Intracellular Ca2+ and delay of ischemia-induced electrical uncoupling in preconditioned rabbit ventricular myocardium.
OBJECTIVE
Short periods of ischemia and reperfusion alter myocardial Ca2+ handling and temporarily induce a mild increase of [Ca2+]i. We hypothesized that these alterations are involved in the cardioprotective mechanism of ischemic preconditioning, possibly via a Ca(2+)-dependent activation of protein kinase C (PKC).


RESULTS
In arterially perfused rabbit papillary muscles, we determined Ca2+ transients (indo 1) and indicators of the onset of irreversible ischemic damage, including [Ca2+]i rise, electrical uncoupling and contracture. We tested three protocols of ischemic preconditioning (1-3). In addition, the effects of infusion of staurosporine, a blocker of PKC (4), or glibenclamide, a blocker of K+ATP channels (5) were analyzed. Furthermore, pretreatment with phorbol 12-myrisate 13-acetate (PMA), an activator of PKC (6), or cyclopiazonic acid (CPA), an inhibitor of the SR Ca2+ pump (7) was tested. During periods of reperfusion in the preconditioning protocols, the duration of the Ca2+ transient and the diastolic Ca2+ level temporarily increased. Only if sustained ischemia was induced during these changes of the transients, cardioprotection was present. Similar alterations of the Ca2+ transient concurring with cardioprotection were induced by pretreatment with PMA as well as CPA. Staurosporine and glibenclamide antagonized the reperfusion-induced changes of the Ca2+ transients as well as cardioprotection. If reperfusion was extended until the Ca2+ transient had normalized, cardioprotection was also absent. Under all conditions tested, the diastolic Ca2+ elevation or the Ca2+ transient prolongation prior to sustained ischemia correlated with the postponement of ischemic injury.


CONCLUSIONS
A pre-ischemic mild increase of [Ca2-]i presents a common effector of preconditioning. Our data suggest that activation of PKC or opening of K+ATP channels may initiate the pathway leading to an alteration of Ca2+ metabolism and a protected status of the myocardium.
Dekker
L R
LR
Department of Clinical and Experimental Cardiology, Academic Medical Center, Amsterdam, The Netherlands. L.R.Dekker@AMC.UVA.NL
Coronel
R
R
VanBavel
E
E
Spaan
J A
JA
Opthof
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T
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005905:Glyburide / Q000494:pharmacology; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D007424:Intracellular Fluid / Q000378:metabolism*; D019157:Ischemic Preconditioning, Myocardial; D008297:Male; D017202:Myocardial Ischemia / Q000503:physiopathology / Q000517:prevention & control; D009206:Myocardium / Q000378:metabolism*; D010210:Papillary Muscles / Q000187:drug effects / Q000503:physiopathology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011817:Rabbits; D019311:Staurosporine / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D007211:Indoles; D015221:Potassium Channels; D000255:Adenosine Triphosphate; D011493:Protein Kinase C; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate; D005905:Glyburide; D002118:Calcium; C000543:cyclopiazonic acid