Effects of acidosis and NO on nicorandil-activated K(ATP) channels in guinea-pig ventricular myocytes.
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ABSTRACT:
SUBMITTER: Moncada GA
PROVIDER: S-EPMC1572434 | biostudies-other | 2000 Nov
REPOSITORIES: biostudies-other
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Project description:The effects of the antiarrhythmic drug flecainide on levcromakalim-induced hyperpolarization, macroscopic and unitary K(+) currents in pig urethra were investigated using patch-clamp techniques. The effects of flecainide were also examined on currents in inside-out patches of COS7 cells expressing carboxy terminus truncated inwardly rectifying K(+) channel (Kir6.2) subunits (i.e. Kir6.2DeltaC36) which form ATP-sensitive K(+) channels (K(ATP) channels). In current-clamp mode, application of flecainide (> or =100 microM) caused a significant depolarization after the membrane potential had been hyperpolarized by levcromakalim. In voltage-clamp experiments, the levcromakalim-induced outward current was suppressed by 300 microM flecainide in quasi-physiological K(+) conditions (K(i)=51 microM). In contrast, approximately 20% of the levcromakalim-induced inward current still remained even after application of 300 microM flecainide in symmetrical 140 mM K(+) conditions (K(i)=51 microM). In contrast, approximately 20% of the levcromakalim-induced inwar=126 microM). In cell-attached configuration, the channel activity of the levcromakalim-induced K(ATP) channels was reversibly inhibited by flecainide (> or =30 microM) at -50 mV. Their activity was also suppressed by either disopyramide or cibenzoline. Flecainide reversibly inhibited the channel activity of Kir6.2DeltaC36 expressed in COS7 cells using inside-out configuration. Inhibitory effects of flecainide on the levcromakalim-induced currents became more potent when the value of external pH increased, although this slightly reduced the proportion of drug molecules carrying a positive charge. These results suggest that flecainide inhibits channel activity through blocking the pore site of the K(ATP) channel in pig urethra.
| S-EPMC1572826 | biostudies-other
Project description:1. The modulation of large conductance Ca(2+)-activated K(+) (BK(Ca)) channels by the nitric oxide (NO(.)) donor, S-nitroso-L-cysteine (NOCys) and three sulfhydryl-specific methanethiosulfonate (MTS) reagents, positively charged 2-aminoethyl MTS hydrobromide (MTSEA C(3)H(9)NO(2)S(2)HBr) and [2-(trimethylammonium) ethyl MTS bromide (MTSET C(6)H(16)NO(2)S(2)Br), and negatively charged sodium (2-sulfonatoethyl) MTS (MTSES C(3)H(7)O(5)S(3)Na) were compared in excised inside-out membrane patches of the guinea-pig taenia caeca. 2. In membrane patches bathed in a low Ca(2+) (15 nM) high K(+) physiological salt solution, 1-3 BK(Ca) channels opened with a low probability (N.P(o)) of 0.019+/-0.011 at 0 mV. N.P(o) readily increased with membrane depolarization, raised Ca(2+) concentration or upon the addition of NOCys (10 micro M for 2-5 min) such that 5-15 open BK(Ca) channels were evident. 3. MTSEA (2.5 mM) decreased, while MTSES (2.5 mM) increased N.P(o) (at 0 mV) and the number of open BK(Ca) channels at positive potentials. These changes in channel activity remained after a prolonged washout of these two MTS reagents. 4. MTSET (2.5 mM) increased N.P(o) (at 0 mV) and voltage-dependently decreased BK(Ca) current amplitudes in a manner readily reversed upon washout. 5. Pre-exposure of excised membrane patches to MTSES or N-ethylmaleimide (NEM 1 mM), a specific alkylating agent of cysteine sulfhydryls, but not MTSEA or MTSET, prevented the excitatory actions of NOCys (10 micro M). 6. It was concluded that NOCys-evoked increases in BK(Ca) channel activity occur via the S-nitrosylation of cysteine residues within basic regions of the channel alpha subunit that have an accessible water interface.
