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  • Title: Filling state of intracellular Ca2+ pools triggers trans plasma membrane Na+ and Ca2+ influx by a tyrosine kinase-dependent pathway.
    Author: Tepel M, Kühnapfel S, Theilmeier G, Teupe C, Schlotmann R, Zidek W.
    Journal: J Biol Chem; 1994 Oct 21; 269(42):26239-42. PubMed ID: 7929340.
    Abstract:
    The relations between the filling state of intracellular calcium stores that are regulated by the endoplasmic Ca(2+)-ATPase and trans plasma membrane sodium and calcium influx were investigated. The effects of specific inhibition of endoplasmic Ca(2+)-ATPase by thapsigargin, cyclopiazonic acid, and 2,5-di-(tert-butyl)-1,4-benzohydroquinone (BHQ) on cytosolic free sodium concentration ([Na+]i) and cytosolic free calcium concentration ([Ca2+]i) were evaluated in lymphocytes from healthy subjects using the fluorescent dyes sodium-binding benzofuran isophthalate and fura2. The specific inhibition of endoplasmic Ca(2+)-ATPase by thapsigargin, cyclopiazonic acid, or BHQ increased lymphocytic [Na+]i and [Ca2+]i. The thapsigargin-induced [Na+]i increase was abolished in the absence of external sodium, indicating that thapsigargin induced a trans plasma membrane sodium influx. In the absence of external calcium the thapsigargin-induced [Ca2+]i increase was significantly reduced, whereas the thapsigargin-induced [Na+]i increase remained the same. This finding indicates that the filling state of intracellular calcium pools rather than the elevation of [Ca2+]i per se regulates the plasma membrane permeability for sodium in lymphocytes. The inhibition of the tyrosine kinase by genistein inhibited the thapsigargin-induced increases of both [Na+]i and [Ca2+]i in lymphocytes. The present study shows that the filling state of intracellular thapsigargin-sensitive calcium pools regulates trans plasma membrane sodium and calcium influx via a tyrosine kinase-dependent pathway.
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