Fig. 9.

Activation and inactivation plots of the L-type Ca²⁺ channel from sham-operated (Sham), ovariectomized (OVx), and OVx + 17β-estradiol (OVx + E) myocytes. The activation curve was plotted using the test voltage and the corresponding normalized conductance (G/G_max). Conductance (G) was calculated using the following equation: G = I/(V − V_rev), where V was the test voltage, I was the peak current at the test voltage, and V_rev was the reversal potential obtained by extrapolating the tail part of the I-V curve to its intersection with the voltage axis. Steady-state inactivation was obtained by normalizing the individual currents to the maximal current (I/I_max) and plotting against the test voltage. A and B: L-type Ca²⁺ channel gating shifted to more positive membrane potential (E_m) in OVx myocytes compared with Sham myocytes (V_{1/2 inactivation} shift: 3.0 mV, P < 0.001). Channel gating was unaltered in OVx + E compared with Sham myocytes. Sham: n = 40/5, OVx: n = 46/6, and OVx + E, n = 37/7. C: the probability of having the channel opening within the “window” range of voltages in Sham myocytes peaked at −15 mV with a probability value of 0.07. This value increased to 0.15 at −10 mV in OVx cells. In OVx + E cells, the probability value was 0.06 at −10 mV.