Acidosis alters the phosphorylation of Ser16 and Thr17 of phospholamban in rat cardiac muscle.
The effect of acidosis on the phosphorylation of Ser16 and Thr17 of phospholamban in rat cardiac muscle has been investigated using phosphorylation-site-specific antibodies to this protein. Ventricular myocytes were stimulated at 0.5 Hz for 5 min, in either control (pH 7.4) or acid (pH 6.5) physiological salt solution, in the absence or presence of isoprenaline. Site-specific phosphorylation of phospholamban was determined by Western blotting. Acidosis reduced phosphorylation of Ser16 in the absence of isoprenaline, but did not alter the isoprenaline-induced phosphorylation of Ser16. In contrast, acidosis increased Thr17 phosphorylation in the absence and presence of isoprenaline. Buffering intracellular Ca2+ ([Ca2+]i) with BAPTA inhibited the increase in Thr17 phosphorylation during acidosis but had no effect on Ser16 phosphorylation. We conclude that acidosis can alter the phosphorylation of Ser16 and Thr17 by inhibition of protein kinase A, and by an acidosis-induced increase in [Ca2+]i and the subsequent activation of a Ca2+/calmodulin-dependent protein kinase, respectively. The possible effect of these changes in phosphorylation on the activity of the Ca2+-ATPase of the cardiac sarcoplasmic reticulum during acidosis is discussed.
Hulme
J T
JT
Department of Physiology, University of Leeds, Leeds, LS2 9JT, UK.
Colyer
J
J
Orchard
C H
CH
D000138:Acidosis / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D006352:Heart Ventricles; D008297:Male; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D000099211:Phospholamban
D002118:Calcium; D002135:Calcium-Binding Proteins; D002614:Chelating Agents; D004533:Egtazic Acid; D000099211:Phospholamban; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester