title: Impact of cytoplasmic calcium buffering on the spatial and temporal characteristics of intercellular calcium signals in astrocytes.
abstract: The impact of calcium buffering on the initiation and propagation of mechanically elicited intercellular Ca2+ waves was studied using astrocytes loaded with different exogenous, cell membrane-permeant Ca2+ chelators and a laser scanning confocal or video fluorescence microscope. Using an ELISA with a novel antibody to BAPTA, we showed that different cell-permeant chelators, when applied at the same concentrations, accumulate to the same degree inside the cells. Loading cultures with BAPTA, a high Ca2+ affinity chelator, almost completely blocked calcium wave occurrence. Chelators having lower Ca2+ affinities had lesser affects, as shown in their attenuation of both the radius of spread and propagation velocity of the Ca2+ wave. The chelators blocked the process of wave propagation, not initiation, because large [Ca2+]i increases elicited in the mechanically stimulated cell were insufficient to trigger the wave in the presence of high Ca2+ affinity buffers. Wave attenuation was a function of cytoplasmic Ca2+ buffering capacity; i.e., loading increasing concentrations of low Ca2+ affinity buffers mimicked the effects of lesser quantities of high-affinity chelators. In chelator-treated astrocytes, changes in calcium wave properties were independent of the Ca2+-binding rate constants of the chelators, of chelation of other ions such as Zn2+, and of effects on gap junction function. Slowing of the wave could be completely accounted for by the slowing of Ca2+ ion diffusion within the cytoplasm of individual astrocytes. The data obtained suggest that alterations in Ca2+ buffering may provide a potent mechanism by which the localized spread of astrocytic Ca2+ signals is controlled.
authors.affiliation: Departments of Cell Biology and Anatomy and Neurosurgery, New York Medical College, Valhalla, New York 10595, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Wang
authors.forename: M
authors.initials: M
authors.lastname: Tymianski
authors.forename: O T
authors.initials: OT
authors.lastname: Jones
authors.forename: M
authors.initials: M
authors.lastname: Nedergaard
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000502:physiology*; D002021:Buffers; D002118:Calcium / Q000378:metabolism* / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000493:pharmacokinetics; D005456:Fluorescent Dyes; D017629:Gap Junctions / Q000502:physiology; D007202:Indicators and Reagents / Q000493:pharmacokinetics; D007425:Intracellular Membranes / Q000378:metabolism*; D009994:Osmolar Concentration; D051381:Rats / Q000196:embryology; D015398:Signal Transduction; D013997:Time Factors; D014018:Tissue Distribution
chemical_list: D002021:Buffers; D002614:Chelating Agents; D005456:Fluorescent Dyes; D007202:Indicators and Reagents; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium