Z. Wang et al., IMPACT OF CYTOPLASMIC CALCIUM BUFFERING ON THE SPATIAL AND TEMPORAL CHARACTERISTICS OF INTERCELLULAR CALCIUM SIGNALS IN ASTROCYTES, The Journal of neuroscience, 17(19), 1997, pp. 7359-7371
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.