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

Objective: Although several studies have shown that activation of protein kinase C (PKC) plays an important role in protection through ischemic preconditioning, little is known about the effects of direct PKC activation on the course of ischemia-reperfusion injury. The aim of this study was to analyse the effects of a pretreatment with the PKC activator 1,2-dioctanoyl-sn-glycerol (1,2DOG). Methods: Isolated adult Wistar rat cardiomyocytes were exposed to 80 min of simulated ischemia (anoxia, pH(o)6.4) and 20 min of reoxygenation (pH(o)7.4). Cytosolic Ca2+ (fura-2), cytosolic pH (BCECF), Mg2+ (Mg-fura-2), lactate and cell length were measured and compared between control cells and cells treated with 20 mu mol/l 1,2DOG before anoxia (10 min treatment and 10 min wash out). Results: 1,2DOG-pretreatment delayed the time to extreme ATP depletion, but had no effect on lactate production and cytosolic pH. The accumulation of cytosolic Ca2+ was markedly accelerated in pretreated cells that developed rigor shortening, but reoxygenation-induced hypercontracture was significantly reduced. 1,2DOG, therefore, completely abolished Ca2+-dependence of hypercontracture. The effects of pretreatment were 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 reoxygenation-induced hypercontracture independent of anoxic changes in cytosolic Ca2+ and pH. (C) 1999 Elsevier Science B.V. All rights reserved.