IMPACT OF CYTOPLASMIC CALCIUM BUFFERING ON THE SPATIAL AND TEMPORAL CHARACTERISTICS OF INTERCELLULAR CALCIUM SIGNALS IN ASTROCYTES

The impact of calcium buffering on the initiation and propagation of m echanically elicited intercellular Ca2+ waves was studied using astroc ytes loaded with different exogenous, cell membrane-permeant Ca2+ chel ators and a laser scanning confocal or video fluorescence microscope. Using an ELISA with a novel antibody to BAPTA, we showed that differen t cell-permeant chelators, when applied at the same concentrations, ac cumulate to the same degree inside the cells, Loading cultures with BA PTA, a high Ca2+ affinity chelator, almost completely blocked calcium wave occurrence. Chelators having lower Ca2+ affinities had lesser aff ects, as shown in their attenuation of both the radius of spread and p ropagation velocity of the Ca2+ wave. The chelators blocked the proces s of wave propagation, not initiation, because large [Ca2+](i) increas es elicited in the mechanically stimulated cell were insufficient to t rigger the wave in the presence of high Ca2+ affinity buffers. Wave at tenuation was a function of cytoplasmic Ca2+ buffering capacity; i.e., loading increasing concentrations of low Ca2+ affinity buffers mimick ed the effects of lesser quantities of high affinity chelators. In che lator-treated astrocytes, changes in calcium wave properties were inde pendent of the Ca2+-binding rate constants of the chelators, of chelat ion of other ions such as Zn2+, and of effects on gap junction functio n, Slowing of the wave could be completely accounted for by the slowin g of Ca2+ ion diffusion within the cytoplasm of individual astrocytes. The data obtained suggest that alterations in Ca2+ buffering may prov ide a potent mechanism by which the localized spread of astrocytic Ca2 + signals is controlled.