FIG. 7.

Effect of increasing extracellular Ca²⁺ on NcTOKA currents. SBS containing 10 mM KCl and various concentrations of CaCl₂ was used. The holding potential was −76 mV, and voltage pulses ranged from +44 to −156 mV in 10-mV steps. (A and B) The extracellular Ca²⁺ concentration was varied between 0.1 and 40 mM, but only currents in 1 (A) and 10 (B) mM are shown. (C) Current-voltage relationship of NcTOKA currents with various extracellular Ca²⁺ activities. (Inset) Inhibition of currents at +44 mV plotted as a function of extracellular Ca²⁺ activity. Data were fitted with equation 2: I_obs = I_max − [(I_min [Ca])/(K_i + Ca)] where I_max is current in the absence of Ca²⁺ (961 pA), I_min is the current at saturating Ca²⁺ (78 pA), [Ca] is the extracellular Ca²⁺ activity, and K_i is the inhibition constant for Ca²⁺ (activity of 2.8 mM).