Phospholamban mediates the beta-adrenergic-enhanced Ca2+ uptake in mammalian ventricular myocytes.
To probe the molecular mechanism responsible for the relaxant effect of catecholamines in heart muscle, we studied the effect of a monoclonal antibody (2D12) against phospholamban in intact whole cell clamped guinea pig ventricular myocytes, in which intracellular Ca2+ transient and Ca2+ current were simultaneously measured. The antibody stimulated Ca2+ uptake in guinea pig ventricular sarcoplasmic reticular vesicles, shifting the apparent dissociation constant for activation by Ca2+ from 200 to 60 nM. The stimulatory effect of the antibody could be mimicked by the catalytic subunit of adenosine 3',5'-cyclic monophosphate-dependent kinase and could be blocked by phospholamban peptide 2-25. Dialysis of ventricular myocytes with the antibody enhanced the rate of uptake of Ca2+ and significantly suppressed the ability of isoproterenol to enhance the rate of uptake and release of Ca2+ by depolarizing pulses. These data suggest that not only is phosphorylation of phospholamban crucial in sequestration of Ca2+ by the sarcoplasmic reticulum, but that this process may account for the catecholamine-enhanced rate of Ca2+ uptake release in heart muscle.
Department of Physiology, University of Pennsylvania, Philadelphia 19104-6085.
J S
JS
Sham
L R
LR
Jones
M
M
Morad
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000276:immunology / Q000502:physiology*; D003956:Dialysis; D006168:Guinea Pigs; D006352:Heart Ventricles; D007545:Isoproterenol / Q000494:pharmacology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D000099211:Phospholamban
D000318:Adrenergic beta-Agonists; D000911:Antibodies, Monoclonal; D002118:Calcium; D002135:Calcium-Binding Proteins; D007545:Isoproterenol; D000099211:Phospholamban