bluuebunny/crossref_metadata_2025_split huggingface dataset:
Opposing effects of phorbol esters on transmitter release and calcium currents at frog motor nerve endings
Authors: Redman R.S. , Searl T.J. , Hirsh J.K. , Silinsky E.M. 
Published: September 2004

Phorbol esters activate protein kinase C (PKC) and also increase the secretion of neuro‐transmitter substances by an unknown mechanism. To evaluate whether the stimulatory effects of such agents on acetylcholine (ACh) secretion occur as a consequence of stimulation of Ca2+ entry, we made electrophysiological measurements of ACh secretion (i.e. endplate potentials, EPPs) and the component of the prejunctional perineural voltage change associated with nerve terminal calcium currents (perineural calcium current) at frog neuro‐muscular junctions.
In the first series of experiments, modest concentrations of K+ channel blockers were employed so that simultaneous measurements of EPP amplitudes and perineural calcium currents could be made. In these experiments, 12‐O‐tetradecanoylphorbol 13‐acetate (TPA; 162 nm) and phorbol 12,13‐dibutyrate (PDBu; 100‐200 nm) each increased ACh release but simultaneously decreased the calcium component of the prejunctional perineural current. TPA and PDBu also inhibited perineural calcium currents in the presence of higher concentrations of K+ channel blockers.
Blockade of Ca2+ channels by Cd2+ prevented the action of PKC stimulators on perineural waveforms.
The inactive compound 4‐α‐phorbol 12‐myristate 13‐acetate (150 nm) did not affect EPP amplitudes or perineural currents.
The extracellular [Ca2+]‐ACh release relationship was increased in maximum by PDBu without any change in the potency of Ca2+ to support evoked ACh release.
The results demonstrate that phorbol esters increase neurotransmitter secretion whilst simultaneously decreasing the nerve ending calcium currents that promote evoked release. The results, which suggest that the optimal control point for secretion might not be the calcium channel but rather a component of the secretory apparatus, are discussed in conjunction with the possible target sites for phorbol esters in the nerve ending.
Selective Enhancement of the Slow Component of Delayed Rectifier K+ Current in Guinea‐Pig Atrial Cells by External ATP
Authors: Matsimra Hiroshi , Ehara Tsuguhisa 
Published: September 2004

The effects of external ATP on the rapidly and slowly activating components (IKr and IKg, respectively) of the delayed rectifier K+ current (IK) in guinea‐pig atrial myocytes were determined using the whole‐cell configuration of the patch‐clamp technique.
An envelope of tails test was conducted by applying depolarizing pulses to +40 mV from a holding potential of −40 mV for various durations between 50 ms and 2 s under control conditions and during exposure to 50 μM ATP. The ATP‐induced IK, obtained by digital subtraction, exhibited a constant ratio (0.37) of the tail current to time‐dependent current, regardless of the pulse duration. This current ratio was compatible with the predicted ratio of the driving force at +40 and −40 mV for a non‐rectifying K+ conductance, suggesting that the ATP‐induced IK is due primarily to IKs.
The amplitude of IKr isolated from the IK enhanced by ATP, determined as an E‐4031 (5 μM)‐sensitive current, was similar to the control magnitude of IKr, thus showing that external ATP did not cause an increase in IKr.
The voltage‐dependent activation of the ATP‐induced IK during 500 ms depolarizing test pulses could be described by a Boltzmann equation with a half‐activation voltage (V1/2) of 11.5 mV and slope factor (k) of 12.0 mV, which were close to those of IKg(V1/4 of 12.1 mV and k of 12.3 mV), determined as an E‐4031‐resistant IK, under the same isochronal (500 ms) activation conditions.
These results provide evidence to suggest that extracellular ATP selectively potentiates the slow component of IK (IKg), with no measurable effects on IKr, in guinea‐pig atrial myocytes.
Photodynamic triggering of calcium oscillation in the isolated rat pancreatic acini
Authors: Cui Zong Jie , Kanno Tomio 
Published: September 2004

Photodynamic agents, due to their photon‐dependent selective activation, can selectively activate a number of physiological processes and may directly modulate signal transduction in a number of cells including pancreatic acinar cells.
Activation of the photodynamic agent sulphonated aluminium phthalocyanine (SALPC) triggered recurrent cytosolic calcium ([Ca2+]i) spiking in pancreatic acinar cells.
The photodynamically triggered calcium spiking could be blocked by phosphatidylinositol‐specific phospholipase C (PI‐PLC) inhibitor U73122, but not by phosphatidylcholine‐specific phospholipase C inhibitor D609.
Removal of extracellular Ca2+ abolished spiking, as did 2‐aminoethoxydiphenylborate (2‐APB), an inhibitory modulator of IP3‐mediated Ca2+ release from intracellular stores.
These data suggest that SALPC photodynamic action may permanently fix PI‐PLC in an active conformation, and this produced recurrent [Ca2+]i spiking.
Developmental changes in isolated rat type I carotid body cell K+ currents and their modulation by hypoxia
Authors: Hatton C. J. , Carpenter E. , Pepper D. R. , Kumar P. , Peers C. 
Published: September 2004

