Figure 1. The threshold voltage of depolarization for the depolarization-activated Ca²⁺ entry in uterine myocytes.

A, traces show (from top to bottom): membrane potential (V_m), [Ca²⁺]_i and membrane current (I_Ca). The inset shows the current records on an expanded time scale. B, steady-state inactivation (•) and activation (○) of I_Ca as a function of membrane potential. The continuous lines were obtained by fitting Boltzmann equations to the experimental data. Half-inactivation occurred at -53 mV with a slope factor of 9.9 mV. The potential for half-activation was -27 mV, with a slope factor of 11 mV. Error bars are s.e.m. (n = 6).