title: The sodium-calcium exchanger is a mechanosensitive transporter.
abstract: 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.
authors.affiliation: Department of Pharmacology & Physiology, University of Medicine and Dentistry of New Jersey, Graduate School of Biomedical Sciences, 185 South Orange Avenue, Newark, NJ 07101-1709, USA. reeves@umdnj.edu
authors.forename: John P
authors.initials: JP
authors.lastname: Reeves
authors.forename: Maha
authors.initials: M
authors.lastname: Abdellatif
authors.forename: Madalina
authors.initials: M
authors.lastname: Condrescu
mesh_terms: D000818:Animals; D016466:CHO Cells; D048429:Cell Size; D006224:Cricetinae; D003412:Cricetulus; D006801:Humans; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D014882:Water-Electrolyte Balance / Q000502:physiology*
chemical_list: D019831:Sodium-Calcium Exchanger