Abstract
1
The effects of lorcainide on the myocardial Mg2+‐dependent, Na+ and K+‐activated adenosine triphosphatase (Na+, K+‐ATPase) were compared in guinea‐pig heart preparations with those of ouabain, a specific inhibitor of the enzyme activity.
2
Both ouabain and lorcainide inhibited the microsomal Na+, K+‐ATPase activity in a concentration‐dependent fashion. Their inhibitory effective ranges were 0.05–100 μm and 0.15–125 μm respectively, and the concentrations for half maximal inhibition (IC50 values) were 2.1 ± 0.3 and 33.5 ± 7.3 μm, respectively.
3
In a second series of experiments, the combined effects of the two drugs on the enzyme activity were studied. In these experiments, lorcainide produced a concentration‐dependent potentiation of the inhibitory effects of ouabain on Na+, K+‐ATPase activity.
4
The present study demonstrates that lorcainide is a potent inhibitor of myocardial Na+, K+‐ATPase.