Modulation of intracellular Ca2+ by glucose in MDCK cells: role of endoplasmic reticulum Ca (2+) -ATPase
Lien, Y.H.; Wang, X.; Gillies, R.J.; Martinez-Zaguilan, R.
American Journal of Physiology 268(4 Pt 2): F671-F679
1995
ISSN/ISBN: 0002-9513 PMID: 7733324 Document Number: 440140
Intracellular free calcium ((Ca-2+)-i) has multiple functional roles in renal epithelia, including mediating ligand- and volume-activated K+ and Cl- channels, modulating the permeability of apical membrane to Na+, and regulating tubuloglomerular feedback. We investigated glucose effects on intracellular pH (pH-i) and (Ca-2+), in Madin-Darby canine kidney (MDCK) cells using fluorescent probes, SNARF-1 and fura 2, respectively. The addition of glucose decreased both pH-i and (Ca-2+), in a dose-dependent fashion. Thapsigargin (TG) and cyclopiazonic acid (CPA), well-known endoplasmic reticulum (ER) Ca-2+-adenosinetriphosphatase (Ca-2+-ATPase) inhibitors, abolished the glucose-induced (Ca-2+)-i decrease. Without glucose, 1 mu-M TG induced a sustained elevation in (Ca-2+)-i, which increased further with glucose addition, whereas 15 mu-M CPA induced a transient increase in (Ca-2+), that was not affected by further addition of glucose. The sustained elevation in (Ca-2+), induced by TG was dependent on extracellular Ca-2+. TG-induced (Ca-2+), increase was modulated by glucose, i.e., at higher glucose concentrations, TG induced a larger and more rapid rise in (Ca-2+)-i. We conclude that glucose has dual effects on (Ca-2+)-i regulation. Glucose alone reduces (Ca-2+)-i by activating ER-type Ca-2+ATPase, since this phenomenon is TG and CPA sensitive. In the presence of TG, glucose increases (Ca-2+)-i, probably by increasing Ca-2+ entry. Our data suggest a model in which TG activates capacitative Ca-2+ entry by depletion of the ER Ca-2+ pool. Glucose increases TG-induced (Ca-2+)-i elevation by further enhancing capacitative Ca-2+ entry.