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MH Werner and YA Hannun
Department of Medicine, Duke University School of Medicine, Durham, NC
27710.
An important mechanism of platelet regulation is the formation of the
second messenger diacylglycerol (DAG) and the activation of protein kinase
C (PKC). Our previous studies suggested that the DAG/PKC pathway plays an
important role in the induction of secretion and secondary aggregation
rather than the earlier events of shape change and primary aggregation. We
therefore examined the hypothesis that the delayed effects of PKC on
platelets may result from delayed accumulation of DAG. The kinetics of DAG
formation in human platelets were determined. When platelets were
stimulated with gamma-thrombin, the largest phase of DAG accumulation was
delayed for 0.6 to 0.8 minutes and DAG mass levels remained elevated for at
least 2 minutes. In platelets stimulated with collagen, DAG accumulation
was delayed for 1.0 to 1.2 minutes and DAG mass levels remained elevated
for at least 3 minutes after stimulation. Sustained DAG production was also
associated with sustained activation of PKC as monitored by phosphorylation
of the 40- Kd substrate of PKC. The physiologic significance of delayed DAG
accumulation was investigated using the cell-permeable DAG analog,
dioctanoylglycerol (diC8). In synergy with subthreshold gamma-thrombin or
collagen, exogenous diC8 reconstituted platelet activation. The optimal
timing of addition of diC8 was 0.5 minutes after stimulation with
gamma-thrombin or collagen. These kinetics were similar to those of
endogenous DAG accumulation. These studies underscore the importance of a
delayed accumulative phase of DAG generation as a mechanism controlling the
onset of platelet secretion and irreversible aggregation.
This article has been cited by other articles:
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| Copyright © 1991 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||
