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At least 667 records · Page 37Linked to original sources
PubMed2001

Activation of barium-sensitive inward rectifier potassium channels mediates remote dilation of coronary arterioles.

BACKGROUND: Conducted vasodilation seems to be critical for the functional distribution of blood flow in the skeletal muscle microcirculation. However, this vasoregulatory phenomenon has not been documented in the coronary microcirculation, and its underlying mechanism remains elusive. Because potassium ions are potent metabolic vasodilators in the heart, by activating vascular inward rectifier K(+) (K(ir)) channels, we tested the hypothesis that coronary arterioles exhibit remote vasodilation through activation of this type of channel. METHODS AND RESULTS: Porcine coronary arterioles were isolated, cannulated, and pressurized for in vitro study. Vessels dilated concentration-dependently to extraluminal KCl (5 to 20 mmol/L), bradykinin, adenosine, pinacidil, and sodium nitroprusside. A K(ir) channel blocker, BaCl(2) (30 micromol/L), inhibited vasodilatory responses to KCl and bradykinin but not to adenosine, pinacidil, or nitroprusside. In a flow chamber, localized administration of bradykinin, adenosine, and KCl to the downstream end of the arterioles caused approximately 80% dilation at the site of drug application (local site) and also produced 30% to 60% dilation at the upstream end of arterioles (remote site). Nitroprusside produced a similar dilation at the local site but failed to initiate remote vasodilation. In the presence of Ba(2+), adenosine still dilated the local site, but the local dilations to bradykinin and KCl and the remote dilations to adenosine, bradykinin, and KCl were inhibited. CONCLUSIONS: We demonstrated that some modes of local vasodilation can be conducted to remote sites in coronary arterioles and that local and remote dilations can occur through different vasodilatory mechanisms. Activation of K(ir) channels seems critical for some agonist-induced local vasodilations and also for the initiation and/or transmission of signals causing remote vasodilation.

Adenosine↗
PubMed1997

Frequency-dependent Cardiac Electrophysiologic Effects of Tedisamil: Comparison With Quinidine and Sotalol.

BACKGROUND: Tedisamil is a potent bradycardiac/antiischemic drug known to lengthen cadiac repolarization by blocking various potassium channels. Recent in vivo experiments revealed that it is an antiarrhythmic agent. It was therefore of interest to compare the cellular electrophysiologic effects of tedisamil with those of quinidine and sotalol in isolated cardiac preparations. METHODS AND RESULTS: The conventional microelectrode technique was applied in isolated dog cardiac Purkinje and ventricular muscle fibers and in rabbit left atrial muscle. Tedisamil (1 µM) and sotalol (30 µM) lengthened, while quinidine (10 µM) shortened action potential duration in dog Purkinje fibers. The phase 1 repolarization was delayed by tedisamil and quinidine and not changed by sotalol. In dog ventricular muscle and in rabbit atrial muscle, all three drugs studied lengthened repolarization. In dog Purkinje fiber, tedisamil and sotalol lengthened action potential duration more at slow than at high stimulation frequency (reverse use-dependence). In dog ventricular muscle fibers, the effect of the drugs was not clearly frequency dependent. In rabbit atrial muscle fibers, the quinidine-evoked repolarization lengthening was most pronounced at intermediate cycle lengths (500-1000 ms). Tedisamil and quinidine but not sotalol depressed the maximal rate of depolarization (V(max)), which depended on the stimulation frequency (use-dependence). The nature of the use-dependent V(max) block differed between quinidine and tedisamil. Quinidine decreased V(max) at a relatively wide range of stimulation frequencies whle tedisamil. Quinidine decreased V(max) at a relatively wide range of stimulation frequencies while tedisamil decreased V(max) largely at high rate of stimulation. Tedisamil and quiinidine prevented or decreased the pinacidil-evoked action potential shortening in dog ventricular muscle, suggesting block of the ATP-dependent potassium channels (I(KATP)), while with sotalol such effect was not observed. CONCLUSIONS: Although tedisamil, quinidine, and sotalol are known to lengthen the QT interval, their cellular electrophysiologic effects substantially differ. Tedisamil lengthens repolarization and prevents pinacidil-evoked action potential duration shortening, suggesting I(K(ATP)) blockade. Its effect on the V(max) is limited mostly to fast heart rate. These electrophysiologic effects of tedisamil resemble those of chronic amiodarone treatment.

