17β-Estradiol attenuates voltage-dependent Ca²⁺ currents in A7r5 vascular smooth muscle cell line

Previous studies have shown that 17β-estradiol (β-E₂) has a direct acute inhibitory effect on vascular smooth muscle (VSM) contraction. To investigate the mechanisms underlying this phenomenon, we utilized whole cell patch-clamping techniques to study effects of β-E₂ on voltage-dependent Ca²⁺ channels in cultured VSM cells (VSMC). T- and L-type Ca²⁺ currents were characterized with ramp and pulse protocols in A7r5 cultured VSMC. T- type current, inactivated in < 100 ms, was reduced by Ba²⁺ and was comparatively little affected by isradipine. L-type current required higher voltages to activate, inactivated slowly, was greatly increased by Ba²⁺, and could be completely inhibited by 5 μM isradipine. β-E₂ (10 μM) significantly reduced peak L-type Ba²⁺ current and T-type Ca²⁺-current within 1-2 min, whereas α-E₂ (a hormonally inactive isomer of estradiol) caused significantly less reduction in both types of current. Vehicle (0.1% ethanol) had no significant effect on either current. The inhibitory effect of β-E₂ on voltage-dependent Ca²⁺ currents may contribute to previously demonstrated β-E₂ attenuation of VSM contraction.