bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of non‐quantal acetylcholine release in surplus polarization of mouse diaphragm fibres at the endplate zone.
Authors: Nikolsky E E , Zemková H , Voronin V A , Vyskocil F
Published: December 2014

1. In mouse diaphragm, with intact cholinesterase (ChE), the mean value of the resting membrane potential was significantly higher (‐84.8 +/‐ 0.3 mV; mean +/‐ S.E.M.) at the endplate zone than in the extrajunctional area of the muscle fibres (‐82.5 +/‐ 0.3 mV) at 22 degrees C. 2. This hyperpolarization of about 2‐3 mV at the endplate zone was abolished within 5 min by 1 x 10(‐6) M ouabain, indicating that it might be caused by an electrogenic Na(+)‐K+ pump. (+)‐Tubocurarine (TC; 1 x 10(‐5) M) had no effect on this hyperpolarization after bath application for 10‐20 min. 3. Short‐term denervation (4 h), a slight increase of Mg2+ in the bath of from 1 to 4 mM and application of a Ca(2+)‐free solution for 60 min also led to the disappearance of the surplus polarization. All of these factors are known to eliminate TC‐induced hyperpolarization in anti‐ChE‐treated muscles (H‐effect), which is considered to be a correlate of non‐quantal acetylcholine (ACh) leakage. 4. The time courses of the decline of the H‐effect and surplus polarization after denervation were identical. 5. In short‐term denervated muscles with intact ChE, the surplus polarization was restored by 5 x 10(‐8) M ACh, which simulates the H‐effect in anti‐ChE‐treated muscles. The presence of 1 x 10(‐6) M ouabain either prevented or abolished the effect of the bath‐applied ACh.(ABSTRACT TRUNCATED AT 250 WORDS)
Quantal nature of synaptic transmission at the cytoneural junction in the frog labyrinth.
Authors: Rossi M L , Martini M , Pelucchi B , Fesce R
Published: December 2014

1. The mechanism of transmitter release at the cytoneural junction of the frog posterior canal was investigated by recording intracellularly subthreshold postsynaptic potentials (EPSPs), and performing a statistical analysis of time intervals and peak amplitudes. In single units EPSPs display highly variable size, so it is not clear whether they are generated by the release of single quanta of transmitter and whether large ones represent giant events, multiquantal events, or the random summation of independent unitary events. 2. In units with low resting EPSP rates, peak amplitudes and time intervals between EPSPs were measured directly. Peak amplitude histograms were continuous, unimodal and well fitted by log normal distributions. Time‐interval histograms were well described by single exponentials. 3. At high EPSP rates (either at rest or during experimental treatments), where single events overlapped extensively, peak amplitude histograms were skewed markedly towards high values. Under these conditions, the EPSP waveform was estimated by autoregressive fit to the autocorrelation of the recorded signal. The fit was used to build a Wiener filter, for sharpening the original signal, before computing time‐interval and peak amplitude histograms. This yielded consistent log normal peak amplitude distributions with no ‘excess’ skewness, similar to those obtained with low resting rates. 4. After sharpening by the Wiener filter, shoulders or small second peaks in amplitude distributions were observed only at the highest EPSP rates (> 300 s‐1). The number of ‘multiquantal’ events was reduced by Wiener filtering, and was in general consistent with the expectation that more than one independent event occurred within the duration of the single event. This suggests that the events are uniquantal, random and independent, i.e. miniature EPSPs (mEPSPs). 5. In general, peak amplitude distributions obtained with modified external Ca2+ concentration ([Ca2+]o) and/or during mechanical stimulation or under efferent activation were not significantly altered with respect to those obtained in the same units at rest. Time‐interval histograms were generally mono‐exponential at rest as well as during mechanical or efferent stimulation, and irrespective of [Ca2+]o. Resting mEPSP rate was slightly increased by elevated [Ca2+]o and reduced by low [Ca2+]o. The increase in mEPSP rate produced by mechanical excitation was depressed by both high and low [Ca2+]o, whereas both conditions enhanced mechanical inhibition. Efferent inhibition was little affected. High [Ca2+]o hastened adaptation during efferent facilitation. Low [Ca2+]o reduced peak response during facilitation, but suppressed its warning. 6. In the presence of ATP a consistent though transient increase in resting mEPSP rate was observed in about 50% of units.(ABSTRACT TRUNCATED AT 400 WORDS)
A study of the action of bradykinin and bradykinin analogues in the human nasal airway.
Authors: Austin C E , Foreman J C
Published: December 2014

1. The aim of this study was to investigate the action of bradykinin on resistance to airflow and on vascular permeability in the human nasal airway, and to explore the receptor mediating these effects. 2. Aerosol administration of bradykinin (10‐1000 micrograms) caused a dose‐related increase in nasal airway resistance (NAR) and an increase in albumin content of nasal lavage. 3. The bradykinin antagonists, [1‐adamantane acetyl‐D‐Arg0, Hyp3, Thi5,8, D‐Phe7]‐bradykinin, 100 micrograms, and [D‐Arg0, Hyp3, Thi5, D‐Tic7, Oic8]‐bradykinin, 100 micrograms, given 2 min before bradykinin, inhibited the increase in NAR and the increase of albumin content of nasal lavage caused by bradykinin. 4. The bradykinin antagonist, [D‐Arg0, Hyp3, D‐Phe7]‐bradykinin (100 micrograms) did not affect the increase in NAR produced by bradykinin, or the albumin content of nasal lavage. Increasing the dose of the antagonist to 1000 micrograms did not change the increase in NAR induced by bradykinin. 5. The selective B1 kinin receptor agonist, [Des‐Arg10]‐kallidin (100 micrograms) did not affect NAR or the albumin content of nasal lavage. 6. The receptor mediating increased NAR and the release of albumin induced by bradykinin in the human nasal airway appears not to be a B1 kinin receptor. The data are not entirely consistent with the effects of bradykinin in the human nasal airway being mediated by a B2 kinin receptor.
Swelling‐induced anion and cation conductances in human epididymal cells.
Authors: Chan H C , Fu W O , Chung Y W , Huang S J , Chan P S , Wong P Y
Published: December 2014