Journal Article↗
PubMed1996

Calcitonin gene-related peptide rapidly inhibits calcium uptake in osteoblastic cell lines via activation of adenosine triphosphate-sensitive potassium channels.

In certain neurons, alternative RNA processing generates calcitonin gene-related peptide (CGRP) from the same gene that encodes the hormone calcitonin. As CGRP-containing nerve fibers are prominent in skeleton, we evaluated the effects of CGRP on osteoblasts. Because the vasodilatory effect of neural CGRP in smooth muscle probably involves inhibition of unstimulated Ca2+ uptake, we examined the acute effects of CGRP on this parameter in rat osteoblastic cells. CGRP inhibits 45Ca2+ uptake in both UMR 106 osteosarcoma and RCOB-3 osteoblastic cells. This inhibition is rapid (0.5 min), occurs with an EC50 of 1 nM, and cannot be demonstrated in the presence of 0.1 mM diltiazem, a blocker of voltage-dependent Ca2+ channels. Depolarization of bone cells with high extracellular potassium (K+) also blocks the effect of CGRP on 45Ca2+ uptake, suggesting a central role for K+ channels in mediating this action. In agreement with this hypothesis, the effect of CGRP is blocked by 1 microM glybenclamide, a specific inhibitor of ATP-sensitive potassium (K(ATP)) channels, or by pretreatment of cells with 1 mM iodoacetic acid to deplete intracellular ATP. Blocking Ca2+-activated potassium channels with 1 mM tetraethylammonium does not prevent CGRP's effect. Pinacidil, a specific activator of K(ATP) channels, mimics CGRP's effect. Both CGRP and pinacidil also produce a small significant stimulation of cellular Ca2+ efflux in UMR 106 cells. These data suggest that inhibition of diltiazem-sensitive Ca2+ channels occurs secondary to the hyperpolarization engendered by CGRP activation of K(ATP) channels in osteoblastic cells, an effect similar to that of CGRP on smooth muscle cells.

Adenosine Triphosphate↗
PubMed1999

Comparative studies on the relaxing action of several adenosine 5'-triphosphate-sensitive K+ channel openers in pig urethra.

The relaxing effects of the adenosine 5'-triphosphate (ATP)-sensitive K+ channel openers (K(ATP) openers; diazoxide, minoxidil, pinacidil, (+/-)-cromakalim, (+)-cromakalim and (-)-cromakalim) were investigated on the resting tone of pig proximal urethra. In addition, patch clamp techniques were utilized for recording cromakalim-induced ionic currents in cells dispersed from the same urethral region. The (-)-cromakalim-induced relaxation of urethral muscle strips was stable, reversible and reproducible. The rank order of potency regarding of K(ATP) openers in lowering the resting urethral tone was (-)-cromakalim>pinacidil>diazoxide>minoxidil. K(ATP) opener-induced urethral relaxation was suppressed by subsequent application of glibenclamide (1 microM). (+)-Cromakalim (< or =10 microM) did not relax the urethra nor antagonize the (-)-cromakalim-induced urethral relaxation. However, at higher concentrations, (+)-cromakalim (> or =30 microM) caused a small but significant urethral relaxation. In accordance with these observations, the relaxation induced by 5 microM (-)-cromakalim was identical to that induced by 10 microM (+/-)-cromakalim, as expected from a theoretical half potency for (+/-)-cromakalim. In whole-cell recording, (-)-cromakalim and (+) cromakalim (100 microM) activated a glibenclamide-sensitive outward current which was due to the activation of the glibenclamide-sensitive 43 pS K+ channel (K(GS)-43 pS). The potency of (+)-cromakalim to activate K(GS)-43 pS was much weaker than that of (-)-cromakalim. These results indicate that the ability of K(ATP) openers to relax pig urethral smooth muscle can be accounted for by activation of glibenclamide-sensitive K+ channels.

