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Calcium permeability and flux through osmosensory transduction channels of isolated rat supraoptic nucleus neurons
Author(s) -
Zhang Zizhen,
Bourque Charles W.
Publication year - 2006
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/j.1460-9568.2006.04670.x
Subject(s) - supraoptic nucleus , biophysics , chemistry , calcium , nucleus , tonicity , medicine , endocrinology , biochemistry , microbiology and biotechnology , biology , organic chemistry
Hypertonic stimuli delivered into the supraoptic nucleus provoke neuropeptide release from the somata of magnocellular neurosecretory cells (MNCs) in the presence of tetrodotoxin, suggesting that such stimuli can increase intracellular calcium concentration ([Ca 2+ ] i ) in the absence of action potentials. We therefore examined whether the stretch‐inhibited cation (SIC) channels of MNCs can mediate calcium influx. Whole‐cell recordings were made in MNCs isolated from the supraoptic nuclei of adult rats. Measurements of reversal potentials in different solutions revealed that the current induced by a suction‐evoked decrease in cell volume ( I SIC ) displays a selectivity sequence for monovalent cations of K + > Cs + > Na + > NMDG + . The permeability of SIC channels to Ca 2+ , relative to Na + , was ∼ 5. In the presence of physiological concentrations of external Na + and K + , the amplitude of inward I SIC was reduced dose‐dependently by external Ca 2+ with an IC 50 of 4.9 m m . This was not due to reduced suction‐evoked volume changes or to an accumulation of [Ca 2+ ] i . Confocal imaging of cytoplasmic Calcium Green‐1 fluorescence revealed that activation of I SIC significantly increases [Ca 2+ ] i in physiological solutions. This effect is absent in Ca 2+ ‐free solution, or when Gd 3+ (300 µ m ) is added to Ca 2+ ‐containing solution. Part of this effect is inhibited in the presence of dantrolene (10 µ m ) and heparin (4 mg/mL), suggesting that release from intracellular Ca 2+ stores participates in suction‐evoked Ca 2+ signalling. These observations indicate that SIC channels are highly permeable to Ca 2+ , mediate significant Ca 2+ entry and release of Ca 2+ from internal stores under conditions when the volume of MNCs is decreased.