Role of myosin phosphorylation in contractility of a platelet aggregate.
The relationship between tension and myosin 20,000-Da light chain phosphorylation in intact nonmuscle cells was investigated using a preparation of thrombin-activated, irreversibly aggregated platelets known as the platelet strip. Steady-state levels of tension generated by the platelet strip were found to be linearly related to the level of myosin phosphorylation. This relationship was observed during dose-dependent relaxation induced by the adenylate cyclase activators prostaglandin (PG) E1 and PGI2, and during contraction induced by ADP, epinephrine, and the prostaglandin endoperoxide analogue U-46619, which did not appreciably alter the basal level of adenosine 3',5'-cyclic monophosphate in the preparation. The fully relaxed platelet strip, in the absence of external Ca2+, was associated with a level of 12% light chain phosphorylation, which increased to 72% on maximal contraction. During both relaxation and contraction, changes in myosin phosphorylation were also found to precede or coincide with tension changes. Furthermore, steady-state contraction induced by ADP was associated with a maintained elevation in the level of myosin phosphorylation. These results support the concept that myosin phosphorylation is an important regulatory mechanism for contractility in platelets.
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000527:Alprostadil; D001792:Blood Platelets / Q000187:drug effects; D000242:Cyclic AMP / Q000097:blood; D004533:Egtazic Acid / Q000494:pharmacology; D011464:Epoprostenol / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D009218:Myosins / Q000097:blood*; D010766:Phosphorylation; D010974:Platelet Aggregation / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology; D011458:Prostaglandins E / Q000494:pharmacology; D013314:Stress, Mechanical
D011458:Prostaglandins E; D004533:Egtazic Acid; D000244:Adenosine Diphosphate; D011464:Epoprostenol; D000242:Cyclic AMP; D009218:Myosins; D000527:Alprostadil; D011188:Potassium