Enhancement of the ATP-sensitive K+ current by extracellular ATP in rat ventricular myocytes. Involvement of adenylyl cyclase-induced subsarcolemmal ATP depletion.
ATP-sensitive K+ (KATP) channels are present at high density in membranes of cardiac cells, where they regulate cardiac function during metabolic impairment. The present study analyzes the effects of extracellular ATP (ATPc), a P2-purinergic agonist that can be released under various conditions in the myocardial cell bed, on KATP current (IK-ATP) in rat ventricular myocytes. Under the whole-cell patch-clamp configuration at a physiological level of intracellular ATP, applying ATPc in the micromolar range did not activate IK-ATP. However, dialyzing the cell with a low-ATP (100 mumol/L) pipette solution elicited a slowly, quasilinearly increasing IK-ATP that was markedly enhanced by applying ATPe in the presence of a Purinergic antagonist. The effect was reversible on washing out the agonist. The IK-ATP enhancement was inhibited by cholera toxin treatment of the myocytes, suggesting that a Gs protein was involved to mediate the effect. Experiments on excised patches allowed us to exclude a membrane-delimited G protein-dependent pathway. Rather, the results suggested that ATPe activates the adenylyl cyclase, since its inhibition by 2'-deoxyadenosine 3'-monophosphate and SQ-22536, which respectively interact with the purine and catalytic site of the cyclase, strongly reduced the ATPe-induced IK-ATP enhancement, whereas neither compound affected IK-ATP in inside-out patches. Inhibition of cAMP-dependent protein kinase by protein kinase inhibitor peptide 5-24 did not alter the purinergic effect. The findings suggests that ATPe triggers the activation of adenylyl cyclase, which causes a subsarcolemmal ATP depletion sufficient to enhance IK-ATP as it develops during low-ATP dialysis of rat ventricular myocytes.
Babenko
A
A
INSERM U-390, Montpellier, France.
Vassort
G
G
D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D001578:Benzopyrans / Q000494:pharmacology; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000031:analogs & derivatives / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D019806:Cromakalim; D003838:Deoxyadenine Nucleotides / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005110:Extracellular Space / Q000737:chemistry*; D019204:GTP-Binding Proteins / Q000502:physiology; D006146:Guanidines / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006352:Heart Ventricles / Q000378:metabolism*; D008297:Male; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000494:pharmacology; D020110:Pinacidil; D015221:Potassium Channels / Q000378:metabolism*; D011758:Pyrroles / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D014475:Uncoupling Agents / Q000494:pharmacology
D000067956:Adenylyl Cyclase Inhibitors; D001578:Benzopyrans; D003838:Deoxyadenine Nucleotides; D004791:Enzyme Inhibitors; D006146:Guanidines; D010446:Peptide Fragments; D015221:Potassium Channels; D011758:Pyrroles; D014475:Uncoupling Agents; C518603:protein kinase inhibitor peptide (5-24); D019806:Cromakalim; C028191:2'-deoxy-3'-adenosine monophosphate; C017759:9-(tetrahydro-2-furyl)-adenine; D005576:Colforsin; C012804:carbonyl cyanide phenylhydrazone; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D020110:Pinacidil; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D019204:GTP-Binding Proteins; D000225:Adenine