Sarcolemmal phospholamban is phosphorylated in isolated rat hearts perfused with isoprenaline.

Phosphorylation of phospholamban in cardiac sarcolemma is implicated in the increased influx of Ca2+ through the slow calcium channel induced by catecholamines. A method is described for the preparation of highly purified sarcolemmal vesicles from rat heart, and this has been used to examine the phosphorylation of phospholamban in 32Pi-perfused rat hearts. Phospholamban phosphorylation is increased 3-fold after 30 s of perfusion with 0.1 microM isoprenaline. The time course of this increase precedes the inotropic response by 5-10 s.