Adenosine Triphosphate↗
PubMed2004

Protective effect of N-acetylcysteine against oxygen radical-mediated coronary artery injury.

The present study investigated the protective effect of N-acetylcysteine (NAC) against oxygen radical-mediated coronary artery injury. Vascular contraction and relaxation were determined in canine coronary arteries immersed in Kreb's solution (95% O2-5% CO2), incubated or not with NAC (10 mM), and exposed to free radicals (FR) generated by xanthine oxidase (100 mU/ml) plus xanthine (0.1 mM). Rings not exposed to FR or NAC were used as controls. The arteries were contracted with 2.5 microM prostaglandin F2alpha. Subsequently, concentration-response curves for acetylcholine, calcium ionophore and sodium fluoride were obtained in the presence of 20 microM indomethacin. Concentration-response curves for bradykinin, calcium ionophore, sodium nitroprusside, and pinacidil were obtained in the presence of indomethacin plus Nomega-nitro-L-arginine (0.2 mM). The oxidative stress reduced the vascular contraction of arteries not exposed to NAC (3.93 +/- 3.42 g), compared to control (8.56 +/- 3.16 g) and to NAC group (9.07 +/- 4.0 g). Additionally, in arteries not exposed to NAC the endothelium-dependent nitric oxide (NO)-dependent relaxation promoted by acetylcholine (1 nM to 10 microM) was also reduced (maximal relaxation of 52.1 +/- 43.2%), compared to control (100%) and NAC group (97.0 +/- 4.3%), as well as the NO/cyclooxygenase-independent receptor-dependent relaxation provoked by bradykinin (1 nM to 10 microM; maximal relaxation of 20.0 +/- 21.2%), compared to control (100%) and NAC group (70.8 +/- 20.0%). The endothelium-independent relaxation elicited by sodium nitroprusside (1 nM to 1 microM) and pinacidil (1 nM to 10 microM) was not affected. In conclusion, the vascular dysfunction caused by the oxidative stress, expressed as reduction of the endothelium-dependent relaxation and of the vascular smooth muscle contraction, was prevented by NAC.

Acetylcysteine↗
PubMed2001

Protein kinase C and G(i/o) proteins are involved in adenosine- and ischemic preconditioning-mediated renal protection.

Renal ischemic reperfusion (IR) injury is a significant clinical problem in anesthesia and surgery. Recently, it was demonstrated that both renal ischemic preconditioning (IPC) and systemic adenosine pretreatment protect against renal IR injury. In cardiac IPC, pertussis toxin-sensitive G-proteins (i.e., G(i/o)), protein kinase C (PKC), and ATP-sensitive potassium (K+(ATP)) channels are implicated in this protective signaling pathway. The aim of this study was to elucidate the signaling pathways that are responsible for renal protection mediated by both IPC and adenosine pretreatment. In addition, because A1 adenosine receptor antagonist failed to block renal IPC, whether activation of bradykinin, muscarinic, or opioid receptors can mimic renal IPC was tested because these receptors have been implicated in cardiac IPC. Rats were acutely pretreated with chelerythrine or glibenclamide, selective blockers of PKC and K+(ATP) channels, respectively, before IPC or adenosine pretreatment. Some rats were pretreated with pinacidil (K+(ATP)channel opener), bradykinin, methacholine, or morphine before renal ischemia. Twenty-four h later, plasma creatinine was measured. Separate groups of rats received pertussis toxin intraperitoneally 48 h before being subjected to the above protective protocols. IPC and adenosine pretreatment protected against renal IR injury. Pretreatment with pertussis toxin and chelerythrine abolished the protective effects of both renal IPC and adenosine. However, glibenclamide pretreatment had no effect on either renal IPC or adenosine-induced renal protection, indicating no apparent role for K+(ATP) channels. Moreover, pinacidil, bradykinin, methacholine, and morphine failed to protect renal function. Therefore, the conclusion is that cellular signal transduction pathways of renal IPC and adenosine pretreatment in vivo involve G(i/o) proteins and PKC but not K+(ATP) channels. Unlike cardiac IPC, bradykinin, muscarinic, and opioid receptors do not mediate renal IPC.

