The sodium-calcium exchanger is a mechanosensitive transporter.
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.
Reeves
John P
JP
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
Abdellatif
Maha
M
Condrescu
Madalina
M
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*
D019831:Sodium-Calcium Exchanger