The effect of verapamil on ischaemia-induced changes to the sarcolemma.

The effect of verapamil on sarcolemmal activities of sarcolemmal fragments isolated from aerobically perfused (control) and ischaemic rat hearts was examined. Adding verapamil to the perfusate of aerobically perfused hearts for 75 min enhanced some of the sarcolemmal activities; Na+-K+ ATPase (31%), K+ stimulated phosphatase (31%) and Na+-Ca2+ exchange rate (46%). Adding verapamil directly to the enzymatic incubation media, or to the cardiac homogenate prior to sarcolemmal isolation did not alter these activities, suggesting that these changes are dependent upon addition of verapamil to the intact system. Addition of verapamil to hearts 15 min prior to a 60 min ischaemic episode maintained a number of sarcolemmal activities close to those obtained after aerobic perfusion. Na+-K+ ATPase activity and Na+-Ca2+ exchange received a relative protection while K+ stimulated phosphatase activity was not protected. 5'-nucleotidase activity was completely protected against ischaemia-induced depression. The mechanism whereby verapamil induces these changes in sarcolemmal enzymatic activities is unclear but its ability to maintain these activities at or near normal levels may contribute to its ability to protect against the deleterious effects of ischaemia.