Species-related difference in the heart sarcolemmal enzyme activities

The sarcolemmal membranes were isolated by the hypotonic shock-LiBr treatment method from rat, guinea pig, rabbit, and dog hearts and their various biochemical activities were measured. The Mg2+-ATPase, Ca2+-ATPase, and 5'-nucleotidase were most active in rat heart homogenates as well as sarcolemmal membranes, whereas the adenylate cyclase and Na+, K+-ATPase were most active in guinea pig heart preparations. ATP-independent calcium binding activity of rat heart sarcolemma was the same as that of guinea pig heart membrane, whereas ATP-dependent calcium binding of rat heart preparation was negligible. Treatment of sarcolemma with 0.6 M KCl increased the adenylate cyclase and Na+, K+-ATPase activity in rat heart, but these activities were unaltered or decreased in other species. The gel electrophoretic pattern of protein bands and phospholipid composition of rat heart sarcolemma were different from those of guinea pig heart. Sarcolemma isolated from hearts by sucrose gradient method also showed species-dependent difference in the membrane-bound enzyme activities. These results have been interpreted to suggest species-related difference in calcium movements across sarcolemma and this may contribute to determining species-dependent difference in the regulation of myocardial calcium metabolism.