Filling state of intracellular Ca2+ pools triggers trans plasma membrane Na+ and Ca2+ influx by a tyrosine kinase-dependent pathway.
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.
Tepel
M
M
Medizinische Universitäts-Poliklinik, University of Münster, Federal Republic of Germany.
Kühnapfel
S
S
Theilmeier
G
G
Teupe
C
C
Schlotmann
R
R
Zidek
W
W
D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D008214:Lymphocytes / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D012964:Sodium / Q000378:metabolism*; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D013729:Terpenes; D019284:Thapsigargin; D012964:Sodium; D011505:Protein-Tyrosine Kinases; D000252:Calcium-Transporting ATPases; D002118:Calcium