Reversible phosphorylation of microsomal membranes by cyclic AMP enhances calcium uptake, suggesting a key regulatory mechanism for calcium transport in cardiac microsomes.
The role of cyclic adenosine 3', 5'-monophosphate (AMP) in the control of microsomal calcium ion (Ca 2+ ) transport was studied in microsomes prepared from rabbit heart. These cardiac microsomes contained intrinsic cyclic AMP-dependent protein kinase activity that phosphorylated serine residues in a microsomal protein component with a molecular weight of about 20,000 (determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis). Intrinsic phosphoprotein phosphatase activity of the microsomal membranes resulted in rapid dephosphorylation of these residues. Microsomes phosphorylated in the presence of 1 x 10 -6 M cyclic AMP exhibited enhanced Ca 2+ uptake. We conclude that reversible phosphorylation of microsomal membranes may be an important mechanism for regulation of microsomal Ca 2+ transport by cyclic AMP.
LaRaia et al. (Thu,) studied this question.