FIGURE 10.

(a) The R-values of COS-7 cells expressing Clomeleon clamped to 0 mM, 30 mM, and 50 mM chloride concentrations. The R-values decreased with increasing chloride concentrations from 1.59 ± 0.18 (0 mM) to 0.58 ± 0.07 (50 mM). (b) Comparison of R-values from COS-7 cells yielded the intracellular chloride concentrations in hippocampal neurons at different stages of maturation. A drastic decrease in the chloride concentrations was found for all the classes along neuronal development. The minimum chloride concentration was observed for class III (light shading) at DIV 15 and the maximum for class I (solid) at DIV 7. (c) A sigmoidal decrease in the intracellular chloride concentrations of neurons with increasing maturation was observed on comparing the individual R-values with the number of primary processes they possess. (d) The ratios of acceptor-to-donor mean lifetimes of Clomeleon in solution at varying chloride concentrations. A comparison of these ratios from solutions with those obtained from the different fractions of mature neurons allowed the determination of intracellular chloride concentrations of the latter, similar to those obtained from R-values of COS-7 cells.