PRECONDITIONING IN RABBIT CARDIOMYOCYTES - ROLE OF PH, VACUOLAR PROTON ATPASE, AND APOPTOSIS

Ischemic preconditioning signals through protein kinase C (PKC) to pro tect against myocardial infarction. This protection is characterized b y diminished intracellular acidification, Acidification is also a feat ure of apoptosis, and several agents act to prevent apoptosis by preve nting acidification through activation of ion channels and pumps to pr omote cytoplasmic alkalinization. We characterized metabolic inhibitio n, recovery, and preconditioning through a PKC-dependent pathway in ca rdiomyocytes isolated from adult rabbit hearts, Preconditioning reduce d loss of viability assessed by morphology and reduced DNA nicking, Bl ockade of the vacuolar proton ATPase (VPATPase) prevented the effect o f preconditioning to reduce metabolic inhibition-induced acidosis, los s of viability, and DNA nicking, The beneficial effect of Na+/H+ excha nge inhibition, which is thought to be effective through reduced intra cellular Na+ and Ca++, was also abrogated by VPATPase blockade, sugges ting that acidification even in the absence of Na+/H+ exchange may lea d to cell death. We conclude that a target of PKC in mediating precond itioning is activation of the VPATPase with resultant attenuation of i ntracellular acidification during metabolic inhibition, Inhibition of the ''death protease,'' interleukin-l-beta converting enzyme or relate d enzymes, also protected against the injury that followed metabolic i nhibition, This observation, coupled with the detection of DNA nicking in cells subjected to metabolic inhibition, suggests that apoptotic c ell death may be preventable in this model of ischemia/reperfusion inj ury. (J. Clin. Invest. 1996. 97:2391-2398.)