ENZYME-KINETICS AND THE ACTIVATION-ENERGY OF (NA,K)-ATPASE IN ISCHEMIC HEARTS - INFLUENCE OF THE DURATION OF ISCHEMIA

Hearts from male rats were incubated at 37 degrees C for variable peri ods of global ischaemia. Estimation of kinetic parameters of (Na,K)-AT Pase at 37 degrees C in the presence of increasing concentrations of A TP revealed a significant decrease of V-max in the first 15 minutes of ischaemia with further stabilization at the lowest level in 45-60 min utes of ischaemia. The changes in ATP binding site occurred later afte r 45 minutes of ischaemia as showed by the decrease of the K-m value. As to the activation energy, there were no significant differences bet ween control and ischaemic hearts.