Adenosine↗
PubMed1999

Pharmacological and histochemical distinctions between molecularly defined sarcolemmal KATP channels and native cardiac mitochondrial KATP channels.

A variety of direct and indirect techniques have revealed the existence of ATP-sensitive potassium (KATP) channels in the inner membranes of mitochondria. The molecular identity of these mitochondrial KATP (mitoKATP) channels remains unclear. We used a pharmacological approach to distinguish mitoKATP channels from classical, molecularly defined cardiac sarcolemmal KATP (surfaceKATP) channels encoded by the sulfonylurea receptor SUR2A and the pore-forming subunit Kir6.2. SUR2A and Kir6.2 were expressed in human embryonic kidney (HEK)293 cells, and their activities were measured by patch-clamp recordings of membrane current. SurfaceKATP channels are activated potently by 100 microM pinacidil but only weakly by 100 microM diazoxide; in addition, they are blocked by 10 microM glibenclamide, but are insensitive to 500 microM 5-hydroxydecanoate. This pharmacology, which was confirmed with patch-clamp recordings in intact rabbit ventricular myocytes, contrasts with that of mitoKATP channels as indexed by flavoprotein oxidation. MitoKATP channels in myocytes are activated equally by 100 microM diazoxide and 100 microM pinacidil. In contrast to its lack of effect on surfaceKATP channels, 5-hydroxydecanoate is an effective blocker of mitoKATP channels. Glibenclamide's effects on mitoKATP channels are difficult to assess, because it independently activates flavoprotein fluorescence, consistent with a previously described primary uncoupling effect. Confocal imaging of the subcellular distribution of expressed fluorescent Kir6.2 in HEK cells and in myocytes revealed no targeting of mitochondrial membranes. The differences in drug sensitivity and subcellular localization indicate that mitoKATP channels are distinct from surface KATP channels at a molecular level.

Animals↗
PubMed2000

Inhibition of alpha(1)-adrenergic-mediated responses in rat ventricular myocytes by adenosine A(1) receptor activation: role of the K(ATP) channel.

Both beta- and alpha(1)-adrenoceptors mediate the myocardial effects of catecholamines. It is well known that adenosine inhibits beta-dependent effects; however, whether alpha(1)-dependent responses can be similarly modulated is unclear. Accordingly, rat ventricular myocytes were exposed for 25 min to the alpha(1) agonist phenylephrine (2 microM, in the presence of 1 microM propranolol) in the absence or presence of adenosine (100 microM) or the A(1) receptor-selective agonist N(6)-cyclopentyladenosine (CPA, 1 microM). We also investigated the effects of K(ATP) blockade with glibenclamide (1 microM), the protein kinase C inhibitor bisindolylmaleimide (20 nM), and pertussis toxin (300 ng/ml), which uncouples G(i) protein/receptor interaction, and assessed whether effects of adenosine were mimicked by K(ATP) activation with either pinacidil or cromakalim (5 microM). Phenylephrine significantly increased cell shortening by 190% and the Ca(2+) transient by 24%, which was abolished by either adenosine or CPA, but not in the presence of the A(1) receptor-selective antagonist 8-cyclopentyl-1, 3-dipropylxanthine (1 microM), and was abolished by pertussis toxin. The effect of adenosine or CPA was reversed by glibenclamide and mimicked by either cromakalim or pinacidil. Bisindolylmaleimide was without effect. The A(2) or A(3) receptor agonists 2-(4-(2-carboxyethyl)phenylethylamino)-5'-N-ethylcarboxamidoade nos ine and N(6)-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (1 microM each), respectively, were without effect. Neither CPA nor adenosine modulated the effect of endothelin-1 (5 nM), which also acts via the phosphoinositide hydrolysis pathway. We conclude that adenosine selectively inhibits alpha(1)-adrenergic-mediated effects in rat ventricular myocytes through a G(i) protein-dependent mechanism involving A(1) receptor and K(ATP) activation. Our study further suggests that endogenous adenosine may modulate alpha(1)-mediated effects of catecholamines.

