SUR2A C-terminal fragments reduce KATP currents and ischaemic tolerance of rat cardiac myocytes.
C-terminal fragments of the sulphonylurea receptor SUR2A can alter the functional expression of cloned ATP-sensitive K(+) channels (K(ATP)). To investigate the protective role of K(ATP) channels during metabolic stress we transfected SUR2A fragments into adult rat cardiac myocytes. A fragment comprising residues 1294-1358, the A-fragment, reduced sarcolemmal K(ATP) currents by over 85% after 2 days (pinacidil-activated current densities were: vector alone 7.04 +/- 1.22; and A-fragment 0.94 +/- 0.07 pA pF(-1), n= 6,6, P < 0.001). An inactive fragment (1358-1545, current density 6.30 +/- 0.85 pA pF(-1), n= 6) was used as a control. During metabolic inhibition (CN and iodoacetate) of isolated myocytes stimulated at 1 Hz, the A-fragment delayed action potential shortening and contractile failure, but accelerated rigor contraction and increased Ca(2+) loading. On reperfusion, A-fragment-transfected cells also showed increased intracellular Ca(2+) and the proportion of cells recovering contractile function was reduced from 40.0 to 9.5% (P < 0.01). The protective effect of pretreatment with 2,4-dinitrophenol, measured from increased functional recovery and reduced Ca(2+) loading, was abolished by the A-fragment. Our data are consistent with a role for K(ATP) channels in causing action potential failure and reduced Ca(2+) loading during metabolic stress, and with a major role in protection by preconditioning. The effects of the A-fragment may arise entirely from reduced expression of the sarcolemmal K(ATP) channel, but we also discuss the possibility of mitochondrial effects.
Rainbow
R D
RD
Department of Cell Physiology and Pharmacology, University of Leicester, PO Box 138, Leicester LE1 9HN, UK.
Lodwick
D
D
Hudman
D
D
Davies
N W
NW
Norman
R I
RI
Standen
N B
NB
D019297:2,4-Dinitrophenol / Q000494:pharmacology; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000502:physiology*; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000502:physiology; D002478:Cells, Cultured; D004558:Electric Stimulation; D004594:Electrophysiology; D066298:In Vitro Techniques; D054086:KATP Channels; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009200:Myocardial Contraction / Q000187:drug effects; D017202:Myocardial Ischemia / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000235:genetics / Q000502:physiology; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D015221:Potassium Channels / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D011955:Receptors, Drug / Q000235:genetics / Q000502:physiology*; D012508:Sarcolemma / Q000187:drug effects / Q000378:metabolism; D064233:Sulfonylurea Receptors; D014162:Transfection
D018528:ATP-Binding Cassette Transporters; D000963:Antimetabolites; D054086:KATP Channels; D010446:Peptide Fragments; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; C092520:uK-ATP-1 potassium channel; D019297:2,4-Dinitrophenol; D002118:Calcium