Figure 7. Intracellular Ca²⁺ is required also for activation of I_mtx.

A, control experiment showing the activation of I_mtx in response to 500 pm MTX with [Ca²⁺]_o = 2 mm and [Ca²⁺]_i = 1 μm. B, activation of I_mtx when [Ca²⁺]_o = 2 mm and [Ca²⁺]_i is near zero with 5 mm BAPTA in the pipette solution. The voltage ramp used here is the same as in Fig. 3A. C, mean ± s.d. from experiments with or without BAPTA in the pipette solution. In BAPTA loaded cells only 4.57 % of the current obtained in control conditions was observed (n = 5). The values of the I_mtx current were obtained by subtracting the basal fibroblast K⁺ current (I₁, ▾) from the total current activated by MTX (I₂, ▿, n = 10). The graph shows the values of the current corrected by capacitance (I₂ – I₁/C). The capacitance of the cells varied between 8 and 12 pF.