1. Activation of both anion and cation conductances was observed in primary cultured human epididymal cells during osmotic swelling under the patch‐clamp whole‐cell configuration. The swelling‐induced anion conductance was 25.66 +/‐ 4.70 nS and the cation conductance was 7.35 +/‐ 1.40 nS. The permeability ratio of K+ to Cl‐ (PK/PCl) was calculated to be 0.40. Known anion or cation channel blockers could inhibit both conductances simultaneously. 2. When the major permeant ion species in the pipette and bath solution was Cl‐, the mean conductance was found to be 17.06 +/‐ 1.8 nS, significantly smaller than that obtained in the presence of intracellular K+, 25.66 +/‐ 4.70 nS (P < 0.05). No significant current activation was observed when solutions containing only K+ as the permeant ion were used. 3. When the anionic amino acids glutamate and aspartate were used to replace extracellular Cl‐, the permeability ratios were calculated to be PGlut/PCl = 0.20 and PAsp/PCl = 0.17. 4. The cation conductance was found to be non‐selective since its permeability to other cations such as Na+ and choline, an organic compound highly concentrated in epididymal fluid, was similar to that of K+. 5. Regulatory volume decrease (RVD) was observed after initial osmotic swelling; this could be inhibited by either anion or cation channel blockers. 6. The results of this study suggest that both anion and cation conductances are activated during cellular swelling, and indicate the existence of an interdependent relationship between the swelling‐induced cation and anion conductances. Both swelling‐induced cation and anion conductances are involved in the volume regulatory process and may be responsible for transporting amino acids or organic compounds in human epididymal cells.
Origin of delayed outward ionic current in charge movement traces from frog skeletal muscle.
Authors: Hui C S , Chen W
Published: December 2014

1. Non‐linear membrane ionic current was studied in highly stretched cut frog twitch fibres in a double Vaseline‐gap voltage clamp chamber, with the internal solution containing 0.1 mM EGTA and the external solution containing Cl‐ as the major anion. After the Na+ currents was abolished by TTX in the external solution and the K+ currents were suppressed by external TEA+ and Rb+ and internal Cs+, a delayed outward ionic current with a time course similar to that of the delayed rectifier current was observed during depolarization. 2. The delayed outward ionic current was resistant to 1 mM 3,4‐diaminopyridine (3,4‐DAP) in the external solution and was unaltered when a fraction of the internal Cs+ was replaced by K+ or Na+, suggesting that the current was not carried by cations flowing through the delayed rectifiers. 3. The delayed outward ionic current was greatly reduced by replacing the external Cl‐ with CH3SO3‐,SO4(2‐), glutamate or gluconate, indicating strongly that the current was carried by Cl‐ flowing through anion channels. The current was also suppressed by 1 mM external 9‐anthracenecarboxylic acid (9‐ACA). 4. The delayed outward ionic current was reduced by blockers of calcium‐dependent Cl‐ channels, such as SITS and frusemide (furosemide), in a dose‐ and voltage‐dependent manner and by increasing intracellular [EGTA] to 20 mM, suggesting that part of the Cl‐ current in the muscle fibres could be calcium dependent. 5. The total Cl‐ current could be dissected into calcium‐dependent and calcium‐independent components. Each component accounted for roughly half of the total Cl‐ current. The maximum slope conductance of the calcium‐dependent Cl‐ channels was 60.9 +/‐ 6.0 microS microF‐1 (mean +/‐ S.E.M., n = 4).
A novel voltage‐dependent cation current in rat neocortical neurones.
Authors: Alzheimer C
Published: December 2014

1. Using the whole‐cell configuration of the patch‐clamp technique, an unexpected voltage‐dependent cation current (Icat) was recorded from acutely isolated rat neocortical neurones, the Na+, K+ and Ca2+ currents of which were pharmacologically suppressed. 2. Icat was activated at potentials more positive than ‐45 mV, displayed outward rectification, and deactivated with a slow voltage‐dependent time course causing prominent inward tail currents. 3. Activation of Icat was not dependent on Ca2+ influx or increases in cytosolic Ca2+, since it was not abolished by inorganic Ca2+ channel blockers or by internal Ca2+ chelators. 4. Icat was reduced by tetraethylammonium at high concentrations, but not by 4‐amino‐pyridine, and proved to be insensitive to cation channel blockers such as Cs+, amiloride or gadolinium. 5. Ion substitution experiments revealed that the channel producing Icat was permeable to a number of monovalent cations, including K+, Cs+, Na+ and choline+, but not to the Cl‐anion. 6. The features of Icat suggest that, in electrically active neurones, it should play a role in both the initial repolarization of membrane potential after strong depolarization and the generation of depolarizing after‐potential.
Effect of arterial‐portal glucose gradients and phloridzin on bile glucose levels in perfused rat liver.
Authors: Crafer S M , Pryor J S , Dawson A P
Published: December 2014