| S-EPMC1573943 | biostudies-literature
Project description:Calcium sparks are the elementary Ca2+ release events in excitation-contraction coupling that underlie the Ca2+ transient. The frequency-dependent contractile force generated by cardiac myocytes depends upon the characteristics of the Ca2+ transients. A stochastic computational local control model of a guinea pig ventricular cardiomyocyte was developed, to gain insight into mechanisms of force-frequency relationship (FFR). This required the creation of a new three-state RyR2 model that reproduced the adaptive behavior of RyR2, in which the RyR2 channels transition into a different state when exposed to prolonged elevated subspace [Ca2+]. The model simulations agree with previous experimental and modeling studies on interval-force relations. Unlike previous common pool models, this local control model displayed stable action potential trains at 7 Hz. The duration and the amplitude of the [Ca2+]myo transients increase in pacing rates consistent with the experiments. The [Ca2+]myo transient reaches its peak value at 4 Hz and decreases afterward, consistent with experimental force-frequency curves. The model predicts, in agreement with previous modeling studies of Jafri and co-workers, diastolic sarcoplasmic reticulum, [Ca2+]sr, and RyR2 adaptation increase with the increased stimulation frequency, producing rising, rather than falling, amplitude of the myoplasmic [Ca2+] transients. However, the local control model also suggests that the reduction of the L-type Ca2+ current, with an increase in pacing frequency due to Ca2+-dependent inactivation, also plays a role in the negative slope of the FFR. In the simulations, the peak Ca2+ transient in the FFR correlated with the highest numbers of SR Ca2+ sparks: the larger average amplitudes of those sparks, and the longer duration of the Ca2+ sparks.
| S-EPMC9687237 | biostudies-literature
Project description:AimsCalmodulin (CaM) regulates Na+ channel gating through binding to an IQ-like motif in the C-terminus. Ca2+/CaM-dependent protein kinase II (CaMKII) regulates Ca2+ handling, and chronic overactivity of CaMKII is associated with left ventricular hypertrophy and dysfunction and lethal arrhythmias. However, the acute effects of Ca2+/CaM and CaMKII on cardiac Na+ channels are not fully understood.Methods and resultsPurified Na(V)1.5-glutathione-S-transferase fusion peptides were phosphorylated in vitro by CaMKII predominantly on the I-II linker. Whole-cell voltage-clamp was used to measure Na+ current (I(Na)) in isolated guinea-pig ventricular myocytes in the absence or presence of CaM or CaMKII in the pipette solution. CaMKII shifted the voltage dependence of Na+ channel availability by approximately +5 mV, hastened recovery from inactivation, decreased entry into intermediate or slow inactivation, and increased persistent (late) current, but did not change I(Na) decay. These CaMKII-induced changes of Na+ channel gating were completely abolished by a specific CaMKII inhibitor, autocamtide-2-related inhibitory peptide (AIP). Ca2+/CaM alone reproduced the CaMKII-induced changes of I(Na) availability and the fraction of channels undergoing slow inactivation, but did not alter recovery from inactivation or the magnitude of the late current. Furthermore, the CaM-induced changes were also completely abolished by AIP. On the other hand, cAMP-dependent protein kinase A inhibitors did not abolish the CaM/CaMKII-induced alterations of I(Na) function.ConclusionCa2+/CaM and CaMKII have distinct effects on the inactivation phenotype of cardiac Na+ channels. The differences are consistent with CaM-independent effects of CaMKII on cardiac Na+ channel gating.
| S-EPMC2802203 | biostudies-literature
Project description:BACKGROUND AND PURPOSE: Stonefish (Synanceia genus) are commonly found in shallow waters of the Pacific and Indian Oceans. The venom of stonefish is stored in the dorsal fine spines and contains a proteinaceous toxin, verrucotoxin (VTX). The stings produced by the spines induce intense pain, respiratory weakness, damage to the cardiovascular system, convulsions and paralysis, sometimes leading to death. Although there are many studies on VTX, the mechanism(s) underlying the VTX-mediated cardiotoxicity is not yet fully understood. The aim of this study was to investigate the modulation of ion channels in cardiac tissue by VTX. EXPERIMENTAL APPROACH: The effects of VTX on changes in the voltage or current in guinea-pig ventricular myocytes were investigated using a patch clamp method. KEY RESULTS: VTX (10 microg ml(-1)) prolonged the action potential duration by 2.5-fold. VTX increased L-type Ca(2+) currents (I (Ca(L))) in a concentration-dependent manner with a EC(50) value of 7 microg ml(-1) and a maximum increase of 3.1-fold. The non-selective beta-adrenoceptor antagonist, propranolol (1 microM) and the selective beta(1)-adrenoceptor antagonist, CGP20712A (10 microM) each abolished the effect of VTX (100 microg ml(-1)) on I (Ca(L)). Furthermore, the protein kinase A (PKA) antagonists H-89 (10 microM) and Rp-8-Br-cAMPS (30 microM) inhibited the effect of VTX on I (Ca(L)). CONCLUSIONS AND IMPLICATIONS: VTX modulates Ca(2+) channel activity through the beta-adrenoceptor-cAMP-PKA pathway.
