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PubMed · 6088288

Guanine nucleotides decrease the free [Ca2+] required for secretion of serotonin from permeabilized blood platelets. Evidence of a role for a GTP-binding protein in platelet activation.

R J Haslam·M M Davidson
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Abstract

Human platelets containing granule-bound [14C]serotonin were permeabilized, equilibrated at 0 degrees C with ATP and with various Ca2+ buffers and guanine nucleotides, and then incubated at 25 degrees C with or without a stimulatory agonist. Ca2+ alone induced the ATP-dependent secretion of [14C]serotonin (50% at a pCa of 5.1) but the sensitivity of secretion to Ca2+ was greatly enhanced by guanine nucleotides [6-fold by 100 microM GTP, 100-fold by 100 microM guanyl-5'-yl imidodiphosphate and greater than 500-fold by 100 microM guanosine 5'-O-(3-thiotriphosphate)] or by stimulatory agonists (10-fold by 2 units thrombin/ml and 4-fold by 1 microM 1-O-octadecyl-2-O-acetyl-sn-glyceryl-3-phosphorylcholine). When both GTP and a stimulatory agonist were added, they had synergistic effects on secretion. Cyclic GMP and GMP acted similarly to GTP. The effects of all these guanine nucleotides were inhibited by guanosine 5'-O-(2-thiodiphosphate), whereas those of stimulatory agonists were not. Our results demonstrate the presence in platelets of guanine nucleotide-dependent and independent mechanisms regulating the sensitivity of secretion to Ca2+.

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Blood PlateletsCalciumCell Membrane PermeabilityGTP-Binding ProteinsGuanine NucleotidesGuanosine TriphosphateHumansKineticsReceptors, Cell SurfaceSerotoninThrombinJournal ArticleResearch Support, Non-U.S. Gov't

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R J Haslam, M M Davidson. 1984-08-20. Guanine nucleotides decrease the free [Ca2+] required for secretion of serotonin from permeabilized blood platelets. Evidence of a role for a GTP-binding protein in platelet activation.. https://doi.org/10.1016/0014-5793(84)81084-4

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