Hypertrophied rat heart. New Na+, K+-ATPase-ouabain interactions in sarcolemma vesicles

The interactions between ouabain and sarcolemmal-bound Na+, K+-ATPase activity have been studied in rat left ventricles 70-130% hypertrophied by aortic constriction. Isolated sarcolemmal vesicles were 75-fold enriched in Na+, K+-ATPase and consisted in both impermeable inside-out vesicles and leaky material. The enzymatic activity was found to be almost completely inhibited at 10(-6) M ouabain instead of 2 X 10(-4) M in the normal left ventricle. In contrast with normal heart in which a Ca2+-free perfusion revealed a Na+, K+-ATPase activity highly sensitive to ouabain, in hypertrophied heart, a pretreatment plus or minus Ca2+ did not affect the high sensitivity form (half maximum inhibition with 0.8-2.2 X 10(-9) M ouabain). This enzyme form differed from the usual Na+, K+-ATPase activities by the absence of any detectable ouabain/K+ antagonism. The levels of 3H-ouabain binding, however, did not correlate with the levels of Na+, K+-ATPase inhibition. These results suggested that the Na+, K+-ATPase-ouabain interactions were altered in hypertrophied rat heart.