Whole‐cell patch‐clamp recordings were used to investigate possible age‐related changes in K+ currents of type I carotid body cells isolated from the rat. K+ current density increased with age, as measured in cells isolated from 4‐day‐old, 10‐day‐old and adult rats (≥ 5 weeks old).
The proportion of current reversibly inhibited by high [Mg2+] (6 mm), low [Ca2+] (0.1 mm) solutions, indicative of the proportion of current attributable to activation of Ca2+‐sensitive K+ (KCa) channels, was significantly smaller in cells of 4‐day‐old rats compared with 10‐dayold rats, despite inward Ca2+ current densities being similar in these two age groups. Inhibition of K+ currents by high [Mg2+], low [Ca2+] solutions was similar in 10‐day‐old and adult type I cells.
Hypoxia (PO2, 16–23 mmHg) caused reversible reductions in type I cells from rats of all age groups. However, reductions seen in cells of 4‐day‐old rats were significantly smaller than those seen in cells of 10‐day‐olds and adults. The degree of hypoxic inhibition in these latter two groups was not significantly different.
In the presence of high [Mg2+], low [Ca2+] solutions, hypoxia (PO2, 16–23 mmHg) was without significant effect on residual K+ currents in cells from all age groups.
These observations indicate that K+ current density increases with postnatal age in the rat. Between days 4 and 10, there appears to be a predominant enhancement of KCa channels, and over the same age range hypoxic sensitivity of K+ currents increases. Our findings demonstrate that this latter observation arises because hypoxia selectively inhibits KCa channels in cells at all ages studied. These results suggest an important role for KCa channels in postnatal maturation of hypoxic chemoreception in the rat carotid body.
Modulation of Ca2+‐activated Cl− currents in rabbit portal vein smooth muscle by an inhibitor of mitochondrial Ca2+ uptake
Authors: Greenwood I. A. , Helliwell R. M. , Large W. A. 
Published: September 2004

The effects of carbonyl cyanide m‐chlorophenyl hydrazone (CCCP), an inhibitor of mitochondrial Ca2+ uptake, was investigated on the properties of Ca2+‐activated chloride currents (ICl(Ca)) in rabbit portal vein smooth muscle cells using the perforated patch whole‐cell voltage‐clamp technique to ascertain whether this Ca2+ uptake process influences the time course of the subsarcolemmal Ca2+ signal that activates ICl(Ca).
In cells bathed in either physiological calcium (2 mm Ca2+o) or high calcium (10 mm Ca2+o) external solutions, application of CCCP (1–2 μm) evoked an inward current and prolonged the exponential decay time constant (τ) of Ca2+‐activated Cl−‘tail’ currents (Itall) evoked by Ca2+ influx through voltage‐dependent calcium channels (VDCCs). The effect of CCCP on τ was greater in cells where the amplitude of Itall was relatively large and, in different cells, the effect of CCCP on T was positively correlated with the amplitude of Itall.
CCCP abolished spontaneously occurring transient Ca2+‐activated Cl− currents (STICs), but did not alter their time course before complete block.
Thapsigargin and cyclopiazonic acid (inhibitors of the sarcoplasmic Ca2+‐ATPase) inhibited STICs, but did not affect the decay of Itall or STICs.
In conclusion, when Ca2+ enters the cell through VDCCs, the time course of the consequent Ca2+ signal in the subsarcolemmal domain containing Ca2+‐activated chloride channels appears to be regulated by Ca2+ uptake into mitochondria. In contrast, inhibition of Ca2+ uptake by the sarcoplasmic reticulum ATPase does not seem to influence the time course of ICl(Ca).
Volume‐activated DIDS‐sensitive whole‐cell chloride currents in trout red blood cells
Authors: Egée Stéphane , Harvey† Brian J. , Thomas Serge 
Published: September 2004