1. Bivascular perfused rat liver was used to study the effects of hepatic artery‐portal vein glucose gradients and the effects of phloridzin on bile glucose levels. 2. Bile glucose levels were examined when glucose concentrations in the hepatic artery (HA) and portal vein (PV) inflows were equal. When the concentration of perfusate glucose was 10 mM, bile glucose remained stable at less than 0.075 mM; when perfusate glucose exceeded approximately 16.0 mM, bile glucose increased rapidly; when 1.6 microM phloridzin and 10.0 mM glucose were co‐infused, phloridzin entered rapidly into bile and settled at a steady‐state concentration of 0.45 +/‐ 0.04 mM, and bile glucose increased to 3.75 +/‐ 0.14 mM. 3. During perfusion of HA‐PV glucose gradients such that HA glucose was higher than that in the sinusoids, bile glucose levels were increased compared with their levels when HA glucose was equivalent to that in the sinusoids. The converse was also demonstrated. 4. The results regarding phloridzin‐sensitive glucose transport in the biliary tree of the rat were consistent with those documented in vivo. The finding that bile glucose levels altered in a manner parallel to that of the HA, although the total inflow remained unchanged, strongly indicated that HA glucose level, rather than that of the PV, performs an important role in control of bile glucose levels.
Regulation of intracellular pH in the smooth muscle of guinea‐pig ureter: Na+ dependence.
Authors: Aickin C C
Published: December 2014

1. Mechanisms involved in the regulation of intracellular pH (pHi) in smooth muscle cells of guinea‐pig ureter have been investigated using double‐barrelled pH‐sensitive microelectrodes in isolated strips of tissue. 2. Removal of CO2‐HCO3‐ from the superfusing solution caused a fall in the steady‐state pHi except in a few cells which had been excised from the animal for many hours (usually > 24 h). The pHi value was 7.22 +/‐ 0.09 (n = 89; mean +/‐ S.D. of an observation) in solution buffered with 5% CO2‐21 mM HCO3‐, compared with 6.92 +/‐ 0.24 (n = 67) in the nominal absence of CO2‐HCO3‐. Recovery from experimentally induced acidosis was faster in the presence, rather than nominal absence, of CO2‐HCO3‐ (mean half‐times of 2.7 +/‐ 0.7 min, n = 41, and 4.6 +/‐ 1.3 min, n = 12, respectively). These results suggest the presence of both HCO(3‐)‐dependent and ‐independent mechanisms for the effective extrusion of acid equivalents. 3. Recovery from acidosis was dependent on external Na+ (Na+o) in both the presence and nominal absence of CO2‐HCO3‐, with an apparent half‐maximal activation at approximately 4 and 20 mM Na+o, respectively. Removal of Na+o in the steady state caused a fall in pHi which proceeded at a faster rate in the presence rather than in the nominal absence of CO2‐HCO3‐. 4. Amiloride (100 microM‐1 mM) reversibly inhibited the recovery from acidosis and caused a fall in the steady‐state pHi when applied in the nominal absence of CO2‐HCO3‐, but had no measurable effect on either the recovery from acidosis or steady‐state pHi in the presence of CO2‐HCO3‐. These results suggest that Na(+)‐H+ exchange was responsible for extrusion of acid equivalents in the nominal absence of CO2 and HCO3‐, but that it played little part under more physiological conditions. 5. Although Na(+)‐H+ exchange appeared to be activated below a pHi of about 7.2, it was incapable of maintaining a ‘normal’ pHi in the nominal absence of CO2‐HCO3‐ in freshly excised cells, where values between 6.06 and 6.89 were recorded. Only in aged preparations, in which the intrinsic intracellular acid loading was substantially reduced (as judged from the rate of acidification on application of amiloride in the nominal absence of CO2‐HCO3‐) did the steady‐state value approximate to that observed in the presence of CO2‐HCO3‐, at about 7.2.
Segmental differences in the effects of guanylin and Escherichia coli heat‐stable enterotoxin on Cl‐ secretion in human gut.
Authors: Kuhn M , Adermann K , Jähne J , Forssmann W G , Rechkemmer G
Published: December 2014

1. Mucosally added synthetic guanylin and Escherichia coli heat‐stable enterotoxin (STa) increased short‐circuit current (ISC) across isolated muscle‐stripped human intestine in vitro. 2. Serosal bumetanide inhibited ISC responses indicating that guanylin and STa stimulate electrogenic chloride secretion. 3. ISC responses were markedly greater in the colon than in the jejunum. 4. Pretreatment with indomethacin did not significantly alter the effects of guanylin and STa. 5. Both peptides induced concentration‐dependent increases in the cyclic GMP content of human intestinal mucosa in vitro; cyclic AMP levels remained unchanged. 6. In contrast to ISC responses, increases in cyclic GMP content induced by guanylin and STa were markedly greater in the jejunum than in the colon. 7. Sodium nitroprusside (SNP) but not human alpha‐atrial natriuratic peptide (CDD/ANP(99‐126)) increased chloride secretion in human intestine; both agents induced small increases in intestinal cyclic GMP content. 8. Guanylin, STa and the nitric oxide (NO) donor SNP increased electrogenic chloride secretion across human intestinal mucosa in vitro by stimulation of cyclic GMP. The discrepancy between the effects on chloride secretion and intracellular cyclic GMP content suggest different cellular action sites of guanylin and STa in human small and large intestine.
M1 muscarinic receptor‐mediated facilitation of acetylcholine release in the rat urinary bladder.
Authors: Somogyi G T , Tanowitz M , de Groat W C
Published: December 2014

1. Release of [3H]ACh in response to electrical field stimulation (10 Hz) was measured in strips of rat urinary bladder and cardiac atrial tissues previously incubated with [3H]choline. 2. The volley output of [3H]ACh release was positively correlated with frequency of stimulation in the urinary bladder but negatively correlated in the atrium. 3. The quantity of [3H]ACh release was influenced by the pattern and duration of stimulation. Continuous stimulation (CS) with trains of 100 shocks released 10 times larger amounts of ACh than the same number of shocks presented as short trains of intermittent stimulation (IS): ten shocks per train with 5 s inter‐train intervals. 4. The facilitation of transmitter release was antagonized completely by the administration of atropine (1 microM) or pirenzepine (0.05 microM), a selective M1 antagonist. Eserine, an anticholinesterase agent, markedly facilitated ACh release induced by CS and IS. This effect was blocked by atropine. 5. Release of ACh from atrial strips did not exhibit CS‐induced facilitation. Eserine decreased IS‐ and CS‐evoked ACh release in the atrium. 6. It is concluded that continuous stimulation of postganglionic cholinergic nerves in the rat urinary bladder leads to the activation of M1 muscarinic, facilitatory presynaptic receptors which enhance the release of ACh. Presynaptic facilitation may be an important mechanism for modulating neural input to the bladder during micturition.
Bleached pigment activates transduction in isolated rods of the salamander retina.
Authors: Cornwall M C , Fain G L
Published: December 2014

