Figure 3. Dependence of 5-[³H]HT binding on Na⁺ and Cl⁻.

A, sodium dependence of 5-[³H]HT binding. Levels of specific binding (‘B’) were measured at both 0.1 and 0.5 μm of ³H-ligand, and with varying [Na⁺]_o (by isotonic substitution with Li⁺) and constant [Cl⁻]_o of 137.4 mm. Analogous substitutions with K⁺, Cs⁺, Rb⁺ or choline all led to comparable findings to substitutions with Li⁺. B, chloride dependence of 5-[³H]HT binding. Specific binding levels (‘B’) were measured at both 0.1 and 0.5 μm 5-[³H]HT with varying [Cl⁻]_o (by isotonic substitution with isethionate ion) and constant [Na⁺]_o of 128 mm. Analogous substitutions by F⁻, Br⁻ or I⁻ also led to comparable findings. Non-specific binding levels were assessed by inclusion of 100 μm imipramine. Each point is the mean ±s.d. of six values.