Adenosine↗
PubMed1992

A specific binding site for K+ channel openers in rat aorta.

The K+ channel openers, including cromakalim, pinacidil, minoxidil sulfate, diazoxide, and nicorandil, form a chemically heterogeneous group of compounds, which relax smooth muscle by opening plasmalemmal K+ channels. At present it is not known whether these drugs elicit their effects by binding to the same target, presumably the K+ channel. In order to address this question, a binding assay for K+ channel openers has been developed in vascular smooth muscle. The novel tritiated K+ channel opener, [3H]P1075, an analogue of pinacidil, binds with high affinity (KD = 6 +/- 1 nM) to endothelium-denuded rings of rat aorta. Inhibition studies indicate that the different families of K+ channel openers bind to a common target. Evidence is presented to suggest that the binding site for the sulfonylurea, glibenclamide, the major blocker of the K+ channel openers, is coupled in a negative allosteric manner to the binding site(s) for the openers. The binding assay described here may open the way to the biochemical characterization of the drug receptor for the K+ channel openers.

Animals↗
PubMed1993

4-morpholinecarboximidine-N-1-adamantyl-N'-cyclohexylhydrochloride (U-37883A): pharmacological characterization of a novel antagonist of vascular ATP-sensitive K+ channel openers.

This study describes the in vitro and in vivo characteristics of a guanidine 4-morpholinecarboximidine-N-1-adamantyl-N'-cyclohexyl-hydroc hloride (U-37883A), as an antagonist of vascular ATP-sensitive K+ channels (KATP). In isolated rabbit mesenteric artery, the antagonistic effects of U-37883A (0.5-5 microM) were studied against vasorelaxation produced by cromakalim (0.5 microM), minoxidil sulfate (5 microM), pinacidil (1 microM) and RP-49356 (1 microM). The dose-response curves for U-37883A against all four potassium channel openers were similar with U-37883A, IC50S ranging from 0.78 to 1.4 microM, suggesting that U-37883A is producing inhibition by acting at a step that is common to all four potassium channel openers during their activation of the vascular KATP. In contrast, U-37883A at 10 microM did not inhibit relaxation dose-response curves by nitroglycerine, forskolin or D600. U-37883A (1 or 10 microM) effectively inhibited as well as reversed 42K efflux-stimulated by cromakalim (1 microM) or minoxidil sulfate (5 microM). Finally, U-37883A (3 mg/kg i.v.) was found to inhibit significantly as well as reverse hypotension produced by minoxidil (1 mg/kg i.v. or 3 mg/kg p.o.), cromakalim (0.5 mg/kg p.o.) and pinacidil (0.3 mg/kg i.v.) in rats, cats and dogs. In contrast, the in vivo responses to phenylephrine, nitroglycerine, sodium nitroprusside or isoproterenol were not altered. U-37883A thus appears to be the first nonsulfonylurea shown to block consistently and selectively the in vitro as well as the in vivo pharmacological responses to various potassium channel openers. This structurally novel KATP antagonist therefore would be useful for further characterizing the mechanisms of pharmacological modulation of the KATP in a variety of cell systems.

Adamantane↗
PubMed2002

The effects of drugs modulating K(+) transport on Rb(+) uptake and distribution in pig hearts following regional ischemia: (87)Rb MRI study.

