Figure 3.

Relative effects of Ca²⁺ and H⁺ in enhancing P_o at negative voltages. A. Representative openings at −120 mV at pH_i = 7.5 without Ca²⁺ (top), pH_i = 7.5 with 200 μM Ca²⁺ (middle) and pH_i = 6.2 without Ca²⁺ (bottom) in the Ca²⁺ bowl-defective Slo1 mutant channel (Δ854-846). The patch contained ~85 channels. Sixty 1-s data segments are shown superimposed. The closed level is indicated by “c”. B. Relative P_o with 200 μM Ca²⁺ at pH_i =7.5 (left) and pH_i = 6.2 without Ca²⁺ (right) compared with P_o at pH_i =7.5 without Ca²⁺ in the Slo1 Δ854-846 channel. P_o in each condition was normalized to that measured at pH_i = 7.5 without Ca²⁺ in each patch. C. Estimated value of the HA model parameter C for Ca²⁺ (200 μM) and H⁺ (pH_i = 6.2) using the results obtained at −120 mV in the Slo1 Δ854-846 channel. The P_o ratio values were raised to the ¼th power to estimate C. The top diagram shows a subset of the HA model at negative voltages without any ligand and the bottom diagram shows the same subset with saturating Ca²⁺ or H⁺. D. Relative P_o at pH_i = 6.2 without Ca²⁺ compared with P_o at pH_i =7.5 without Ca²⁺ in the H365R:H394R channel (open circles) and the H365A:H394A channel (filled triangles).