IMPACT OF PERIODIC HYPOXIC ADAPTATION ON THE CALCIUM-PUMP OF THE CARDIAC SARCOPLASMIC-RETICULUM AND ITS RESISTANCE TO ENDOGENOUS DAMAGING FACTORS

The adaptation of rats to periodic ''altitude'' hypoxia in the altitud e chamber (6 hour daily at an altitude of 5000 m during a month) led t o increased activity of the Ca2+ pump in the myocardial sarcoplasmic r eticulum, which was associated with lower K(d) values and higher calci um transport V(max). When a cardiac homogenate was kept at 4-degrees-C , autolysis resulted in a decrease in Ca2+ pump activity (which was mo re rapid in adapted animals than in the controls) and an equal increas e in the levels of free calcium in the homogenates in the two series o f experiments. The approximate data were obtained when a homogenate wa s incubated at 37-degrees-C, but when it was incubated at 4-degrees-C, the rate of Ca2+-pump inactivation decreased 20-fold. Incubation in t he presence of free radical oxidative inductors (Fe2+ ascorbate) led t o high resistance of myocardial Ca2+-pump in the adapted rats. The pap er discusses the causes of myocardial Ca2+-pump activation in periodic hypoxic adaptation and the mechanisms for its increased resistance to active oxygen, as well as their role in the cardioprotective effect o f the adaptation.