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ADP and inositol trisphosphate evoke oscillations of a monovalent cation conductance in rat megakaryocytes
Author(s) -
Hussain Jamila F.,
MahautSmith Martyn P.
Publication year - 1998
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.1469-7793.1998.791bg.x
Subject(s) - divalent , chemistry , conductance , biophysics , intracellular , inositol , bapta , reversal potential , patch clamp , analytical chemistry (journal) , biochemistry , chromatography , receptor , biology , mathematics , organic chemistry , combinatorics
1 A combination of conventional whole‐cell patch clamp recordings and fura‐2 fluorescence photometry was used to study the membrane currents during oscillations of intracellular Ca 2+ concentration ([Ca 2+ ] i ) in single rat megakaryocytes. 2 At a holding potential of ‐60 mV, in NaCl external saline and KCl internal saline with low levels of Ca 2+ buffering, 10 μ m ADP evoked [Ca 2+ ] i oscillations and simultaneous Ca 2+ ‐gated K + currents at a frequency of 3–10 spikes min −1 . A smaller inward current was also activated, with a time course that identified this component as the inositol 1,4,5‐trisphosphate (IP 3 )‐activated monovalent cation current previously demonstrated in rat megakaryocytes. 3 Cs + replacement of internal K + combined with 100 nM external charybdotoxin (CTX) abolished the outward currents and revealed that an inward current was also transiently activated during each [Ca 2+ ] i spike. This underlying conductance was permeable to Na + and Cs + , but possessed little or no permeability to Cl − or divalent cations. 4 Intracellular dialysis with IP 3 (5‐50 μ m ) activated the monovalent cationic conductance prior to release of Ca 2+ from intracellular stores. The [Ca 2+ ] i increase was associated with a second phase of cationic current, implying that both IP 3 and Ca 2+ can activate this conductance. Buffering of [Ca 2+ ] i with BAPTA abolished the second phase of current, leaving monophasic spikes of inward current, often occurring at regular intervals. 5 These data demonstrate that a monovalent cation current, which results in Na + influx under normal ionic conditions, oscillates in response to ADP receptor stimulation due to activation by both IP 3 and [Ca 2+ ] i . This provides a route for long‐term Na + entry in the megakaryocyte following stimulation of receptors coupled to phospholipase C activation and may play a role in cell shape change.