1. We have used suction electrode recording together with rapid steps into Li+ solution and 0.5 mM IBMX solution to estimate the rates of the guanylyl phosphodiesterase (PDE) and guanylyl cyclase in isolated rods of the salamander, Ambystoma tigrinum. 2. We show that both the PDE and cyclase velocities are accelerated by steady background light. The steady velocities of both enzymes appear to be saturating functions of background intensity. 3. Bleaching also accelerates both the PDE and cyclase. This effect is maintained long after the bleaching stimulus is removed (up to 2 h) and is reversed only if the photopigment is regenerated with exogenous chromophore. 4. The estimated steady‐state PDE and cyclase velocities appear to be linear functions of the amount of pigment bleached, as if each bleached pigment molecule activated the transduction cascade with the same probability and gain. 5. The effectiveness of bleached pigment in activating transduction is only 10(‐6) to 10(‐7) times that of activated rhodopsin (Rh*), but this is sufficient after large bleaches to produce an ‘equivalent background’ excitation of the rod, which is probably responsible, at least in part, for bleaching desensitization.
Evidence that glial cells modulate extracellular pH transients induced by neuronal activity in the leech central nervous system.
Authors: Rose C R , Deitmer J W
Published: December 2014

1. The role of the giant neuropile glial cells in the buffering of activity‐related extracellular pH changes was studied in segmental ganglia of the leech Hirudo medicinalis L. using pH‐sensitive microelectrodes and a slow, two‐electrode voltage‐clamp system. Neuronal activity was induced by electrical stimulation of a ganglionic side nerve (20 Hz, 1 min). 2. In CO2‐HCO3(‐)‐buffered saline the glial cells were depolarized by 6.5 +/‐ 2.3 mV and alkalinized by 0.024 +/‐ 0.006 pH units (mean +/‐ SD) during the stimulation. The stimulation induced an acidification of 0.032 +/‐ 0.006 pH units in the extracellular spaces (ECS). 3. Voltage clamping the glial cells suppressed the stimulus‐induced glial depolarization and turned the intraglial alkalinization into an acidification of 0.045 +/‐ 0.021 pH units (n = 6) that closely resembled the acidification observed in the presence of the anion transport blocker DIDS (4,4'‐diisothiocyanatostilbene‐2,2'‐disulphonic acid, 0.5 mM), and in CO2‐HCO(3‐)‐free saline. 4. Voltage clamping the glial cell resulted in the appearance of a distinct stimulus‐induced extracellular alkalinization of 0.024 +/‐ 0.013 pH units at the onset of the stimulation, as also observed during DIDS application and in the absence of CO2‐HCO3‐. 5. The results suggest that glial uptake of bicarbonate is mediated by depolarization‐induced activation of the electrogenic Na(+)‐HCO3‐ cotransport, which suppresses the profound alkalinization of the ECS during neuronal activity. This is the first direct evidence the glial cells actively modulate extracellular pH changes in a voltage‐dependent manner.
Nitric oxide modulation of quantal secretion in chick ciliary ganglia.
Authors: Lin Y Q , Bennett M R
Published: December 2014

1. Long‐term potentiation of quantal secretion was studied at ciliary ganglion synapses of post‐hatched birds following tetanic stimulation of the oculomotor nerve and the effects of nitric oxide (NO) on quantal secretion were determined. 2. Tetanic stimulation of the oculomotor nerve at 30 Hz for 20 s at room temperature increased the amplitude of the excitatory postsynaptic potential (EPSP) by about 100%; 1‐2 min after the tetanus the EPSP declined exponentially with a time constant of about 10 min (long‐term potentiation; LTP). LTP was due to an increase in the quantal content of the EPSP not to a change in quantal size. 3. A component of LTP was shown to be due to the release of NO in the ganglion, as blocking the synthesis of NO with L‐arginine methyl ester decreased the potentiation by 70%. 4. Exogenous application of NO using sodium nitroprusside increased the amplitude of the EPSP by more than 30% due to an increase in the quantal content of the EPSP. 5. Both 8‐bromo‐cGMP and 8‐bromo‐cAMP increased the quantal content of the EPSP by more than 44% without changing the quantal size. 6. The results suggest that endogenous NO is involved in either the initiation or maintenance phase of LTP. This may occur through an increase in quantal secretion consequent on the action of an elevated cGMP increasing cAMP.
The energy expenditure of actomyosin‐ATPase, Ca(2+)‐ATPase and Na+,K(+)‐ATPase in guinea‐pig cardiac ventricular muscle.
Authors: Schramm M , Klieber H G , Daut J
Published: December 2014