The effects of drugs that can modulate passive permeability of K(+) into cardiomyocytes in normal and reperfusion-damaged cardiac muscle were assessed. Rubidium ion (Rb(+)) was used as a K(+) tracer and (87)Rb-MRI as a detection method. The left anterior descending artery (LAD) of isolated pig hearts perfused with Krebs-Henseleit buffer (KHB) was occluded for 2 h and subsequently reperfused for 2 h with KHB containing 4.7 mM RbCl instead of KCl. The buffer contained either a blocker of ATP-sensitive K(+) channels (K(ATP)), glibenclamide (Glib, 3 micro M), a K(ATP) opener, pinacidil (Pin, 10 micro M), a K(+)/Na(+)/2Cl(-) co-transporter inhibitor, bumetanide (Bum, 10 micro M) or no drug (control). Upon reperfusion three-dimensional (87)Rb MR images were acquired to obtain kinetics of Rb(+) uptake and its distribution. Areas at risk (AAR) and areas of necrosis were determined by Evans Blue and triphenyl tetrazolium chloride staining, respectively. Rb(+) uptake kinetics in the remote posterior (Pos) wall were similar in all groups. The kinetics remained monoexponential in the affected anterior (Ant) wall and the uptake rates were 32, 36, 37 and 21% of that in the Pos wall in the control, Glib, Pin and Bum groups, respectively. Infarct sizes determined histologically as a percentage of total ventricular (left + right) mass (14-22%) corresponded to sizes of areas with 20-40% of maximal Rb image intensity [I(Rb)(max), 15-22%], except for the Pin group (12.5 vs 21%). The sizes of areas with 20-50% of I(Rb)(max) (30-36%) closely correlated with those of AAR determined histologically (31-33%). Lactate dehydrogenase release did not differ in all groups. We conclude that: (1) reperfusion damage quickly inhibits Rb(+) uptake; (2) Rb(+) uptake in normal and reperfused tissue does not significantly depend on K(ATP) or the K(+)/Na(+)/2Cl(-) cotransporter; (3) areas with 20-40% of maximal image intensity correspond to infarct areas.

Animals↗
PubMed1993

High affinity binding of a potassium channel agonist to intact rat insulinoma cells.

The specific binding of a novel tritiated K+ channel opener, [3H]BAY X 9228, has been characterized in a rat insulinoma (RINm5F) cell line. The KD was 2.1 nM and Bmax 50 fmol/mg total protein as determined by saturation analysis. The high affinity binding to intact cells was inhibited by pinacidil and by a series of BAY X 9228 analogs with an activity sequence correlating well with that for producing glyburide-reversible relaxation of partially depolarized rat aorta. This represents the first report of the specific binding of a K+ channel opener to cultured cells.

Animals↗
PubMed1993

Comparison of in vitro effects of cicletanine, its enantiomers and major metabolite on rat thoracic aorta.

The effects of cicletanine ((+/-)-cic)), its optical isomers (BN-50417,(+)-cic); (BN-50418,(-)-cic) and major metabolite (BN-50699,cic-Met) on active tension were investigated in rat thoracic aortas. (+/-)-cic, (+)-cic, (-)-cic shifted the K(+)-concentration response curve to the right and depressed the maximum contractile response. Cic-Met was devoid of inhibitory effect on K(+)-induced contractions. (-)-Pinacidil had a far more potent inhibitory effect on K(+)-induced contractions than the cicletanine enantiomers and shifted the K(+)-concentration response curve to the right without affecting the maximum contractile response. (+/-)-Cic and nifedipine caused a concentration-related inhibition of Ca(2+)-induced contractions. Nifedipine was far more potent than (+/-)-cic in this respect. The slope of the Schild plot for nifedipine was not different from unity contrary to the significantly different slope for (+/-)-cic. (+/-)-Cic, (+)-cic, (-)-cic and cic-Met (3 x 10(-5) M to 3 x 10(-4) M) caused a concentration-related relaxation of noradrenaline (NA), serotonin (5-HT) and prostaglandin F2 alpha (PGF2 alpha)-induced contractions. In NA-precontracted preparations (-)-cic (10(-4) M-3 x 10(-4) M) had a stronger relaxant effect than (+)-cic. Cic-Met was a weaker antagonist of NA-induced contractions than (+) and (-)-cic. The enantiomers were far less potent relaxing NA-induced contractions than phentolamine. (+)-Cic, (-)-cic and cic-Met had a similar relaxant effect on 5-HT-induced contractions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

ATP-sensitive K+ channel opener acts as a potent Cl- channel inhibitor in vascular smooth muscle cells.

