BK Channel Activation in Chronic Vasodilation by Thiazide-Like Diuretics: Role of the Beta-1 Auxiliary Subunit

MARTÍN, P; ASUAJE, A; PASTORE, V; MILESI, V

Nueva Orleans

Congreso; 61st Biophysical Society annual meeting; 2017

Biophysical Society

Thiazide-like diuretics are still recommended as first-line antihypertensive therapy, based on their chronic vasodilatory effects. Previous studies suggest activation of the large conductance voltage- and Ca2+- dependent K+ channel (BK channel) expressed in vascular smooth muscle cells (SMCs), as responsible for this vasodilator effect, but electrophysiological evidence supporting this is lacking. BK can be accompanied by accessory b-subunits, which confer specific pharmacological characteristics to the channel. The b1 subunit is mainly expressed in SMCs. We measured the effect of hydrochlorothiazide (HCTZ) on BK channel activity using the patch-clamp technique in SMCs from human umbilical artery (HUASMCs) and in HEK293 T expressing the BK channel (with and without the beta-1 subunit). In HUASMCs, HCTZ (10 mM) caused significant activation of the BK current in the whole-cell configuration (5285215 to 13795132 pA at +40mV, n: 4, p <0.05), while, it did not produce any changes in BK channel unitary conductance nor open probability in the inside-out configuration (NPo at þ 40mV: 0.0114 5 0.0015 (control) vs 0.0135 5 0.0037 (HCTZ), n: 4, P> 0.05), suggesting an indirect activation mechanism. In HEK cells expressing the BK channel (with and without b1-subunit), HCTZ only activates BK channel in the presence of the b1-subunit. This activation was concentration-dependentwith an EC50 of 28 mM (pD2=4.546 5 0.211, n: 5-8). Membrane potential did not influence the concentration relationship on HCTZ-induced BK channel activation. Consistently, HCTZ did not change the BK channel activity when it was evaluated in HEK cells expressing the b1-subunit in the inside-out configuration, where cell integrity is lost. These results suggest that the vasodilatory effects of HCTZ could be due to an indirect activation of the BK channel depending on the beta-1 subunit expression.