Pharmacological activation of plasma-membrane KATP channels reduces reoxygenation-induced Ca(2+) overload in cardiac myocytes via modulation of the diastolic membrane potential.
1. The opening of cardiac plasma-membrane ATP-sensitive K(+) channels (pmK(ATP)) can protect the heart against ischaemia/reperfusion injury. We recently demonstrated that the resting membrane potential (E(m)) of ventricular myocytes strongly modulates reoxygenation-induced Ca(2+) overload. This led to the hypothesis that activation of pmK(ATP) can influence the extent of chemically induced hypoxia (CIH)/reoxygenation Ca(2+) overload via hyperpolarization of the diastolic membrane potential of ventricular myocytes. 2. The membrane potential (E(m)) of isolated rat myocytes was determined using the perforated patch-clamp technique and DiBac(4)(3) imaging. Intracellular Ca(2+) ([Ca(2+)](i)) was monitored using FURA-2 imaging. 3. CIH/reoxygenation caused a significant depolarization of E(m) and a substantial increase in [Ca(2+)](i). The K(ATP) opener pinacidil (100 microm) and the pmK(ATP) opener P-1075 (100 microm) hyperpolarized the E(m) of normoxic myocytes. Pinacidil (100 microm) and P-1075 (10 and 100 microm), applied during reoxygenation, hyperpolarized E(m) and prevented reoxygenation-induced increases in [Ca(2+)](i). 4. Myocyte hypercontracture and death increased in parallel with an E(m) depolarization of 10-15 mV and increases in [Ca(2+)](i). Under these conditions, the selective pmK(ATP) channel inhibitor HMR 1098 further depolarized myocyte membrane potential and increased hypercontracture. 5. In conclusion, activation of pmK(ATP) channels can prevent CIH/reoxygenation-induced Ca(2+) overload via a mechanism that is dependent on hyperpolarization of diastolic membrane potential. Hyperpolarization toward normal resting membrane potential favours the Ca(2+) extrusion mode of Na(+)/Ca(2+) exchange.
Department of Physiology and Biophysics, University of Calgary, Alberta, Canada.
István
I
Baczkó
Wayne R
WR
Giles
Peter E
PE
Light
D000818:Animals; D001463:Barbiturates; D001549:Benzamides / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015687:Cell Hypoxia; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004558:Electric Stimulation; D005456:Fluorescent Dyes; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D066298:In Vitro Techniques; D007555:Isoxazoles; D008564:Membrane Potentials / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D020110:Pinacidil / Q000494:pharmacology; D020442:Poloxamer / Q000494:pharmacology; D024661:Potassium Channels, Inwardly Rectifying / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011339:Probenecid / Q000494:pharmacology; D051381:Rats
D001463:Barbiturates; D001549:Benzamides; D005456:Fluorescent Dyes; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D007555:Isoxazoles; C484274:KCNJ5 protein, human; D024661:Potassium Channels, Inwardly Rectifying; D020442:Poloxamer; C052795:bis(1,3-dibutylbarbiturate)trimethine oxonol; D020110:Pinacidil; C410297:HMR 1098; D011339:Probenecid; D002118:Calcium