Pretreatment with PKC activator protects cardiomyocytes against reoxygenation-induced hypercontracture independently of Ca2+ overload

Objective: Although several studies have shown that activation of protein k inase C (PKC) plays an important role in protection through ischemic precon ditioning, little is known about the effects of direct PKC activation on th e course of ischemia-reperfusion injury. The aim of this study was to analy se the effects of a pretreatment with the PKC activator 1,2-dioctanoyl-sn-g lycerol (1,2DOG). Methods: Isolated adult Wistar rat cardiomyocytes were ex posed to 80 min of simulated ischemia (anoxia, pH(o)6.4) and 20 min of reox ygenation (pH(o)7.4). Cytosolic Ca2+ (fura-2), cytosolic pH (BCECF), Mg2+ ( Mg-fura-2), lactate and cell length were measured and compared between cont rol cells and cells treated with 20 mu mol/l 1,2DOG before anoxia (10 min t reatment and 10 min wash out). Results: 1,2DOG-pretreatment delayed the tim e to extreme ATP depletion, but had no effect on lactate production and cyt osolic pH. The accumulation of cytosolic Ca2+ was markedly accelerated in p retreated cells that developed rigor shortening, but reoxygenation-induced hypercontracture was significantly reduced. 1,2DOG, therefore, completely a bolished Ca2+-dependence of hypercontracture. The effects of pretreatment w ere fully abolished with 1 mu mol/l bisindolylmaleimide (PKC inhibitor). We conclude that PKC preactivation leads to (1) reduction of energy demand, ( 2) acceleration of Ca2+ overload during anoxia and (3) prevention of reoxyg enation-induced hypercontracture independent of anoxic changes in cytosolic Ca2+ and pH. (C) 1999 Elsevier Science B.V. All rights reserved.