| S-EPMC2189832 | biostudies-other
Project description:AimsSpontaneous Ca2+ waves in cardiomyocytes are potentially arrhythmogenic. A powerful controller of Ca2+ waves is the cytoplasmic H+ concentration ([H+]i), which fluctuates spatially and temporally in conditions such as myocardial ischaemia/reperfusion. H+-control of Ca2+ waves is poorly understood. We have therefore investigated how [H+]i co-ordinates their initiation and frequency.Methods and resultsSpontaneous Ca2+ waves were imaged (fluo-3) in rat isolated ventricular myocytes, subjected to modest Ca2+-overload. Whole-cell intracellular acidosis (induced by acetate-superfusion) stimulated wave frequency. Pharmacologically blocking sarcolemmal Na+/H+ exchange (NHE1) prevented this stimulation, unveiling inhibition by H+. Acidosis also increased Ca2+ wave velocity. Restricting acidosis to one end of a myocyte, using a microfluidic device, inhibited Ca2+ waves in the acidic zone (consistent with ryanodine receptor inhibition), but stimulated wave emergence elsewhere in the cell. This remote stimulation was absent when NHE1 was selectively inhibited in the acidic zone. Remote stimulation depended on a locally evoked, NHE1-driven rise of [Na+]i that spread rapidly downstream.ConclusionAcidosis influences Ca2+ waves via inhibitory Hi+ and stimulatory Nai+ signals (the latter facilitating intracellular Ca2+-loading through modulation of sarcolemmal Na+/Ca2+ exchange activity). During spatial [H+]i-heterogeneity, Hi+-inhibition dominates in acidic regions, while rapid Nai+ diffusion stimulates waves in downstream, non-acidic regions. Local acidosis thus simultaneously inhibits and stimulates arrhythmogenic Ca2+-signalling in the same myocyte. If the principle of remote H+-stimulation of Ca2+ waves also applies in multicellular myocardium, it raises the possibility of electrical disturbances being driven remotely by adjacent ischaemic areas, which are known to be intensely acidic.
| S-EPMC5852542 | biostudies-literature
Project description:1. Using the whole-cell voltage clamp technique, the effect of aprindine on Na+/Ca2+ exchange current (I(NCX)) was examined in guinea-pig single cardiac ventricular myocytes and CCL39 fibroblasts expressing a dog cardiac Na+/Ca2+ exchanger (NCX1). 2. I(NCX) was recorded by ramp pulses from the holding potential of -60 mV with the external solution containing 140 mM Na+ and 1 mM Ca2+, and the pipette solution containing 20 mM Na+, 20 mM BAPTA and 13 mM Ca2+ (433 nM free Ca2+). 3. External application of aprindine suppressed I(NCX) in a concentration-dependent manner. The IC50 values of outward (measured at 50 mV) and inward (measured at -100 mV) I(NCX) components were 48.8 and 51.8 microM with Hill coefficients of 1.3 and 1, respectively. 4. Intracellular application of trypsin via the pipette solution did not change the blocking effect of aprindine, suggesting that aprindine does not affect the exchanger from the cytoplasmic side. 5. Aprindine inhibited I(NCX) of a mutant NCX1 with a deletion of amino acids 247 - 671 in the large intracellular domain between the transmembrane segments 5 and 6 in a similar manner to that of the wild-type, suggesting that the site of aprindine inhibition is not in the large intracellular domain of NCX1. 6. A kinetic study indicated that aprindine was cooperatively competitive with KB-R7943, another inhibitor of NCX and that aprindine was a competitive inhibitor with respect to external Ca2+. 7. We conclude that aprindine may modestly inhibit I(NCX) in a therapeutic range of concentrations (around 2.5 approximately 6.9 microM) possibly at an external or intra-membranous site of the exchanger.
