Fig. 1. I_CRAC is smaller using hyperpolarizing steps than ramps in weak intracellular Ca²⁺ buffer. (A) Time-course of I_CRAC, followed using voltage ramps, in strong and weak buffer (filled and open circles, respectively). Inset shows I–V relationships taken at 100 s. The current was measured at –80 mV from the ramps, and normalized for cell capacitance. (B) Time-course of I_CRAC in strong and weak buffer following voltage steps to –80 mV (inset). The current was measured between 0.8 and 0.9 ms after the step (see Materials and methods). (C) A plot of I_CRAC against activation time-constant in strong buffer using ramps or steps. (D) A similar plot to (C) but for low buffer. Note that inclusion of 2 mM Mg-ATP reduces the size of the current.