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The sodium‐calcium exchanger is a mechanosensitive transporter
Author(s) -
Reeves John P.,
Abdellatif Maha,
Condrescu Madalina
Publication year - 2008
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 - 10.1113/jphysiol.2008.151274
Subject(s) - chemistry , tonicity , biophysics , extracellular , calcium , sodium , sodium calcium exchanger , osmotic concentration , cytosol , efflux , intracellular , biochemistry , biology , enzyme , organic chemistry
This report describes the influence of fluid flow and osmotically induced volume changes on Na + –Ca 2+ exchange (NCX) activity in transfected CHO cells. Exchange activity was measured as Na + ‐dependent Ca 2+ or Ba 2+ fluxes using the fluorescent probe fura‐2. When exchange activity was initiated by superfusing Ba 2+ ‐containing solutions over the cells for a 20 s interval, a high rate of Ba 2+ uptake was observed while the solution was being applied but the rate of Ba 2+ uptake declined > 10‐fold when the solution flow ceased. Ba 2+ efflux in exchange for extracellular Na + or Ca 2+ (Ba 2+ –Ca 2+ exchange) was similarly biphasic. During NCX‐mediated Ca 2+ uptake, a rapid increase in cytosolic [Ca 2+ ] to a peak value occurred, followed by a decline in [Ca 2+ ] i to a lower steady‐state value after solution flow ceased. When NCX activity was initiated by an alternate procedure that minimized the duration of solution flow, the rapid phase of Ba 2+ influx was greatly reduced in magnitude and Ca 2+ uptake became nearly monophasic. Solution superfusion did not produce any obvious changes in cell shape or volume. NCX‐mediated Ba 2+ and Ca 2+ influx were also sensitive to osmotically induced changes in cell volume. NCX activity was stimulated in hypotonic media and inhibited in hypertonic media; the osmotically induced changes in activity occurred within seconds and were rapidly reversible. We conclude that NCX activity is modulated by both solution flow and osmotically induced volume changes.