Stimulation of calcium uptake in cultured astrocytes by hypoosmotic stress--effect of cyclic AMP.
To investigate the role of Ca2+ in astrocyte volume regulation, we determined Ca2+ fluxes following hypoosmotic stress and how these fluxes were modified by cyclic AMP. In isoosmotic conditions treatment with dibutyryl cyclic AMP (dBcAMP) caused almost a twofold increase in 45Ca2+ uptake. Efflux studies of 45Ca2+ in dBcAMP-treated cells showed three Ca2+ compartments while only two Ca2+ compartments were identified in non-dBcAMP-treated cells. Following hypoosmotic stress a twofold stimulation of 45Ca2+ uptake occurred in both non-dBcAMP-treated and dBcAMP-treated astrocytes. Stimulation of Ca2+ uptake begins at approximately 270 mOsm and is half-maximally stimulated at approximately 100 mOsm. This uptake is partly mediated through L-type 'slow' inactivating Ca2+ channels. Hypoosmotic stress also induces the release of Ca2+ from intracellular stores. The influx of extracellular Ca2+ and efflux of intracellular Ca2+ appear to be important factors in volume regulation after hypoosmotic stress. Cyclic AMP plays an important role in modulating hypoosmotically stimulated Ca2+ uptake.
Bender
A S
AS
Department of Pathology, University of Miami School of Medicine, FL 33101.
Mantelle
L L
LL
Norenberg
M D
MD
D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000502:physiology; D009994:Osmolar Concentration; D009995:Osmosis; D011493:Protein Kinase C / Q000502:physiology; D051381:Rats; D013312:Stress, Physiological / Q000378:metabolism*; D013997:Time Factors
D002121:Calcium Channel Blockers; D003994:Bucladesine; D000242:Cyclic AMP; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D002118:Calcium