1. The rate of heat production (heat rate) and isometric twitch tension of ventricular trabeculae isolated from guinea‐pig heart were measured at 37 degrees C in order to determine the relative contributions of actomyosin‐ATPase, Ca(2+)‐ATPase and Na+,K(+)‐ATPase to myocardial energy metabolism. 2. The increase in heat rate recorded during isometric contractions at optimal length (contraction‐related heat production) was 19.1 +/‐ 1.2 mW cm‐3 at a stimulation rate of 2 Hz. The tension‐time integral of individual contractions measured under the same conditions was 147 +/‐ 15 mM s cm‐2. 3. The heat production of the actomyosin‐ATPase was determined by inhibiting the contractile proteins with 2,3‐butanedione monoxime (BDM). Contraction‐related heat production was reduced by 0.219 +/‐ 0.010 and the isometric tension‐time integral was reduced by 0.288 +/‐ 0.016 in the presence of 1 mM BDM. From these data an estimate of 0.76 for the relative contribution of the actomyosin‐ATPase to contraction‐related heat production was derived. 4. The heat production related to actomyosin‐ATPase plus Ca(2+)‐ATPase was studied by blocking Ca2+ influx into the myocardial cells with a solution containing 100 microM Ca2+ and 400 microM Ni2+. In this solution contraction‐related heat production was reduced by 0.907 +/‐ 0.012. Comparison of this value with the component attributable to the actomyosin‐ATPase yields an estimate of 0.15 for the relative contribution of the Ca(2+)‐ATPase to contraction related heat production. 5. The heat production related to the Na+,K(+)‐ATPase in resting preparations was studied by blocking the sodium pump with 400 microM dihydro‐ouabain (DHO). DHO produced a transient decrease in heat rate lasting 1‐2 min, which was followed by a secondary increase. From the heat transient produced by DHO the heat rate related to the Na+,K(+)‐ATPase in the steady state was extrapolated. The relative contribution of the sodium pump to resting heat production was estimated to be 0.17. 6. The heat production related to the Na+,K(+)‐ATPase in contracting preparations was studied by first blocking Ca2+ influx with 100 microM Ca2+ and 400 microM Ni2+, and then inhibiting the sodium pump with 400 microM dihydro‐ouabain (DHO). The relative contribution of the sodium pump to contraction‐related heat production extrapolated from these data was 0.10, which agreed well with the fraction of contraction‐related heat production persisting after blockage of actomyosin‐ATPase and Ca(2+)‐ATPase (0.09).(ABSTRACT TRUNCATED AT 400 WORDS)
Effect of hypoxia on force, intracellular pH and Ca2+ concentration in rat cerebral and mesenteric small arteries.
Authors: Aalkjaer C , Lombard J H
Published: December 2014

1. The effect of severe hypoxia on force, intracellular Ca2+ concentration ([Ca2+]i) and pHi was studied in isolated small arteries from rat brain and rat mesenterium. The arteries were mounted for isometric force recording while [Ca2+]i was measured with fura‐2 or pHi was measured with bis‐carboxyethylcarboxyfluorescein (BCECF). 2. Hypoxia reduced the force development in response to arginine vasopressin (AVP) while [Ca2+]i was unchanged or only slightly reduced. Inhibition of acid extrusion by omission of sodium caused no force development in mesenteric arteries, but the fall in pHi was enhanced during hypoxia. In cerebral arteries, hypoxia reduced the force development associated with omission of sodium, and the fall in pHi was less than during normoxic conditions. When acid extrusion was intact, pHi was not affected by hypoxia and the changes in pHi during activation with AVP were similar during hypoxia and in the control situation. 3. Although a decrease in smooth muscle [Ca2+]i may be partly responsible for the reduced force development during hypoxia, [Ca2+]i‐independent mechanism(s) may play an even more important role. Furthermore, although hypoxia and force development are associated with enhanced acid production, acid extrusion maintains pHi near the control level and it is unlikely that a decrease in smooth muscle pHi plays any role in the reduced force development during hypoxia.
The difference in shape of spontaneous and uniquantal evoked synaptic potentials in frog muscle.
Authors: Cherki-Vakil R , Ginsburg S , Meiri H
Published: December 2014

1. Spontaneous and stimulation‐induced uniquantal synaptic activity at the frog cutaneous pectoris muscle, treated with neostigmine, was recorded by focal extracellular microelectrodes. A monoexponential curve was fitted to the decay of each synaptic response. 2. A highly significant positive relationship was found between the amplitude and the decay time constant of spontaneous extracellular miniature endplate potentials (MEPPs(o)), whereas the relationship displayed by evoked uniquantal extracellular endplate potentials (EPPs(o)) was only slightly greater than zero. 3. The difference did not stem from changes in the muscle membrane conductance or from inclusion of outstanding MEPPs(o) formed as a result of the block of acetylcholinesterase. 4. The dependence of the rise time on the amplitude was also stronger in MEPPs(o) than in EPPs(o). 5. In the absence of neostigmine, MEPPs(o) exhibited a positive correlation between decay time constant and amplitude, while EPPs(o) did not show such a correlation. 6. In view of previously published models of transmitter release, it is suggested that spontaneous secretion of quanta occurs both within and outside the active zones facing postsynaptic areas of variable receptor density.
Responses of human masseter motor units to stretch.
Authors: Miles T S , Poliakov A V , Nordstrom M A
Published: December 2014

1. The reflex responses to stretch were studied in single motor units and the surface electromyogram in human masseter. 2. Controlled stretches of the isometrically contracting jaw‐closing muscles evoked short‐latency (10‐15 ms) and long‐latency (35‐70 ms) excitatory reflex responses in the masseter surface electromyogram. 3. The majority (65%) of tonically active masseter motor units were excited in both short‐ and long‐latency phases of the reflex. The timing of the stimulus determined whether the unit discharged in the short‐ or long‐latency phase. If a non‐tonically active motor unit was recruited by the stimulus, it invariably discharged in the long‐latency phase. 4. Although short‐latency responses were strongly time‐locked to the stimulus, there was very little shortening of interspike intervals (ISIs) in this phase of the reflex. The shortening of ISIs was more prominent and prolonged during the long‐latency phase, which explains why this phase produces most of the reflex force changes following the stretch. 5. Within pairs of concurrently active motor units there was a tenfold range in the size of the short‐latency response to the same stretch. 6. A substantial proportion (35%) of the twenty‐two masseter motor units tested had no statistically significant short‐latency reflex response. 7. In contrast to other human muscles, there was no functional connection between a population of Ia afferents and some masseter motoneurons. There are two possible explanations for this result. The short‐latency, presumably monosynaptic, Ia afferent inputs may not be uniformly distributed to human masseter motoneurons. Alternatively, these inputs may be subject to tonic presynaptic inhibition that is not uniformly distributed throughout the masseter motoneuron pool.
Fatigue and recovery of voluntary and electrically elicited dynamic force in humans.
Authors: Beelen A , Sargeant A J , Jones D A , de Ruiter C J
Published: December 2014

