Reduced in vitro 32P incorporation into phospholamban-like protein of sarcolemma due to myocardial ischaemia in anaesthetized pigs.

The mechanism of Ca2+ overload production in ischaemia-reperfusion of the heart is unclear. The present study was designed to examine whether loss of second messenger (Ca2+ and cyclic AMP) control of sarcolemmal Ca2+ transport systems occurs during ischaemia. Ischaemic (1, 2 and 3 h duration) and non-ischaemic tissue samples were taken from the coronary-ligated porcine heart and a membrane fraction, enriched in sarcolemmal vesicles, was isolated. The membranes were phosphorylated using [gamma-32P] ATP in the presence of either cyclic AMP or Ca2+-calmodulin. The in vitro 32P incorporation into the electrophoretically separated phospholamban-like protein, became markedly reduced depending on the duration of ischaemia. The reduction could neither be attributed to factors as ischaemia-induced changes in membrane-bound kinase or phosphatase nor in situ phosphorylation of phospholamban. It is postulated that during ischaemia and reperfusion, a deficient control of the sarcolemmal Ca2+ pump by phospholamban-like protein may serve as a source of intracellular Ca2+ overload.