The nystatin‐perforated whole‐cell recording mode of the patch‐clamp technique was used to investigate the membrane conductance of trout (Oncorhynchus mykiss) red blood cells in the steady state, 5 min after exposure to hyposmotic medium and 10 min after return to normal isosmotic medium.
Whole‐cell I–V relations showed outward rectification when red blood cells were bathed in isosmotic (320 mosmol l−1) saline solution and the patch pipette was filled with 117 mm KCl. The membrane conductance was 2.58 ± 0.59 nS (number of experiments, n=18) between 0 and 100 mV and 1.32 ± 0.19 nS (n=18) between 0 and −100 mV. Removal of Cl− from the extracellular side or incubation with the CL−1 channel blocker DIDS caused a reduction in whole‐cell membrane conductance by more than 50%, indicating that the membrane current was generated by Cl− ions. The remaining conductance was voltage independent and probably due to non‐selective cation conductance.
The membrane conductance increased approximately 2‐fold after cell swelling induced by exposure to hyposmotic saline solution (215 mosmol I1). This effect was abolished in Cl−1‐free hyposmotic medium or in the presence of DIDS.
The return to isosmotic solution produced a fall in membrane conductance to, or below, control values.
We conclude that trout red blood cells possess a significant Cl− conductance in the steady state which is reversibly activated during cell swelling and contributes to volume recovery.
Tachykinin‐induced activation of non‐specific cation conductance via nk3 neurokinin receptors in guinea‐pig intracardiac neurones
Authors: Hardwick Jean C. , Mawe Gary M. , Parsons Rodney L. 
Published: September 2004

Whole mount preparations from guinea‐pig hearts were used to characterize the receptors and ionic mechanisms mediating the substance P (SP)‐induced depolarization of para‐sympathetic postganglionic neurones of the cardiac ganglion.
Measurement of the amplitude of depolarization in response to superfusion of different tachykinin agonists (neurokinins A (NKA) and B (NKB), SP, and senktide) gave a rank‐order potency of NKB=senktide > NKA > SP, indicating involvement of an NK3 receptor. The use of the selective tachykinin receptor antagonists SR 140333, SR 48986, and SR 142801 demonstrated that only the NK3 receptor antagonist SR 142801 inhibited the SP‐induced depolarization.
The SP‐induced depolarization was not inhibited by Ba2+, TEA, or niflumic acid, or altered by reduced Cl− solutions, but was attenuated in reduced Na+ solutions. Single electrode voltage clamp studies demonstrated that the SP‐induced inward current increased in amplitude at more negative potentials, had a reversal potential of approximately 0 mV, and was reduced in amplitude in reduced Na+ solutions.
We conclude that the SP‐induced depolarization in guinea‐pig postganglionic parasympathetic neurones of the cardiac ganglion is due to NK3‐mediated activation of a non‐selective cation conductance.
Fractional Ca2+ Currents through Capsaicin‐ and Proton‐Activated Ion Channels in Rat Dorsal Root Ganglion Neurones
Authors: Zeilhofer Hanns Ulrich , Kress Michaela , Swandulla Dieter 
Published: September 2004

Capsaicin and protons cause excitation and sensitization of primary nociceptive afferents. In a subset of dorsal root ganglion (DRG) neurones, which probably represent nociceptive neurones, both capsaicin and protons induce slowly inactivating non‐selective cation currents. Whole‐cell as well as single channel currents activated by these two stimuli share many biophysical and physiological properties in these neurones. This has lead to the suggestion that protons and capsaicin might activate the same ion channels.
In this study we simultaneously measured fluorescence signals and whole‐cell currents activated by capsaicin or protons in acutely isolated DRG neurones filled with a high concentration (1 mM) of the Ca2+ indicator dye fura‐2. From these measurements the fractional contribution of Ca2+ (Pf; the portion of the whole‐cell current carried by Ca2+) to capsaicin‐ and two types of proton‐induced (fast and slowly inactivating) membrane currents was determined.
Capsaicin‐ and slowly inactivating proton‐induced currents were accompanied by a change in fluorescence that was dependent on the presence of extracellular Ca2+. With 1.6 mM extracellular Ca2+ and at a holding potential of −80 mV Pf of capsaicin‐induced currents (at pH 7.3) was 4.30 ± 0.17% (mean ±s.e.m.; no. of experiments, n= 16) and of slowly inactivating proton‐induced currents (at pH 5.1) was 1.65 ± 0.11% (n= 17). Pf of fast inactivating proton‐induced currents was negligible.
P
f of capsaicin‐ and slowly inactivating proton‐induced currents increased with increasing extracellular Ca2+ concentration (0.5–4.8 mM).
P
f of both current types decreased linearly with decreasing extracellular pH by about 0.7% per pH unit over the pH range investigated. When determined at the same extracellular pH Pf values were significantly different for the two current types at all pH values tested.
In summary, our results provide evidence that capsaicin and protons activate ion channels which are markedly permeable to Ca2+. The fractional contribution of Ca2+, however, was significantly different for capsaicin‐ and slowly inactivating proton‐induced currents. This strongly suggests that the two stimuli activate different populations of ion channels and supports the possibility that Ca2+ influx through these channels may be important for Ca2+‐dependent sensitization of primary nociceptive neurones.
Modulation by adenosine of GABA‐activated current in rat dorsal root ganglion neurons
Authors: Hu Hong‐Zhen , Li Zhi‐Wang 
Published: September 2004