1. Percutaneous electrical stimulation of the human quadriceps muscle has been used to assess the loss of central activation immediately after a bout of fatiguing exercise and during the recovery period. 2. Fatigue was induced in eight healthy males by a maximal effort lasting 25 s performed on an isokinetic cycle ergometer at a constant pedal frequency of 60 revolutions per minute. The cranks of the ergometer were driven by an electric motor. Before and after the sprint, subjects allowed their legs to be passively taken round by the motor. During the passive movement the knee extensors were stimulated (4 pulses; 100 Hz). Peak voluntary force (PVF) during the sprint and peak stimulated forces (PSF) before and in recovery were recorded via strain gauges in the pedals. Recovery of voluntary force was assessed in a series of separate experiments in which subjects performed a second maximal effort after recovery periods of different durations. 3. Peak stimulated forces were reduced to 69.8 +/‐ 9.3% immediately after the maximal effort, (P < 0.05), but had returned to pre‐exercise values after 3 min. The maximum rate of force development (MRFD) was also reduced following fatigue to 68.8 +/‐ 11.0% (P < 0.05) of control and was fully recovered after 2 min. PVF was reduced to 72.0 +/‐ 9.4% (P < 0.05) of the control value following the maximal effort. After 3 min voluntary force had fully recovered. 4. The effect of changing the duration of the fatiguing exercise (10, 25 and 45 s maximal effort) resulted in an increased degree of voluntary force loss as the duration of the maximal effort increased.(ABSTRACT TRUNCATED AT 250 WORDS)
Efficacy of peak Ca2+ currents (ICa) as trigger of sarcoplasmic reticulum Ca2+ release in myocytes from the guinea‐pig coronary artery.
Authors: Ganitkevich VYa  , Isenberg G
Published: December 2014

1. Increments in cytosolic Ca2+ concentration (delta[Ca2+]c) were measured in single smooth muscle cells from guinea‐pig coronary artery together with the density of peak Ca2+ currents (ICa) in response to clamp steps from ‐50 to 0 mV. The comparison of depolarization‐ with caffeine‐induced delta[Ca2+]c was used to define the efficacy by which ICa can trigger Ca2+ release from the sarcoplasmic reticulum (SR). 2. At 2.5 mM extracellular calcium concentration ([Ca2+]o), depolarization induced a rapid rise of delta[Ca2+]c followed by a slow creep. Peak [Ca2+]c occurred within ca 30 s and could be followed by an undershoot and a second rise in [Ca2+]c. The creep was blocked by ryanodine but was insensitive to block of InsP3 receptors with heparin. The creep was not observed in Cs(+)‐filled cells. After disappearance of the creep, a tonic delta[Ca2+]c became unmasked. 3. At 2.5 mM [Ca2+]o, peak ICa was ‐0.80 +/‐ 0.17 microA cm‐2. delta[Ca2+] peaked at the end of the 6 s pulse at 202 +/‐ 98 nM while caffeine‐induced delta[Ca2+]c peaked at 1330 +/‐ 410 nM. The ratio of depolarization‐ to caffeine‐induced delta[Ca2+]c was 10 +/‐ 6%. 4. In media containing 10 mM [Ca2+]o plus 1 microM Bay K 8644, peak ICa was ‐2.6 +/‐ 1.1 microA cm‐2 and delta[Ca2+]c peaked within 2.5 s at 451 +/‐ 194 nM. Paired measurements yielded the ratio of depolarization‐ to caffeine induced delta[Ca2+]c as 30 +/‐ 10%. Depolarization‐induced delta[Ca2+]c was nearly blocked by caffeine and reduced by ryanodine to 30%, suggesting the contribution of Ca2+ release from caffeine‐ and ryanodine‐sensitive Ca2+ stores. 5. Trypsin (1 mg ml‐1) in the electrode solution (10 mM [Ca2+]o plus 1 microM Bay K 8644) increased peak ICa up to 12.5 microA cm‐2. ICa induced a delta[Ca2+]c of 990 +/‐ 210 nM and was accompanied by a ‘hump’ of IK,Ca. When applied briefly after peak delta[Ca2+]c, caffeine increased [Ca2+]c only moderately. The results suggest that a peak ICa can trigger a synchronized whole‐cell Ca2+ release only if ICa is strongly augmented. 6. Amplitude and rate of rise of delta[Ca2+]c were graded by test step potentials along a bell‐shaped voltage‐dependent curve, similar to that of L‐type ICa. Steps to +80 mV induced no delta[Ca2+]c when the electrode solution contained 10 mM Na+. However, with 150 mM intrapipette Na+, pulses to +80 mV induced delta[Ca2+]c.(ABSTRACT TRUNCATED AT 400 WORDS)
Stretch activation of a toad smooth muscle K+ channel may be mediated by fatty acids.
Authors: Ordway R W , Petrou S , Kirber M T , Walsh J V , Singer J J
Published: December 2014

