METABOLIC RECOVERY OF ISOLATED ADULT-RAT CARDIOMYOCYTES AFTER ENERGY DEPLETION - EXISTENCE OF AN ATP THRESHOLD

The question was investigated whether cardiomyocytes can be resuscitat ed after extreme energy depletion, i.e. after loss of ATP >70%. Isolat ed ventricular cardiomyocytes of the adult rat were exposed to metabol ic inhibition with dinitrophenol and cyanide (DNP 0.2 mM: KCN 2 mM). A fter rapid energy depletion, cells were ''reoxygenated'' by wash-out o f DNP and KCN. Intracellular calcium, cell length, ATP and creatine ph osphate (CrP) of the cardiomyocytes were monitored. Metabolic inhibiti on resulted in a depletion of the stores of ATP and CrP by more than 9 5% of the normoxic values and caused a cytosolic Ca2+ overload. Parame ters of metabolic recovery were: (i) resynthesis of CrP; (ii) recovery of a normal cytosolic Ca2+ control; and (iii) the elicitation of ener gy-dependent hypercontracture. ''Reoxygenation'', i.e. wash-out of met abolic inhibitors, reactivated oxidative phosphorylation. Consecutivel y, CrP levels recovered to 76.0 +/- 7.3%, ATP levels recovered to 10.4 +/- 2.3% (means +/- S.D., n = 10) of the initial normoxic values, a n ormoxic intracellular calcium level was re-established and hypercontra cture was elicited. Prolongation of metabolic inhibition with KCN (2 m M) or inhibition of the Na+/K+ pump with ouabain (0.5 mM) disabled the cardiomyocytes to recover from cytosolic Ca2+ overload and prevented hypercontracture. It is concluded that even after extensive energy dep letion metabolic resuscitation of the myocardial cell remains possible and a critical range of ATP for recovery i.e. a ''threshold'' of a 70 % loss of ATP, does not exist. (C) 1998 Academic Press.