Inhibitory action of opioid peptides on ouabain-sensitive Na +-K + and Ca 2+-dependent ATPase activities in bovine cardiac sarcolemma

Abstract

The present study demonstrates that morphine (10 −6 and 10 −5 M), methionine-enkephalin or leucine-enkephalin (10 −10, 10 −8 and 10 −6 M) were able to inhibit significantly, in a dose-dependent manner, both the sarcolemmal Ca 2+-dependent ATPase and the ouabain-sensitive Na +-K + ATPase activities. The inhibitory action of these opioids on the two ATPases was not antagonized by preincubation with naloxone (10 −6 M). Naloxone alone (10 −8, 10 −6 and 10 −5 M) did not affect both the sarcolemmal Ca 2+-dependent ATPase and the ouabain-sensitive Na +-K + ATPase activities. Heat-denatured methionine-enkephalin (10 −6 M) or leucine-enkephalin (10 −6 M) also unaffected both the ATPases. The possibility is also discussed that opioid peptides may regulate myocardial contractility by modulating the movement of ions across the heart sarcolemma.