Osmotic swelling-induced changes in cytosolic calcium do not affect regulatory volume decrease in rat cultured suspended cerebellar astrocytes.
Hyposmotic swelling-induced changes in intracellular Ca2+ concentration ([Ca2+]i) and their influence on regulatory volume decrease (RVD) were examined in rat cultured suspended cerebellar astrocytes. Hyposmotic media (50 or 30%) evoked an immediate rise in [Ca2+]i from 117 nM to a mean peak increase of 386 (50%) and 220 nM (30%), followed by a maintained plateau phase. Ca2+ influx through the plasmalemma as well as release from internal stores contributed to this osmosensitive [Ca2+]i elevation. Omission of external Ca2+ or addition of Cd2+, Mn2+, or Gd3+ did not reduce RVD, although it was decreased by La3+ (0.1-1 mM). Verapamil did not affect either the swelling-evoked [Ca2+]i or RVD. Maneuvers that deplete endoplasmic reticulum (ER) Ca2+ stores, such as treatment (in Ca2+-free medium) with 0.2 microM thapsigargin (Tg), 10 microM 2,5-di-tert-butylhydroquinone, 1 microM ionomycin, or 100 microM ATP abolished the increase in [Ca2+]i but did not affect RVD. However, prolonged exposure to 1 microM Tg blocked RVD regardless of ER Ca2+ content or cytosolic Ca2+ levels. Ryanodine (up to 100 microM) and caffeine (10 mM) did not modify [Ca2+]i or RVD. BAPTA-acetoxymethyl ester (20 microM) abolished [Ca2+]i elevation without affecting RVD, but at higher concentrations BAPTA prevented cell swelling and blocked RVD. We conclude that the osmosensitive [Ca2+]i rise occurs as a consequence of increased Ca2+ permeability of plasma and organelle membranes, but it appears not relevant as a transduction signal for RVD in rat cultured cerebellar astrocytes.
Morales-Mulia
S
S
Department of Biophysics, Institute of Cell Physiology, National University of Mexico, Mexico City.
Vaca
L
L
Hernandez-Cruz
A
A
Pasantes-Morales
H
H
D000818:Animals; D001253:Astrocytes / Q000166:cytology* / Q000378:metabolism* / Q000502:physiology*; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D009994:Osmolar Concentration; D009995:Osmosis / Q000502:physiology*; D051381:Rats; D012996:Solutions / Q000737:chemistry / Q000494:pharmacology
D012996:Solutions; D002118:Calcium