Biomedical subjects

L L Friesen

Publications and source records attributed to L L Friesen.

3 recordsLinked to original sources

PubMed1985

Platelet protein phosphorylation.

As can be seen from this review, protein phosphorylation appears involved in both positive and negative regulation of platelets. To date, good evidence has been presented for the involvement of protein phosphorylation in the regulation of granule centralization (i.e. myosin light chain phosphorylation). It is probable that protein phosphorylation may also be involved in granule labilization, pseudopod formation and ATP synthesis. Protein phosphorylation in association with platelet activation appears mediated through calcium flux, in the case of myosin light chain phosphorylation, and through diglyceride or other substances in the case of 47P phosphorylation. A summary scheme is shown in Figure 1.

Actin Cytoskeleton↗

PubMed1985

The effects of 1-oleoyl-2-acetylglycerol on platelet protein phosphorylation and platelet ultrastructure.

1-oleoyl-2-acetylglycerol (OAG), an activator of protein kinase C and a synthetic diglyceride, was used in an investigation of the role of diglycerides in platelet stimulus-activation coupling. OAG (20-100 micrograms/ml) added to platelets resulted in rapid phosphorylation of the 47,000-dalton protein as well as a gradual dose dependent disappearance of alpha granules and dense bodies and the appearance of vacuolar structures containing remnants of granule matrix material. These morphologic changes occurred more slowly than the phosphorylation of 47K, which suggests that if these are related the phosphorylated 47K serves to activate some other mechanism, which is ultimately responsible for the changes observed. These results are most consistent with the role for the phosphorylation of 47K to promote granule labilization. Myosin light chain (MLC) phosphorylation also occurred. An absence of granule centralization suggests that MLC phosphorylation by protein kinase C may not trigger effective actin-myosin contraction.

Blood Platelets↗

PubMed1985

Protein phosphorylation and platelet secretion.

Platelet secretion in response to physiologic stimuli appears to result from the complementary stimulation of two processes--granule centralization and granule membrane fusion. Granule centralization is produced by actin-myosin contraction which is initiated by a movement of calcium ions into the cytoplasm. The calcium binds to calmodulin to form a complex which activates myosin light chain kinase to phosphorylate myosin light chain (MLC). Once phosphorylated in this fashion, actin-myosin contraction occurs. Granule membrane fusion can be produced selectively by phorbol myristate acetate and oleoyl-acetyl diglyceride, both of which activate protein kinase C. Phosphorylation of a 47,000 dalton intracellular protein (47K) by protein kinase C may be critical to granule membrane fusion. The mechanism of action of 47K is presently unknown. The combined phosphorylation of MLC and 47K in response to most physiologic agonists which cause granule secretion, and the synergistic effects on granule secretion of agents which independently stimulate MLC and 47K phosphorylation, suggests secretion usually results from the interaction of granule centralization and granule membrane fusion.

Actin Cytoskeleton↗