We describe the activation of a K+ current and inhibition of a Cl- current by a cyanoguanidine activator of ATP-sensitive K+ channels (KATP) in the smooth muscle cell line A10. The efficacy of U83757, an analogue of pinacidil, as an activator of KATP was confirmed in single channel experiments on isolated ventricular myocytes. The effects of U83757 were examined in the clonal smooth muscle cell line A10 using voltage-sensitive dyes and digital fluorescent imaging techniques. Exposure of A10 cells to U83757 (10 nM to 1 microM) produced a rapid membrane hyperpolarization as monitored by the membrane potential-sensitive dye bis-oxonol ([diBAC4(3)], 5 microM). The U83757-induced hyperpolarization was antagonized by glyburide and tetrapropylammonium (TPrA) but not by tetraethlyl-ammonium (TEA) or charybdotoxin (ChTX). The molecular basis of the observed hyperpolarization was studied in whole-cell, voltage-clamp experiments. Exposure of voltage-clamped cells to U83757 (300 nM to 300 microM) produced a hyperpolarizing shift in the zero current potential; however, the hyperpolarizing shift in reversal potential was associated with either an increase or decrease in membrane conductance. In solutions where EK = -82 mV and ECl = 0 mV, the reversal potential of the U83757-sensitive current was approximately -70 mV in those experiments where an increase in membrane conductance was observed. In experiments in which a decrease in conductance was observed, the reversal potential of the U83757-sensitive current was approximately 0 mV, suggesting that U83757 might be acting as a Cl- channel blocker as well as a K+ channel opener. In experiments in which Cl- current activation was specifically brought about by cellular swelling and performed in solutions where Cl- was the major permeant ion, U83757 (300 nM to 300 microM) produced a dose-dependent current inhibition. Taken together these results (i) demonstrate the presence of a K(+)-selective current which is sensitive to KATP channel openers in A10 cells and (ii) indicate that the hyperpolarizing effects of K+ channel openers in vascular smooth muscle may be due to both the inhibition of Cl- currents as well as the activation of a K(+)-selective current.

Adenosine Triphosphate↗
PubMed1995

Modifications by chronic intermittent hypoxia and drug treatment on skeletal muscle metabolism.

The energy metabolism was evaluated in gastrocnemius muscle from 3-month-old rats subjected to either mild or severe 4-week intermittent normobaric hypoxia. Furthermore, 4-week treatment with CNS-acting drugs, namely, alpha-adrenergic (delta-yohimbine), vasodilator (papaverine, pinacidil), or oxygen-increasing (almitrine) agents was performed. The muscular concentration of the following metabolites was evaluated: glycogen, glucose, glucose 6-phosphate, pyruvate, lactate, lactate-to-pyruvate ratio; citrate, alpha-ketoglutarate, succinate, malate; aspartate, glutamate, alanine; ammonia; ATP, ADP, AMP, creatine phosphate. Furthermore the Vmax of the following muscular enzymes was evaluated: hexokinase, phosphofructokinase, pyruvate kinase, lactate dehydrogenase; citrate synthase, malate dehydrogenase; total NADH cytochrome c reductase; cytochrome oxidase. The adaptation to chronic intermittent normobaric mild or severe hypoxia induced alterations of the components in the anaerobic glycolytic pathway [as supported by the increased activity of lactate dehydrogenase and/or hexokinase, resulting in the decreased glycolytic substrate concentration consistent with the increased lactate production and lactate-to-pyruvate ratio] and in the mitochondrial mechanism [as supported by the decreased activity of malate dehydrogenase and/or citrate synthase resulting in the decreased concentration of some key components in the tricarboxylic acid cycle]. The effect of the concomitant pharmacological treatment suggests that the action of CNS-acting drugs could be also related to their direct influence on the muscular biochemical mechanisms linked to energy transduction.

Adenine Nucleotides↗
PubMed1991

Analysis and use of the perforated patch technique for recording ionic currents in pancreatic beta-cells.

