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Cytoplasmic free Ca 2+ in human platelets: Ca 2+ thresholds and Ca‐independent activation for shape‐change and secretion
Author(s) -
Rink T.J.,
Smith S.W.,
Tsien R.Y.
Publication year - 1982
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(82)81234-9
Subject(s) - ionomycin , ionophore , exocytosis , thrombin , biophysics , cytoplasm , secretion , platelet , chemistry , calcium , fluorescence , fura 2 , biochemistry , biology , cytosol , physics , immunology , enzyme , organic chemistry , quantum mechanics
Cytoplasmic free [Ca 2+ ], [Ca 2+ ] i , was measured in human platelets using the intracellularly‐trapped, fluorescent indicator quin2. Basal [Ca 2+ ] i with the Ca 2+ ‐ionophore ionomycin revealed apparent thresholds for shape‐change, 5‐HT release and aggregation of approx. 0.5μM, 0.8μM and 2 μM. Thrombin raised [Ca 2+ ] i to 3 μM fast enough for the Ca 2+ to have triggered the cell activation. However, thrombin released more 5‐HT than ionomycin could, and in Ca 2+ ‐free medium thrombin evoked shape‐change and secretion even when [Ca 2+ ] i remained near basal levels throughout, suggesting the existence of alternative triggers for shape‐change and secretory exocytosis.