A regulation of the level of phosphorylated phospholamban by inhibitor-1 in rat heart preparations in vitro.
Inhibitor-1 following phosphorylation by protein kinase A inhibits phosphoprotein phosphatase-1. We have found that in the rat heart inhibitor-1 is present only in the cytosolic fraction and that its phosphorylation in ventricular slices was increased by isoproterenol but not by isoproterenol and propranolol together. Cardiac microsomal phosphoprotein phosphatase activity, with added phosphorylase a as the substrate, was inhibited 33% by phosphorylated inhibitor-1. Phosphorylated inhibitor-1 decreased the dephosphorylation by exogenous phosphoprotein phosphatase-1 of phospholamban present in the sarcoplasmic reticulum membranes. These results suggest an interaction of cytoplasmic inhibitor-1 with either cytoplasmic or membrane-bound phosphoprotein phosphatase-1 with a subsequent effect on the level of phosphorylated phospholamban and the probable involvement of this interaction in the cardiac response to beta-adrenergic hormones.
Iyer
R B
RB
Department of Biochemistry, Mount Sinai School of Medicine, New York, NY 10029.
Koritz
S B
SB
Kirchberger
M A
MA
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D009206:Myocardium / Q000201:enzymology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D011506:Proteins / Q000502:physiology*; D011817:Rabbits; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000201:enzymology; D000099211:Phospholamban
D000251:Adenosine Triphosphatases; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D007545:Isoproterenol; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D011506:Proteins; D000099211:Phospholamban; C021042:protein phosphatase inhibitor-1