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Voltage‐dependent Ca 2+ release in rat megakaryocytes requires functional IP 3 receptors
Author(s) -
Mason Michael J.,
MahautSmith Martyn P.
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.0175b.x
Subject(s) - depolarization , thapsigargin , biophysics , receptor , inositol , chemistry , agonist , stimulation , inositol trisphosphate , intracellular , endocrinology , medicine , biology , biochemistry
Using simultaneous whole‐cell patch‐clamp and fluorescence measurements of [Ca 2+ ] i in rat megakaryocytes we have investigated the requirement for functional inositol 1,4,5‐trisphosphate (IP 3 ) receptors in Ca 2+ release induced by membrane depolarization during agonist stimulation. Voltage‐dependent Ca 2+ release was observed during application of the IP 3 ‐generating agonists U46619 (a thromboxane A 2 analogue) and ADP. Furthermore, voltage‐dependent Ca 2+ release was observed in the absence of exogenous agonist following sensitization of IP 3 receptors with thimerosal. Depolarization‐induced Ca 2+ release was not detected during depletion of intracellular Ca 2+ stores by thapsigargin. Thus, depletion of stores alone is not sufficient to confer voltage dependence upon the Ca 2+ release mechanism. Block of IP 3 receptors by carbacyclin‐stimulated elevations in cAMP, uncaging of cAMP or exposure to a high concentration of caffeine reversibly abolished Ca 2+ increases stimulated by both ADP and depolarization. The cAMP‐dependent block was prevented by a peptide inhibitor of protein kinase A, indicating that an alteration of adenylate cyclase activity leading to modulation of protein kinase A activity does not underlie the control of Ca 2+ release by voltage. These results are consistent with the requirement for functional IP 3 receptors for voltage control of Ca 2+ release from intracellular stores during inositol lipid signalling. The data also indicate the involvement of a voltage sensor downstream of surface membrane receptors in the depolarization‐evoked Ca 2+ response.