The rate of diffusion of Ca2+ and Ba2+ in a nerve cell body.

A spectrophotometric method was developed to directly measure the diffusion rate of Ca2+ and some other ions in nerve cell bodies, using pulsed ionophoretic injections and an optical microprobe to record locally absorbance changes of the dye arsenazo III. We report here that Ca2+ and Ba2+ diffuse at approximately the same rate in nerve soma cytoplasm, having effective diffusion coefficients in the range of 7-12 X 10(-7) cm2/s, while identical measurements conducted in an electrolytic solution yielded values of 5.2 X 10(-6) cm2/s for Ca and 5.4 X 10(-6) cm2/s for Ba. The results are discussed in relation to the mechanisms that regulate the intracellular concentration of free Ca.