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Osmotic Swelling‐Induced Changes in Cytosolic Calcium Do Not Affect Regulatory Volume Decrease in Rat Cultured Suspended Cerebellar Astrocytes
Author(s) -
MoralesMulia Sandra,
Vaca Luis,
HernandezCruz Arturo,
PasantesMorales Herminia
Publication year - 1998
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1998.71062330.x
Subject(s) - ionomycin , ryanodine receptor , thapsigargin , medicine , bapta , endocrinology , calcium , fura 2 , intracellular , endoplasmic reticulum , chemistry , biophysics , cytosol , extracellular , calcium in biology , biology , biochemistry , enzyme
Hyposmotic swelling‐induced changes in intracellular Ca 2+ concentration ([Ca 2+ ] 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 [Ca 2+ ] i from 117 n M to a mean peak increase of 386 (50%) and 220 n M (30%), followed by a maintained plateau phase. Ca 2+ influx through the plasmalemma as well as release from internal stores contributed to this osmosensitive [Ca 2+ ] i elevation. Omission of external Ca 2+ or addition of Cd 2+ , Mn 2+ , or Gd 3+ did not reduce RVD, although it was decreased by La 3+ (0.1–1 m M ). Verapamil did not affect either the swelling‐evoked [Ca 2+ ] i or RVD. Maneuvers that deplete endoplasmic reticulum (ER) Ca 2+ stores, such as treatment (in Ca 2+ ‐free medium) with 0.2 µ M thapsigargin (Tg), 10 µ M 2,5‐di‐ tert ‐butylhydroquinone, 1 µ M ionomycin, or 100 µ M ATP abolished the increase in [Ca 2+ ] i but did not affect RVD. However, prolonged exposure to 1 µ M Tg blocked RVD regardless of ER Ca 2+ content or cytosolic Ca 2+ levels. Ryanodine (up to 100 µ M ) and caffeine (10 m M ) did not modify [Ca 2+ ] i or RVD. BAPTA‐acetoxymethyl ester (20 µ M ) abolished [Ca 2+ ] i elevation without affecting RVD, but at higher concentrations BAPTA prevented cell swelling and blocked RVD. We conclude that the osmosensitive [Ca 2+ ] i rise occurs as a consequence of increased Ca 2+ permeability of plasma and organelle membranes, but it appears not relevant as a transduction signal for RVD in rat cultured cerebellar astrocytes.