title: Differential effects of G-protein activators on 5-hydroxytryptamine and platelet-derived growth factor release from streptolysin-O-permeabilized human platelets.
abstract: In this paper we have used streptolysin O (SLO)-permeabilized human platelets to examine the G-protein(s) that control Ca2+-independent secretion from alpha and dense-core granules. As shown for electropermeabilized platelets, Ca2+ alone stimulated a concentration-dependent increase in 5-hydroxytryptamine (5-HT) (dense-core-granule marker) and platelet-derived growth factor (PDGF) (alpha-granule marker) release from the SLO-permeabilized cells. The EC50 values of Ca2+-dependent 5-HT and PDGF release were 5 microM and 10 microM respectively. Guanosine 5'-[gamma-thio]triphosphate (GTP[S]) (100 microM) stimulated Ca2+-independent release from both alpha and dense-core granules. In contrast, AlF4- had no effect on Ca2+-independent release from either alpha or dense-core granules. Neither GTP[S] nor AlF4- appeared to have a significant effect on Ca2+-dependent release from alpha and dense-core granules. GTP[S] can activate both heterotrimeric and low-molecular-mass G-proteins, whereas AlF4- activates only heterotrimeric G-proteins. Our results, therefore suggest that secretion in the human platelet is regulated by a small G-protein. Both GTP[S]- and Ca2+-dependent secretion were effected by extending the time between permeabilization with SLO and stimulation of secretion. GTP[S]-stimulated secretion from alpha and dense-core granules decreased rapidly after permeabilization. In contrast, Ca2+-dependent 5-HT and PDGF release ran down at a much lower rate. These observations indicate that GTP[S] and Ca2+ act through parallel pathways to stimulate secretion from SLO-permeabilized platelets.
authors.affiliation: Department of Internal Medicine, St. Louis University Health Sciences Center, MO 63104, USA.
authors.forename: P J
authors.initials: PJ
authors.lastname: Padfield
authors.forename: N
authors.initials: N
authors.lastname: Panesar
authors.forename: P
authors.initials: P
authors.lastname: Henderson
authors.forename: J J
authors.initials: JJ
authors.lastname: Baldassare
mesh_terms: D017607:Aluminum Compounds / Q000494:pharmacology; D001426:Bacterial Proteins; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D002463:Cell Membrane Permeability; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000378:metabolism; D004075:Diglycerides / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D005459:Fluorides / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006801:Humans; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D010712:Phosphatidic Acids / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism*; D013301:Streptolysins / Q000494:pharmacology
chemical_list: D017607:Aluminum Compounds; D001426:Bacterial Proteins; D004075:Diglycerides; D010712:Phosphatidic Acids; D010982:Platelet-Derived Growth Factor; D013301:Streptolysins; C025964:streptolysin O; D012701:Serotonin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004533:Egtazic Acid; D007770:L-Lactate Dehydrogenase; D019204:GTP-Binding Proteins; D005459:Fluorides; D002118:Calcium; C032311:aluminum fluoride