Modulation of intracellular Ca2+ by glucose in MDCK cells: role of endoplasmic reticulum Ca(2+)-ATPase.
Intracellular free calcium ([Ca2+]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 (pHi) and [Ca2+]i in Madin-Darby canine kidney (MDCK) cells using fluorescent probes, SNARF-1 and fura 2, respectively. The addition of glucose decreased both pHi and [Ca2+]i 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 [Ca2+]i decrease. Without glucose, 1 microM TG induced a sustained elevation in [Ca2+]i, which increased further with glucose addition, whereas 15 microM CPA induced a transient increase in [Ca2+]i that was not affected by further addition of glucose. The sustained elevation in [Ca2+]i induced by TG was dependent on extracellular Ca2+. TG-induced [Ca2+]i increase was modulated by glucose, i.e., at higher glucose concentrations, TG induced a larger and more rapid rise in [Ca2+]i. We conclude that glucose has dual effects on [Ca2+]i regulation. Glucose alone reduces [Ca2+]i by activating ER-type Ca(2+)-ATPase, since this phenomenon is TG and CPA sensitive. In the presence of TG, glucose increases [Ca2+]i probably by increasing Ca2+ entry. Our data suggest a model in which TG activates capacitative Ca2+ entry by depletion of the ER Ca2+ pool. Glucose increases TG-induced [Ca2+]i elevation by further enhancing capacitative Ca2+ entry.
Lien
Y H
YH
Department of Medicine, University of Arizona Health Sciences Center, Tucson 85724, USA.
Wang
X
X
Gillies
R J
RJ
Martinez-Zaguilan
R
R
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000502:physiology*; D002460:Cell Line; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D005110:Extracellular Space / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism*; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008353:Mannitol / Q000494:pharmacology; D009994:Osmolar Concentration; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D013729:Terpenes; D008353:Mannitol; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D005947:Glucose; D002118:Calcium