| S-EPMC1573359 | biostudies-other
Project description:AIM: The present study investigated the effect of adenosine on Na(+)-K(+) pumps in acutely isolated guinea pig (Cavia sp.) ventricular myocytes. METHODS: The whole-cell, patch-clamp technique was used to record the Na(+)-K(+) pump current (I(p)) in acutely isolated guinea pig ventricular myocytes. RESULTS: Adenosine inhibited the high DHO-affinity pump current (I(h)) in a concentration-dependent manner, which was blocked by the selective adenosine A(1) receptor antagonist DPCPX and the general protein kinase C (PKC) antagonists staurosporine, GF 109203X or the specific delta isoform antagonist rottlerin. In addition, the inhibitory action of adenosine was mimicked by a selective A(1) receptor agonist CCPA and a specific activator peptide of PKC-delta, PP114. In contrast, the selective A(2A) receptor agonist CGS21680 and A(3) receptor agonist Cl-IB-MECA did not affect I(h). Application of the selective A(2A) receptor antagonist SCH58261 and A(3) receptor antagonist MRS1191 also failed to block the effect of adenosine. Furthermore, H89, a selective protein kinase A (PKA) antagonist, did not exert any effect on adenosine-induced I(h) inhibition. CONCLUSION: The present study provides the electrophysiological evidence that adenosine can induce significant inhibition of I(h) via adenosine A(1) receptors and the PKC-delta isoform.
| S-EPMC4002279 | biostudies-other
Project description:Chlorthalidone is used for the treatment of hypertension as it produces a lengthening of the cardiac action potential. However, there is no experimental evidence that chlorthalidone has electrophysiological effects on the potassium currents involved in cardiac repolarization.Ventricular myocytes and oocytes, transfected with human ionic channels that produce IK current, were exposed to different concentrations of chlorthalidone. Action potentials and potassium currents were recorded using a patch clamp technique. To determine which component of the current was affected by chlorthalidone, human channel proteins (hERG, minK and KvLQT1) were used.Chlorthalidone prolonged the ventricular action potential at 50 and 90% by 13 and 14%, respectively. The cardiac potassium currents I(to) and IK(1) were not affected by chlorthalidone at any concentration, whereas the delayed rectifier potassium current, IK, was blocked in a dose-response, voltage-independent fashion. In our preparation, 100 microM chlorthalidone blocked the two components of the delayed rectifier potassium current with the same potency (50.1+/-5% for IK(r) and 54.6+/-6% for IK(s)) (n=7, P<0.05). The chlorthalidone-sensitive current was slow and saturated at potentials greater than +30 mV. In our conditions only the KvLQT1 potassium current was affected by the drug, by 14%.Chlorthalidone was demonstrated to have a direct effect on cardiac ventricular myocytes; it blocked the delayed rectifier potassium current (IK), specifically the KvLQT1 component of the potassium current. These results indicate that it has potential for use as an antiarrhythmic but further studies are needed.
| S-EPMC2241797 | biostudies-other
Project description:BACKGROUND AND PURPOSE The Ca(2+) paradox is an important phenomenon associated with Ca(2+) overload-mediated cellular injury in myocardium. The present study was undertaken to elucidate molecular and cellular mechanisms for the development of the Ca(2+) paradox. EXPERIMENTAL APPROACH Fluorescence imaging was performed on fluo-3 loaded quiescent mouse ventricular myocytes using confocal laser scanning microscope. KEY RESULTS The Ca(2+) paradox was readily evoked by restoration of the extracellular Ca(2+) following 10-20?min of nominally Ca(2+)-free superfusion. The Ca(2+) paradox was significantly reduced by blockers of transient receptor potential canonical (TRPC) channels (2-aminoethoxydiphenyl borate, Gd(3+), La(3+)) and anti-TRPC1 antibody. The sarcoplasmic reticulum (SR) Ca(2+) content, assessed by caffeine application, gradually declined during Ca(2+)-free superfusion, which was further accelerated by metabolic inhibition. Block of SR Ca(2+) leak by tetracaine prevented Ca(2+) paradox. The Na(+) /Ca(2+) exchange (NCX) blocker KB-R7943 significantly inhibited Ca(2+) paradox when applied throughout superfusion period, but had little effect when added for a period of 3?min before and during Ca(2+) restoration. The SR Ca(2+) content was better preserved during Ca(2+) depletion by KB-R7943. Immunocytochemistry confirmed the expression of TRPC1, in addition to TRPC3 and TRPC4, in mouse ventricular myocytes. CONCLUSIONS AND IMPLICATIONS These results provide evidence that (i) the Ca(2+) paradox is primarily mediated by Ca(2+) entry through TRPC (probably TRPC1) channels that are presumably activated by SR Ca(2+) depletion; and (ii) reverse mode NCX contributes little to the Ca(2+) paradox, whereas inhibition of NCX during Ca(2+) depletion improves SR Ca(2+) loading, and is associated with reduced incidence of Ca(2+) paradox in mouse ventricular myocytes.
| S-EPMC3010579 | biostudies-literature