24] Reconstitution of calcium pumping of cardiac sarcoplasmic reticulum

Abstract

This chapter describes the reconstitution of cardiac SR transport function, which has provided new insight into the nature of the modulation of Ca 2+ transport. The β-adrenergic action of catecholamines on heart muscle is, in part, explained by modulation of Ca 2+ fluxes by way of the action of their intracellular second messengers, such as cAMP and Ca 2+ itself. At the level of cardiac sarcoplasmic reticulum (SR), the Ca 2+ -pump, which transports Ca 2+ from the cytoplasm into the lumen of the SR, can be modulated by cAMP and Ca 2+ -calmodulin. In cardiac SR, phospholamban is phosphorylated by adding catalytic subunit of cAMP-dependent protein kinase or via an intrinsic Ca 2+ -calmodulin-dependent protein kinase. Phospholamban in the reconstituted vesicles is also phosphorylated by the catalytic subunit of cAMP-dependent protein kinase to about the same extent as that in the original vesicles. In the original cardiac SR, it is known that a significant stimulation of Ca 2+ loading is observed when phospholamban is phosphorylated, by way of a decrease in the Ca 2+ concentration for the half-maximal Ca 2+ -loading rate (Kc a ).