Estrogen regulates β1-subunit expression in Ca2+-activated K+ channels in arteries from reproductive tissues

Daily estradiol-17 beta (E-2 beta) increases basal uterine blood flow (UBF) and enhances acute E-2 beta-mediated increases in UBF in ovariectomized nonpregnant ewes. The acute E-2 beta-mediated rise in UBF involves vascular smooth muscle (VSM) large-conductance Ca2+-activated K+ channels (BKCa). BKCa consist of pore-forming alpha-subunits and regulatory beta(1)-subunits that modulate channel function and E-2 beta responsiveness. It is unclear whether E-2 beta also alters subunit expression and thus channel density and/or function, thereby contributing to the rise in basal UBF and enhanced UBF responses that follow daily E-2 beta. Therefore, we examined BKCa subunit expression by using reverse transcription-PCR and immunoblot analysis of arterial VSM from reproductive and nonreproductive tissues and myometrium from ovariectomized nonpregnant ewes after daily E-2 beta (1 mu g/kg iv) or vehicle without or with acute E-2 beta (1 mu g/kg). Tissue distribution was determined by immunohistochemistry. Acute E-2 beta did not alter alpha- or beta(1)-subunit expression in any tissue (P>0.1). Daily E-2 beta also did not affect alpha- subunit mRNA or protein in any tissue (P>0.1) or mesenteric arterial VSM beta(1)-subunit. However, daily E-2 beta increased uterine and mammary arterial VSM beta(1)-subunit mRNA by 32% and 83% (P<0.05), uterine VSM protein by 30%, and myometrial beta(1)-subunit mRNA and protein by 74% (P <= 0.005). Immunostaining of uterine arteries, myometrium, and intramyometrial arteries paralleled immunoblot analyses for both subunits. Although BKCa density is unaffected by daily and acute E-2 beta, daily E-2 beta increases beta(1)-subunit in proximal and distal uterine arterial VSM. Thus prolonged E-2 beta exposure may alter BKCa function, estrogen responsiveness, and basal vascular tone and reactivity in reproductive arteries by modifying alpha:beta(1) stoichiometry.