Spontaneous and beta-adrenergic receptor-mediated taurine release from astroglial cells are independent of manipulations of intracellular calcium.
Stimulation of beta-adrenergic receptors on LRM55 astroglial cells results in cAMP-dependent release of taurine. We have previously demonstrated that extracellular Ca2+ is not required for either spontaneous or receptor-mediated taurine release (Martin et al., 1988b). In the present series of experiments we investigated the relationship between changes in intracellular free Ca2+ ([Ca2+]i) and taurine release. [Ca2+]i was measured using the fluorescent probe fura-2 and was manipulated by changing the concentration of Ca2+ in the incubation medium and by using the Ca2+ ionophore ionomycin. [Ca2+]i was reduced from 150 +/- 95 nM (n = 46) in control medium (containing 1.1 mM CaCl2) to 46 +/- 10 nM (n = 43) in saline containing no CaCl2 and 10 microM EGTA. [Ca2+]i was rapidly elevated to greater than or equal to 1 microM in medium containing 100 microM CaCl2 and 10 microM ionomycin. Taurine release, either spontaneous or stimulated by isoproterenol, was not significantly affected by these manipulations of [Ca2+]i. [Ca2+]i did not change when cells were stimulated with 100 nM isoproterenol in either control saline containing 1.1 mM CaCl2 or in CaCl2-free saline containing 10 microM EGTA. Other secretogogs (serotonin and ethanol) did not cause changes in [Ca2+]i. These data indicate that neither spontaneous or receptor-mediated taurine release from astroglial cells is Ca2+ dependent. However, when cells were preloaded with Ca2+, allowed to recover briefly, and then stimulated with isoproterenol, it was possible to demonstrate transient increases in Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)
Shain
W
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Laboratory of Neurotoxicology and Nervous System Disorders, Wadsworth Center for Laboratories and Research, Albany, New York 12201.
Connor
J A
JA
Madelian
V
V
Martin
D L
DL
D001253:Astrocytes / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002478:Cells, Cultured; D004987:Ethers / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism*; D015759:Ionomycin; D007476:Ionophores; D009994:Osmolar Concentration; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D013654:Taurine / Q000378:metabolism*
D004987:Ethers; D007476:Ionophores; D011943:Receptors, Adrenergic, beta; D013654:Taurine; D015759:Ionomycin; D002118:Calcium