1. using standard single channel patch clamp techniques we studied the stretch sensitivity of a 20 pS K(+)‐selective channel which is activated by fatty acids and found in freshly dissociated smooth muscle cells from the stomach of the toad Bufo marinus. 2. A pulse of suction applied to the back of the patch pipette in order to stretch the membrane resulted in activation of this K+ channel. A train of suction pulses resulted in a gradually increased level of channel activity during each successive pulse, as well as an increase in baseline activity between pulses. This pattern contrasts markedly with many other stretch‐activated channels whose activation is limited to the duration of the suction pulse. 3. Application of fatty acids augmented the response to stretch. In contrast, application of 10 microM defatted albumin, which removes fatty acids from membranes, rapidly and reversibly decreased the response to stretch. 4. These results are consistent with the hypothesis that fatty acids which are generated by mechanical stimuli, perhaps by mechanically activated phospholipases, are the intermediaries in activation of certain mechanically sensitive ion channels.
Multiple components of delayed rectifier K+ current in canine colonic smooth muscle.
Authors: Carl A
Published: December 2014

1. We investigated the pharmacology and voltage‐dependent activation and inactivation kinetics of the ‘delayed rectifier’ K+ current, IdK, in canine colonic myocytes and developed protocols which separate this current into three distinct components that differ in their kinetics and pharmacology. 2. Block of IdK by TEA or 4‐aminopyridine (4‐AP) alone was incomplete. Maximal concentrations of TEA or 4‐AP blocked 76% (EC50 = 2.6 mM) and 51% (EC50 = 69 mM) of current, respectively. In the presence of 10 mM 4‐AP, IdK could be blocked completely by TEA. 3. TEA and 4‐AP had distinct effects on current activation: time constants for activation of IdK at +10 mV were 25.6 +/‐ 4.4 ms under control conditions, 40.3 +/‐ 7.6 ms in the presence of 10 mM 4‐AP and 16.7 +/‐ 2.3 ms with 10 mM TEA in the bath solution. 4‐AP block and removal of block were use dependent, but no frequency dependence or voltage dependence of steady‐state block could be detected. These data are consistent with the presence of a rapidly activating 4‐AP‐sensitive current, IdK(f), and a more slowly activating TEA‐sensitive current component, IdK(s). 4. A third component of the delayed rectifier current, IdK(n), was revealed when 10 mM TEA was included in the pipette solution. IdK(n) was rapidly activating, had a membrane potential at half‐maximal inactivation (V1/2) for steady‐state inactivation 13 mV negative of that for the mixed IdK, was completely insensitive to 4‐AP (10 mM) and was blocked by external TEA with an EC50 of 7.7 mM. 5. These data demonstrate that the delayed rectifier current in canine colonic smooth muscle is composed of three currents, IdK(f), IdK(s) and IdK(n). All three currents are insensitive to charybdotoxin (100 nM).
Zinc potentiation of neurotransmission and inhibition of background cationic conductance in rat cultured hippocampal neurones.
Authors: Nakazawa K , Inoue K , Watano T , Koizumi S , Inoue K
Published: December 2014

1. The facilitation by zinc (Zn2+) of neurotransmission and the mechanisms underlying it were electrophysiologically investigated in rat cultured hippocampal neurones using whole‐cell voltage‐ and current‐clamp techniques. 2. Under whole‐cell voltage clamp with an intracellular solution containing CsCl as a major salt, inward postsynaptic currents were observed at ‐40 mV in a cell culture where a neuronal network had been formed. The postsynaptic currents appeared to be mediated by gamma‐aminobutyric acid (GABA) because the inward currents were abolished when intracellular CsCl was replaced with caesium phosphate and they were blocked by bicuculline (10 microM), an antagonist to GABA‐gated channels. The currents were, however, also blocked by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX, 30 microM), an antagonist to non‐NMDA glutamate‐gated channels, suggesting a contribution of a glutamatergic mechanism to the generation of the currents. Zn2+ (10 and 100 microM) potentiated the postsynaptic currents. 3. In addition to the potentiation of the postsynaptic currents, Zn2+ shifted net membrane current at ‐60 mV in an outward direction. The current‐voltage relationship obtained under various ionic conditions indicated that Zn2+ inhibits a current component which is mainly carried by extracellular Na+. 4. Under whole‐cell current clamp, Zn2+ (10 microM) induced a small hyperpolarization (up to 20 mV), which was accompanied by potentiation of the postsynaptic potentials and spike potentials. Tests were carried out to examine whether changes in resting potential by different protocols mimic responses observed with Zn2+. Hyperpolarization induced by current injection through patch pipettes increased the amplitude of postsynaptic currents, but did not enhance the appearance of spike potentials. In contrast, when extracellular K+ concentration was decreased from 5 to 2.5 mM, cells were hyperpolarized and spike potentials of large amplitude appeared. 5. The results suggest that Zn2+ potentiates neurotransmission and inhibits a background cationic current mainly carried by extracellular Na+ under physiological conditions. The inhibition of the Na+ permeation may increase membrane excitability and thereby contribute to the potentiation of neurotransmission.
Changes in pennation with joint angle and muscle torque: in vivo measurements in human brachialis muscle.
Authors: Herbert R D , Gandevia S C
Published: December 2014

1. Estimates of pennation in human muscles are usually obtained from cadavers. In this study, pennation of human brachialis was measured in vivo using sonography. Effects of static and dynamic changes in elbow angle and torque were investigated. 2. Pennation was measured in eight subjects using an 80 mm, 5 MHz, linear‐array ultrasound transducer to generate sagittal images of the brachialis during maximal and submaximal isometric contractions at various elbow angles. It was shown that estimates of pennation were reproducible, representative of measurements made throughout the belly of the muscle and not distorted by compression of the muscle with the transducer or rotation of the muscle out of the plane of the transducer. 3. Mean resting pennation was 9.0 +/‐ 2.0 deg (S.D., range 6.5‐12.9 deg). When the muscle was relaxed there was no effect of elbow angle on pennation. However, during a maximal isometric contraction (MVC), with the elbow flexed to 90 deg, pennation increased non‐linearly with elbow torque to between 22 and 30 deg (mean 24.7 +/‐ 2.4 deg). The effect of increasing torque was small when the elbow was fully extended. The relationship between elbow angle, elbow torque and brachialis pennation suggests that the relaxed brachialis muscle is slack over much of its physiological range of lengths. 4. There was no hysteresis in the relationship between torque and pennation during slow isometric contractions (0.2 MVC s‐1), and the relationship between elbow angle and pennation was similar during slow shortening and lengthening contractions. 5. Two consequences follow from these findings. Firstly, intramuscular mechanics are complex and simple planar models of muscles underestimate the increases in pennation which occur during muscle contraction. Second, spindle afferents from relaxed muscles may not encode joint angle over the full range of movement.
Characteristic features of inhibitory junction potentials evoked by single stimuli in the guinea‐pig isolated taenia caeci.
Authors: Bridgewater M , Cunnane T C , Brading A F
Published: December 2014

1. Changes in membrane potential of the guinea‐pig isolated taenia caeci evoked by single stimuli have been investigated using intracellular recording techniques. Nifedipine (10 microM) was used to arrest spontaneous muscle action potentials. Single stimuli elicited complex junction potentials which consisted of both excitatory and inhibitory components. 2. The excitatory component of the compound junction potential was unaffected by hexamethonium (100 microM) but abolished by atropine (1 microM) and omega‐conotoxin GVIA (10‐100 nM). 3. In the presence of atropine, single stimuli elicited fast inhibitory junction potentials (IJPs). IJPs were sometimes biphasic during repolarization with a noticeable ‘slow tail’. Apamin (30‐100 nM) potently inhibited the fast IJP and revealed an underlying slow IJP. 4. The fast IJP was also abolished by omega‐conotoxin GVIA (100 nM). However, the slow IJP was insensitive to omega‐conotoxin GVIA but was abolished by cadmium (30 microM). 5. Guanethidine (3 microM) and N omega‐nitro‐L‐arginine (10‐100 microM) had no detectable effects on either of the IJPs. The dye Reactive Blue 2 reduced the amplitude of the fast IJP but this reduction was associated with a membrane hyperpolarization. 6. The existence of two distinct IJPs in the guinea‐pig taenia caeci has been demonstrated. The ability of omega‐conotoxin GVIA to selectively abolish the fast IJP leaving the slow IJP intact suggests that separate nerves are involved in mediating these responses.
Warm and cold signals from the preoptic area: which contribute more to the control of shivering in rats?
Authors: Zhang Y H , Yanase-Fujiwara M , Hosono T , Kanosue K
Published: December 2014

1. To find out whether the thermosensitive neurones in the preoptic area that control shivering are predominantly warm or cold sensitive, we tested the effects of injecting the excitatory amino acid L‐glutamate at various sites in and adjacent to the preoptic area of anaesthetized rats shivering at ambient temperatures of 15‐21 degrees C. 2. L‐Glutamate injections (0.2 mM in 0.5‐1.0 microliter), as well as preoptic warming and electrical stimulation, suppressed shivering, whereas control saline injections had no effect. Effective sites were restricted to the anterior part of the preoptic area, and a tenfold lower concentration of L‐glutamate did not influence shivering. 3. Injections of procaine (0.2 M) into the sites where L‐glutamate suppressed shivering did not affect strong shivering activity, but facilitated shivering in three out of seven cases when shivering was weak or absent at higher ambient temperatures (25‐30 degrees C). 4. L‐Glutamate injections, as well as preoptic warming and electrical stimulation, also elicited vasodilatation of the paw skin and the tail. Procaine elicited vasoconstriction when it was applied during vasodilatation induced by local preoptic warming. 5. These results indicate that the contribution of the preoptic area to the control of shivering and vasomotion is influenced more by signals from warm‐sensitive neurones than by signals from cold‐sensitive neurones.
Tachykinins as mediators of slow EPSPs in guinea‐pig gall‐bladder ganglia: involvement of neurokinin‐3 receptors.
Authors: Mawe G M
Published: December 2014

1. The effects of endogenous tachykinins and related peptides on intact guinea‐pig gall‐bladder neurones were investigated with single‐electrode voltage‐ and current‐clamp recording techniques. 2. Pressure ejection of substance P (100 microM) caused a long lasting membrane depolarization that was associated with a decrease in input resistance. In cells that were voltage‐clamped to their resting membrane potential, substance P activated an inward current. 3. The reversal potentials of the substance P‐induced depolarization and inward current were congruent to 0 mV. In a low‐Na+ solution, the substance P‐induced depolarization and inward current were reduced in amplitude. 4. Substance P increased the excitability of neurones, as evidenced by a greater anodal break activity and an increase in the number of action potentials generated during a depolarizing current pulse. 5. Substance P, neurokinin A (NKA) and neurokinin B (NKB) were applied by superfusion to determine the relative potencies of these tachykinins. NKB was the most potent, with an EC50 of 24 nM. The EC50 values for NKA and substance P were 47.8 and 281 nM, respectively. 6. The neurokinin‐3 (NK‐3) receptor agonist senktide depolarized neurones with an EC50 of 6.3 nM. Neither the NK‐1 receptor agonist [Sar9,Met(O2)11]‐substance P nor the NK‐2 receptor agonist [beta‐Ala8]‐NKA(4‐10) caused a measurable depolarization. 7. The NK‐3 antagonist [Trp7,beta‐Ala8]‐NKA (4‐10) inhibited the responsiveness of gall‐bladder neurones to substance P with a KB (dissociation constant of receptor antagonist) of 49 nM, and depressed both capsaicin‐induced depolarizations and stimulus‐evoked slow EPSPs. 8. These data indicate that tachykinins mediate slow EPSPs in guinea‐pig gall‐bladder ganglia by activating NK‐3 receptors on gall‐bladder neurones. It is proposed that in response to inflammation or high intraluminal pressure, tachykinins may be released within ganglia by sensory fibres and act directly on intrinsic neurones to facilitate ganglionic transmission.