title: Effect of phorbol esters and diacylglycerols on calcium transport by human platelet membranes.
abstract: The effects of phorbol esters and diacylglycerols on Ca2+ transport in isolated human platelet membranes were determined. Phorbol 12-myristate 13-acetate (PMA) stimulated Ca2+-ATPase activity in crude and purified internal platelet membranes approximately 2-fold with half-maximal stimulation occurring at 10 nM. Dilauroylglycerol also stimulated Ca2+-ATPase activity half-maximally at a concentration of 7.5 microM, but dioctanoylglycerol was without effect at up to 30 microM. PMA also inhibited Ca2+ uptake when added before or after commencement of ATP-dependent transport. PMA (25 nM) doubled the rate of Ca2+ efflux from passively loaded membranes in the absence of ATP. No protein kinase C activity was detected in crude or purified membranes by histone phosphorylation or endogenous protein phosphorylation assays. These results suggest that PMA and dilauroylglycerol stimulate Ca2+-ATPase activity and inhibit ATP-dependent Ca2+ transport by increasing the permeability of the membranes to Ca2+.
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000097:blood*; D002462:Cell Membrane / Q000378:metabolism; D004075:Diglycerides / Q000494:pharmacology*; D005989:Glycerides / Q000494:pharmacology*; D006657:Histones / Q000378:metabolism; D006801:Humans; D010703:Phorbol Esters / Q000494:pharmacology*; D010766:Phosphorylation
chemical_list: D004075:Diglycerides; D005989:Glycerides; D006657:Histones; D010703:Phorbol Esters; D002118:Calcium