BDM DRIVES PROTEIN DEPHOSPHORYLATION AND INHIBITS ADENINE-NUCLEOTIDE EXCHANGE IN CARDIOMYOCYTES

Contractile dysfunction plays a key role in injury sustained by ischem ic myocardium at reperfusion, whereas interventions that impede hyperc ontracture enhance recovery. Ln permeabilized adult rat cardiomyocytes , the negative inotrope 2,3-butanedione monoxime (BDM; 10-50 mM) inhib ited rigor at low MgATP concentration but stimulated net ATP hydrolysi s. Hydrolysis was attenuated by H-7, kaempferol, chelerythrine, and ge nistein. Evidently BDM opposed phosphorylation of both serine/threonin e and tyrosine kinase target proteins, either directly or by enhancing protein phosphatase activity, in a futile cycle of ATP hydrolysis ind ependent of cross-bridge cycling. Although 20 mM BDM did not affect th e onset of rigor contracture in permeabilized cells at low MgATP, in i ntact cells exposed to the metabolic inhibitors cyanide and 2-deoxyglu cose rigor onset was accelerated, indicating that BDM increases ATP de pletion in quiescent cardiomyocytes. Conversely, in cells exposed to t he mitochondrial uncoupler carbonyl cyanide p-trifluoromethoxyphenylhy drazone, BDM delayed the onset of contracture and hence ATP depletion, consistent with an inhibition of adenine nucleotide movement across t he mitochondrial inner membrane. Such effects will limit the value of BDM as a cardioprotective agent at physiological temperature.