We have used the nystatin perforated patch technique to study ionic currents in rat pancreatic beta-cells. The access resistance (Ra) between the pipette and the cell cytoplasm, measured by analyzing capacitive currents, decreased with a slow exponential time course (tau = 5.4 +/- 2.7 min) after seal formation. As Ra decreased, the magnitude of voltage-dependent K and Ca currents increased with a similar time course, and their activation kinetics became faster. After Ra stabilized, the macroscopic currents remained stable for up to an hour or more. When the final Ra was sufficiently low, Ca tail currents could be resolved which had properties similar to those recorded with the classical whole-cell technique. Two types of K channels could be characterized with perforated patch recordings of macroscopic K currents: (i) ATP-blockable K (KATP) channels which generate a time and voltage independent current that is blocked by glyburide and enhanced by pinacidil and (ii) voltage-dependent K (Kv) channels. Whole-cell recordings of KATP currents in the absence of ATP in the pipette showed that the maximum KATP conductance of the beta-cell was 83.8 +/- 40 nS. Perforated patch recordings show that the resting KATP conductance is 3.57 +/- 2.09 nS, which corresponds to about 4% of the channels being open in the intact beta-cell. In classical whole-cell recordings. Kv activation kinetics become faster during the first 10-15 min of recording, probably due to a dissipating Donnan potential. In perforated patch recordings where the Donnan potential is very small, Kv activation kinetics were nearly identical to the steady-state whole cell measurements.

Adenosine Triphosphate↗
PubMed2002

Opening of ATP-sensitive potassium channels causes generation of free radicals in vascular smooth muscle cells.

Recent evidence suggests that opening of mitochondrial K(ATP) channels in cardiac muscle triggers the preconditioning phenomenon through free radical production. The present study tested the effects of K(ATP) channel openers in a vascular smooth muscle cell model using the fluorescent probe MitoTracker (MTR) Red trade mark for detection of reactive oxygen species (ROS). Rat aortic smooth muscle cells (A7r5) were incubated with 1 micro M reduced MTR (non-fluorescent) and the MTR oxidation product (fluorescent) was quantified. Thirty-minute pretreatment with either diazoxide (200 micro M) or pinacidil (100 micro M), both potent mitochondrial K(ATP) channel openers, increased fluorescent intensity (FI) to 149 and 162 % of control (p < 0.05 for both), respectively, and the K(ATP) channel inhibitor 5-hydroxydecanoate (5 HD) blocked it. Valinomycin, a potassium-selective ionophore, raised FI to 156 % of control (p <: 0.05). However, 5 HD did not affect the valinomycin-induced increase in FI. Inhibition of mitochondrial electron transport (myxothiazol) or uncoupling of oxidative phosphorylation (dinitrophenol) also blocked either valinomycin- or diazoxide-induced increase in FI, and free radical scavengers prevented any diazoxide-mediated increase in fluorescence. Finally the diazoxide-induced increase in fluorescence was not blocked by the PKC inhibitor chelerythrine, but was by HMR 1883, a putative surface K(ATP) channel blocker. Thus opening of K(ATP) channels increases generation of ROS via the mitochondrial electron transport chain in vascular smooth muscle cells. Furthermore, a potassium-selective ionophore can mimic the effect of putative mitochondrial KATP channel openers. We conclude that potassium movement through KATP directly leads to ROS production by the mitochondria.

ATP-Binding Cassette Transporters↗
PubMed1996

Evidence against the association of the sulphonylurea receptor with endogenous Kir family members other than KATP in coronary vascular smooth muscle.

We used whole-cell patch clamp to record inward rectifier (KIR) and ATP-sensitive (KATP) K+ currents from pig coronary arterial myocytes. KIR currents were blocked by Ba2+ ions with a KD around 3 microM, but were unaffected by 10 microM glibenclamide, and only reduced 16% by 100 microM of the sulphonlyurea (n=4). In contrast, pinacidil-activated KATP currents were over 1000 times more sensitive to glibenclamide, being inhibited with a KD close to 100 nM (n=5). Our findings suggest that the sulphonylurea receptor (SUR) in these cells associates with the appropriate subunits of the Kir family to form KATP channels, but does not show promiscuous association with subunits that form the strong inward rectifier KIR.

ATP-Binding Cassette Transporters↗