β2 and β4 Subunits of BK Channels Confer Differential Sensitivity to Acute Modulation by Steroid Hormones

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Abstract
Membrane-associated receptors for rapid, steroidal neuromodulation remain elusive. Estradiol has been reported to facilitate activation of voltage- and Ca2+-dependent BK potassium channels encoded by Slo, if associated with β1 subunits. We show here that 1) multiple members of the β family confer sensitivity to multiple steroids on BK channels, 2) that β subunits differentiate between steroids, and 3) that different βs have distinct relative preferences for particular steroids. Expressed in HEK 293 cells, inside-out patches with channels composed of Slo-α alone showed no steroid sensitivity. Cells expressing αβ4 exhibited potent, rapid, reversible, and dose-dependent potentiation by corticosterone (CORT; a glucocorticoid), and were potentiated to a lesser degree by other sex and stress steroids. In contrast, αβ2 channels were potentiated more strongly by dehydroepiandrosterone (DHEA; an enigmatic, stress-related adrenal androgen), and to a lesser extent by CORT, estradiol, testosterone, and DHEA-S. Cholesterol had no effect on any BK channel compositions tested. Conductance–voltage plots of channels composed of α plus β2 or β4 subunits were shifted in the negative direction by steroids, indicating greater activation at negative voltages. Thus our results argue that the variety of Slo-β subunit coexpression patterns occurring in vivo expands the repertoire of Slo channel gating in yet another dimension not fully appreciated, rendering BK gating responsive to dynamic fluctuations in a multiple of steroid hormones.
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