AJP - Heart and Circulatory Physiology, Vol 234, Issue 5 508-H514, Copyright © 1978 by American Physiological Society
Role of cyclic AMP in rat aortic microsomal phosphorylation and calcium uptake
R. C. Bhalla, R. C. Webb, D. Singh and T. Brock
The role of adenosine 3',5'-monophosphate (cyclic AMP)-dependent membrane
phosphorylation in the regulation of microsomal calcium transport in rat
aortic smooth muscle was studied. Cyclic AMP-dependent protein kinase
augmented the phosphorylation of serine residues in a microsomal protein
component with a molecular weight of about 44,000 (determined by sodium
dodecyl sulfate-polyacrylamide gel electrophoresis) and the majority of 32P
incorporation was in serine residue(s). The phosphorylated protein had
stability characteristics of a phosphoester. The phosphorylated substrate
was not extracted from the trichloroacetic acid (TCA) precipitate with
organic solvents or by suspension in hot TCA; and the demonstrated
hydroxylamine insensitivity suggested that the substrate was not lipid or
nucleic acid. Intrinsic phosphoprotein phosphatase cleaved the labeled
phosphate from the cyclic AMP-stimulated microsomes in the first 5 min of
incubation. Microsomes phosphorylated in the presence of 1 micron cyclic
AMP or 1 micron cyclic AMP plus 0.1 mg/ml protein kinase exhibited enhanced
calcium uptake. We suggest that reversible phosphorylation of microsomal
membranes may play an important role in the regulation of aortic microsomal
calcium transport by cyclic AMP.
