Enzyme kinetics and the activation energy of (Na,K)-ATPase in ischaemic hearts: influence of the duration of ischaemia.

Hearts from male rats were incubated at 37 degrees C for variable periods of global ischaemia. Estimation of kinetic parameters of (Na,K)-ATPase at 37 degrees C in the presence of increasing concentrations of ATP revealed a significant decrease of Vmax in the first 15 minutes of ischaemia with further stabilization at the lowest level in 45-60 minutes of ischaemia. The changes in ATP binding site occurred later after 45 minutes of ischaemia as showed by the decrease of the Km value. As to the activation energy, there were no significant differences between control and ischaemic hearts.