively. Cd2+ (< or = 1 microM) selectively blocked a component of HVA current. At higher concentrations, Cd2+ and Ni2+ were non‐selective and totally blocked all components of ICa. 6. The lanthanide ions Gd3+ and La3+ produced saturable incomplete block of the HVA current. Maximally effective concentrations of Gd3+ (100 microM) or La3+ (30 microM) inhibited 76.5 and 41.2% respectively of the sustained component of HVA current with corresponding IC50 values of 2.2 and 1.1 microM.(ABSTRACT TRUNCATED AT 400 WORDS)