Role of Ca(2+) and protein kinase C in the serotonin (5-HT) transport in human platelets

• Published in: Cell calcium (Edinburgh) 2002-05, Vol.31 (5), p.235
• Main Authors: Turetta, L, Bazzan, E, Bertagno, K, Musacchio, E, Deana, R
• Format: Article
• Language: English
• Subjects: Acridine Orange - pharmacology; Blood Platelets - drug effects; Blood Platelets - enzymology; Calcium - metabolism; Calcium Signaling - drug effects; Calcium Signaling - physiology; Carrier Proteins - drug effects; Carrier Proteins - metabolism; Cell Membrane - drug effects; Cell Membrane - enzymology; Cells, Cultured; Chelating Agents - pharmacology; Cytosol - drug effects; Cytosol - metabolism; Enzyme Inhibitors - pharmacology; Humans; Protein Kinase C - antagonists & inhibitors; Protein Kinase C - metabolism; Protein Synthesis Inhibitors - pharmacology; Reserpine - pharmacology; Serotonin - metabolism; Serotonin Plasma Membrane Transport Proteins
• ISSN: 0143-4160
• DOI: 10.1016/S0143-4160(02)00052-0

Accumulation of serotonin (5-HT) into human platelets was not affected by the presence of the extra-cellular calcium chelator EGTA, while decreased by platelet incubation with the membrane permeant chelator BAPTA-AM. Serotonin uptake also diminished upon platelet exposure to EGTA/thapsigargin or EGTA/ionomycin which increased the cytosolic [Ca(2+)] to levels lower than those inducing secretion of dense granules. The latter inhibition depended in part on changes of intra-granular pH, since the accumulation of acridine orange, which is driven into the dense granules by the intra-granular acid pH gradient, was slightly decreased in the presence of EGTA/thapsigargin. These compounds also inhibited the 5-HT uptake in platelets pre-incubated with reserpine and bafilomycin that prevent 5-HT from entering into the dense granules. Inhibitors of protease, protein phosphatase, Na(+)/H(+) exchanger or ciclo-oxygenase activities did not modify the serotonin accumulation. Addition of EGTA/thapsigargin to reserpine-treated, [(14)C]5-HT-loaded, platelets caused an imipramine-insensitive release of labelled serotonin. This release was reduced by both BAPTA-AM or protein kinase C inhibitor bisindoylmaleimide (GF). The latter compound, either alone or together with EGTA/thapsigargin, inhibited the 5-HT accumulation in reserpine-treated platelets. It is concluded that both cytosolic [Ca(2+)] and protein kinase C are involved in the regulation of the plasma membrane 5-HT transport.