The effect of alpha-adrenergic agents and protein kinase C activators on protein phosphorylation in isolated guinea pig hearts.
The incorporation of [32P]Pi into sarcolemmal, sarcoplasmic reticular and myofibrillar proteins was studied in Langendorff-perfused guinea pig hearts treated with the alpha-agonist norepinephrine or with protein kinase C activators (phorbol 12-myristate 13-acetate (PMA) or 1,2-dioctanoylglycerol (D8G]. Norepinephrine was administered in the presence of propranolol and atropine, while the protein kinase C activators (PMA and D8G) were infused in the presence of propranolol, atropine and prazosin. Examination of 32P-incorporation into the various cardiac proteins revealed that there were no significant increases in the degree of phosphorylation of the: (1) 15 kDa sarcolemmal protein; (2) phospholamban in sarcoplasmic reticulum; and (3) troponin I and C protein in the myofibrils. In parallel control studies, stimulation of beating guinea pig hearts by isoproterenol was associated with a 4-5-fold increase in 32P-incorporation into phospholamban and troponin I and about a 2-fold increase in 32P-incorporation into C protein and the 15 kDa sarcolemmal protein. These findings indicate that the major cardiac regulatory phosphoproteins, which have been reported to serve as substrates for protein kinase C in vitro, are not phosphorylated by the same enzyme in perfused, beating guinea pig hearts.
Edes
I
I
2nd Department of Medicine, Albert Szent-Gyorgyi Medical University, Szeged, Hungary.
Talosi
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L
Kranias
E G
EG
D000818:Animals; D004075:Diglycerides / Q000494:pharmacology*; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D009206:Myocardium / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology*; D010704:Phorbols / Q000494:pharmacology*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000187:drug effects*; D011506:Proteins / Q000378:metabolism*; D012508:Sarcolemma / Q000187:drug effects; D012519:Sarcoplasmic Reticulum / Q000187:drug effects
D004075:Diglycerides; D010704:Phorbols; D011506:Proteins; C044295:1,2-dioctanoylglycerol; D011493:Protein Kinase C; D009638:Norepinephrine