The modulation by adenosine of GABA‐activated current (IGABA) was studied in freshly isolated rat dorsal root ganglion (DRG) neurons using the whole‐cell patch‐clamp technique.
In most of the DRG neurons examined (68/90, 75.5%) adenosine (1–100 μm) suppressed Igaba, while in some neurons examined, it potentiated (16/90, 17.8%) Igaba. It exerted no effects on Igaba in a few cells (6/90, 6.7%).
Adenosine shifted the GABA concentration–response curve downward with no significant change of the EC50. The maximal response to GABA was suppressed by 29.6 ± 2.6%. The adenosine‐induced inhibition of Igaba showed no voltage dependence.
8‐Cyclopentyl‐1,3‐dimethylxanthine (DPCPX; 1 μm), a selective A1 adenosine receptor antagonist, partially reversed adenosine inhibition of Igaba and completely blocked N6‐cyclo‐hexyladenosine (CHA; an A1 adenosine receptor agonist) inhibition of IGABA. DPCPX (1 μm) also blocked the suppression of Igaba by 2‐chloroadenosine (CADO). CGS 21680, a selective A2A adenosine receptor agonist, did not inhibit Igaba and DMPX, a selective A2A adenosine receptor antagonist, did not prevent adenosine inhibition of Igaba.
Intracellular application of H‐7 (20 μm; a protein kinase C inhibitor) reversed adenosine inhibition of Igaba while inclusion of cAMP (1 mm), H‐9 (20 μm; a protein kinase A inhibitor) and BAPTA (10 mm; a chelator of calcium ions) in the recording pipette did not affect the depression of Igaba by adenosine. Igaba was also suppressed by internal perfusion of PMA, a protein kinase C activator.
The results suggest that adenosine, as a neuromodulator, exerts a modulatory effect on the GABA‐induced presynaptic inhibition in primary sensory transmission.
Chloride conductance in mouse muscle is subject to post‐transcriptional compensation of the functional Cl− channel 1 gene dosage
Authors: Chen Mei‐fang , Niggeweg Ricarda , Iaizzo Paul A. , Lehmann‐Horn Frank , Jockusch Harald 
Published: September 2004

In mature mammalian muscle, the muscular chloride channel ClC‐1 contributes about 75% of the sarcolemmal resting conductance (Gm). In mice carrying two defective alleles of the corresponding Clc1 gene, chloride conductance (GCl) is reduced to less than 10% of that of wild‐type, and this causes hyperexcitability, the salient feature of the disease myotonia. Potassium conductance (GK) values in myotonic mouse muscle fibres are lowered by about 60% compared with wild‐type.
The defective Clcadr allele causes loss of the 4.5 kb ClC‐1 mRNA. Mice heterozygous for the defective Clc1adr allele contain about 50% functional mRNA in their muscles compared with homozygous wild‐type mice.
Despite a halved functional gene dosage, heterozygous muscles display an average GCl which is not significantly different from that of homozygous wild‐type animals. The GK values in heterozygotes are also indistinguishable from homozygous wild‐type animals.
These results indicate that a regulatory mechanism acting at the post‐transcriptional level limits the density of ClC‐1 channels. GK is probably indirectly regulated by muscle activity.
ATP‐dependent desensitization of the muscarinic K+ channel in rat atrial cells
Authors: Shui Z. , Boyett M. R. , Zang W.‐J. 
Published: September 2004

