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A novel role for membrane potential in the modulation of intracellular Ca 2+ oscillations in rat megakaryocytes
Author(s) -
Mason Michael J.,
Hussain Jamila F.,
MahautSmith Martyn P.
Publication year - 2000
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.1469-7793.2000.00437.x
Subject(s) - biophysics , depolarization , membrane potential , intracellular , extracellular , afterdepolarization , current clamp , voltage clamp , oscillation (cell signaling) , chemistry , electrophysiology , reversal potential , physics , patch clamp , repolarization , neuroscience , biology , biochemistry
1 The effect of membrane potential ( V m ) on ADP‐evoked [Ca 2+ ] i oscillations was investigated in rat megakaryocytes, a non‐excitable cell type recently shown to exhibit depolarisation‐evoked Ca 2+ release from intracellular stores during metabotropic purinoceptor stimulation. 2 Hyperpolarising voltage steps caused a transient fall in [Ca 2+ ] i and either abolished Ca 2+ oscillations or reduced the oscillation amplitude. These effects were observed in both the presence and absence of extracellular Ca 2+ and also in Na + ‐free saline solutions, suggesting that hyperpolarisation leads to a reduction in the level of ADP‐dependent Ca 2+ release without a requirement for altered transmembrane Ca 2+ fluxes. 3 In the presence of Ca 2+ oscillations, depolarising voltage steps transiently enhanced the amplitude of Ca 2+ oscillations. Following run‐down of Ca 2+ oscillations, depolarisation briefly restimulated oscillations. 4 Simultaneous [Ca 2+ ] i and current‐clamp recordings showed that Ca 2+ and V m oscillate in synchrony, with an average fluctuation of approximately 30–40 mV, due to activation and inactivation of Ca 2+ ‐dependent K + channels. Application of a physiological oscillating V m waveform to non‐oscillating cells under voltage clamp stimulated [Ca 2+ ] i oscillations. 5 Analysis of the relationship between [Ca 2+ ] i and V m showed a threshold for activation of hyperpolarisation at about 250–300 nM. The implications of this threshold in the interaction between V m and Ca 2+ release during oscillations are discussed. 6 We conclude that the ability of voltage to control release of endosomal Ca 2+ in ADP‐stimulated megakaryocytes is bipolar in nature. Our data suggest that V m changes are active components of the feedback/feedforward mechanisms contributing to the generation of Ca 2+ oscillations.