Previous studies have shown that
ischemia-reperfusion (I/R) injury is associated with cardiac dysfunction and changes in sarcolemmal Na(+)-K(+)-
ATPase subunits and activity. This study was undertaken to evaluate the role of
proteases in these alterations by subjecting rat hearts to different times of global
ischemia, as well as reperfusion after 45 min of
ischemia. Decreases in Na(+)-K(+)-
ATPase activity at 30-60 min of global
ischemia were accompanied by augmented activities of both
calpain and
matrix metalloproteinases (
MMPs) and depressed
protein content of β(1)- and β(2)-subunits, without changes in α(1)- and α(2)-subunits of the
enzyme. Compared with control values, the activities of both
calpain and MMP-2 were increased, whereas the activity and
protein content for all subunits of Na(+)-K(+)-
ATPase were decreased upon reperfusion for 5-40 min, except that α(1)- and α(2)-subunit content was not depressed in 5 min I/R hearts.
MDL28170, a
calpain inhibitor, was more effective in attenuating the I/R-induced alterations in cardiac
contracture, Na(+)-K(+)-
ATPase activity, and α(2)-subunit than
doxycycline, an
MMP inhibitor. Incubation of control sarcolemma preparation with
calpain, unlike MMP-2, depressed Na(+)-K(+)-
ATPase activity and decreased α(1)-, α(2)-, and β(2)-subunits, without changes in the β(1)-subunit. These results support the view that activation of both
calpain and MMP-2 are involved in depressing Na(+)-K(+)-
ATPase activity and degradation of its subunits directly or indirectly in hearts subjected to I/R injury.