FIGURE 7.

Ca²⁺-concentration dependence of the pH jump induced fluorescence relaxation. Experiments as shown in Fig. 5 were performed in the presence of various Ca²⁺ concentrations. The time course of the fluorescence signal was fitted with the sum of two exponentials (Eq. 1). The time constants, τ_i, and the fluorescence amplitudes, F_i, were plotted against the concentration of free Ca²⁺ in the electrolyte. (A) The time constant of the fast process, τ₁ = 8.3 ms, was Ca²⁺-concentration independent whereas the slower process was decelerated at Ca²⁺ concentrations above 1 μM. (B) The amplitude of both components of the fluorescence signal decreased at concentrations >5 μM. Above 400 μM Ca²⁺ no significant fluorescence changes could be detected.