Fast desensitization of the muscarinic K+ channel has been studied in excised patches from rat atrial cells.
In inside‐out patches, ACh was present in the pipette and GTP was applied via the bath to activate the channel. In outside‐out patches, GTP was present in the pipette and ACh was applied via the bath to activate the channel. In both cases, during a 30 s exposure to GTP or ACh there was a decline in channel activity as a result of fast desensitization if ATP was present.
In inside‐out patches, fast desensitization was still observed if the muscarinic ACh receptor was bypassed and the channel was activated by GTPγS. This suggests that fast desensitization is a result of a modification of the channel (or the connecting G protein) and not the receptor.
In both inside‐out and outside‐out patches, channel activity was depressed and fast desensitization was reduced or absent, if ATP was not present.
The non‐hydrolysable analogue of ATP, AMP‐PNP, did not substitute for ATP in its effects on the channel.
The results are consistent with the hypothesis that fast desensitization of the muscarinic K+ channel is the result of a dephosphorylation of the channel.
Lack of Regulation by Intracellular Ca2+ of the Hyper Polarization‐Activated Cation Current in Rat Thalamic Neurones
Authors: Budde Thomas , Biella Gerardo , Munsch Thomas , Pape Hans‐Christian 
Published: September 2004

The regulation of the hyperpolarization‐activated cation current, Ih, in thalamocortical neurones by intracellular calcium ions has been implemented in a number of mathematical models on the waxing and waning behaviour of synchronized rhythmic activity in thalamocortical circuits. In the present study, the Ca2+ dependence of Ih in thalamocortical neurones was experimentally investigated by combining Ca2+ imaging and patch‐clamp techniques in the ventrobasal thalamic complex (VB) in vitro.
Properties of Ih were analysed before and during rhythmic stimulation of Ca2+ entry by trains of depolarizing voltage pulses. Despite a significant increase in intracellular Ca2+ concentration ([Ca2+]i) from resting levels of 74 ± 23 nM to 251 ± 78 nM upon rhythmic stimulation, significant differences in the voltage dependence of Ih activation did not occur (half‐maximal activation at −86.4 ± l.3 mV vs.−85.2 ± 2.9 mV; slope of the activation curve, 11.2 ± 2.4 mV vs. 12.5 ± 2.5 mV). Recording of Ih with predefined values of [Ca2+]i (13.2 nM or 10.01 μm in the patch pipette) revealed no significant differences in the activation curve or the fully activated I–V relationship of Ih.
In comparison, stimulation of the intracellular cyclic adenosine monophosphate (cAMP) pathway induced a significantly positive shift in Ih voltage dependence of +5.1 ± l.9 mV, with no alteration in the fully activated I–V relationship.
These data argue against a direct regulation of Ih by intracellular Ca2+, and particularly do not support a primary role of Ca2+‐dependent modulation of the Ih channels in the waxing and waning of sleep spindle oscillations in thalamocortical neurones.
Stimulation‐induced changes in [ca2+] in lizard motor nerve terminals
Authors: David Gavriel , Barrett John N. , Barrett Ellen F. 
Published: September 2004

Motor axons were injected ionophoretically with one of five Ca2+‐sensitive dyes (fluo‐3, Calcium Green‐2, Calcium Green‐5N, fluo‐3FF and Oregon Green BAPTA‐5N). Changes in fluorescence (ΔF/Frest) within motor terminal boutons following a single action potential and brief stimulus trains were monitored with high temporal resolution using a confocal microscope.
Stimulation‐induced increases in ΔF/Frest were confined primarily to boutons, with roughly uniform increases in all the boutons of a terminal. The increase in ΔF/Frest began prior to, and decayed more slowly than, the endplate potential (EPP) recorded in the underlying muscle fibre. ΔF/Frest was graded with bath [Ca2+]. Both ΔF/Frest and the EPP were reduced, but not eliminated, by ω‐conotoxin GVIA (5–10 μm).
For dyes with lower affinity for Ca2+ (e.g. Oregon Green BAPTA‐5N, Kd≈ mm) stimulation‐induced increases in ΔF/Frest were measured in the presence of the K+ channel blocker 3,4‐diaminopyridine (3,4‐DAP, 100 mm). During brief stimulus trains (4 at 50 Hz) in 3,4‐DAP, the EPP exhibited profound depression, but the fluorescence increase associated with each stimulus showed little decrement, suggesting that depression was not mediated by a reduction in Ca2+ entry.
For dyes with a higher affinity for Ca2+ (e.g. fluo‐3, Kd≈ 0.5–1 μm) stimulation‐induced increases in ΔF/Frest could also be measured in normal physiological saline. Increases in ΔF/Frest were much greater with 3,4‐DAP present, but the amplitude decreased with successive stimuli due to partial dye saturation.
Calculations suggested that following a single action potential the average [Ca2+] within a bouton increased by up to 150 nm in normal saline and 940 nM in 3,4‐DAP. With low affinity dyes the ΔF/Frest measured near the membrane had a higher peak amplitude and a faster early decay than that measured in the centre of the bouton, suggesting that substantial spatial [Ca2+] gradients exist within boutons for at least 15 ms following stimulation.