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Estrogen regulates ₁-subunit expression in Ca²⁺-activated K⁺ channels in arteries from reproductive tissues

Department of Pediatrics, Division of Neonatal-Perinatal Medicine, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas

Submitted 22 November 2004 ; accepted in final form 13 May 2005

Daily estradiol-17 (E₂) increases basal uterine blood flow (UBF) and enhances acute E₂-mediated increases in UBF in ovariectomized nonpregnant ewes. The acute E₂-mediated rise in UBF involves vascular smooth muscle (VSM) large-conductance Ca²⁺-activated K⁺ channels (BK_Ca). BK_Ca consist of pore-forming -subunits and regulatory ₁-subunits that modulate channel function and E₂ responsiveness. It is unclear whether E₂ 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 E₂. Therefore, we examined BK_Ca 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 E₂ (1 µg/kg iv) or vehicle without or with acute E₂ (1 µg/kg). Tissue distribution was determined by immunohistochemistry. Acute E₂ did not alter - or ₁-subunit expression in any tissue (P > 0.1). Daily E₂ also did not affect -subunit mRNA or protein in any tissue (P > 0.1) or mesenteric arterial VSM ₁-subunit. However, daily E₂ increased uterine and mammary arterial VSM ₁-subunit mRNA by 32% and 83% (P < 0.05), uterine VSM protein by 30%, and myometrial 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 BK_Ca density is unaffected by daily and acute E₂, daily E₂ increases ₁-subunit in proximal and distal uterine arterial VSM. Thus prolonged E₂ exposure may alter BK_Ca function, estrogen responsiveness, and basal vascular tone and reactivity in reproductive arteries by modifying :₁ stoichiometry.

myometrium; nonpregnant ewes; vasodilation; uterine blood flow; mesenteric artery; mammary artery

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