Calcium entry into cultured mouse astrocytes.
The barium-sensitive component of transmembrane influx of 45Ca into cultured mouse astrocytes was investigated in order to find clues for an involvement of a glial Ca2+ uptake system in Ca2+ movements of the CNS. The Ca2+ turnover was very high amounting to a rate constant of 1.4 min-1. The magnitude of the Ca2+ flux was, however, only about 2% of the K+ flux. It had the same magnitude as the Cl- flux. The Ca2+ influx was not sensitive to the organic Ca2+ channel blockers verapamil and nifedipine; however, cadmium, cobalt and barium blocked the flux in millimolar concentrations. The Ca2+ influx was a linear function of the external Ca2+ concentration up to 1.8 mM. A further increase in external Ca2+ did not increase the magnitude of the influx. Increases in external K+ to the physiological ceiling level of 12 mM (which corresponds to a 15 mV depolarization) and to 54 mM (48 mV depolarization) had no effect on the system. We conclude that the Ca2+ entry system of glial cells is not involved in the decrease of the external Ca2+ concentration during neuronal activity. The barium-evoked spontaneous depolarizations of astrocytes reported in the literature are probably due to the blockade of K+ channels by barium, since 50 microM barium did not affect the Ca2+ flux and increased the total Ca2+:K+ flux ratio from 1:50 to 1:2.5.
D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002463:Cell Membrane Permeability / Q000187:drug effects; D002478:Cells, Cultured; D002540:Cerebral Cortex; D007473:Ion Channels / Q000502:physiology; D051379:Mice; D011188:Potassium / Q000378:metabolism
D002121:Calcium Channel Blockers; D007473:Ion Channels; D011188:Potassium; D002118:Calcium