| Abstrakt: |
Tumour-promoting phorbol esters (phorbol-12-myristate-13-acetate, PMA; phorbol-12,13-dibutyrate, PDBu) but not 4β-phorbol, activate protein kinase C. Using human platelets pre-labelled with quin2 or 32PO 4we examined the effects of these compounds on human platelet cytosolic free Ca 2+([Ca 2+] j) and on [ 32]phosphatidic acid ([ 32P]PtdOH). PMA and PDBu, but not 4β-phorbol inhibited thrombin-, PAF- and vasopressin-induced elevation of [Ca 2+], and [ 2+P]PtdOH formation. It is suggested that protein kinase C may act to terminate the transduction processes that link receptor occupancy to cellular activation. |
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