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

PEDRO MARTIN; VERONICA MILESI; AGUSTIN ASUAJE; VALENTINA PASTORE

Congreso; 61st Biophysical Society annual meeting; 2017

Thiazide-like diuretics are still recommended as first-line antihypertensivetherapy, based on their chronic vasodilatory effects. Previous studies suggestactivation of the large conductance voltage- and Ca2þ- dependent Kþchannel(BK channel) expressed in vascular smooth muscle cells (SMCs), as responsiblefor this vasodilator effect, but electrophysiological evidence supportingthis is lacking. BK can be accompanied by accessory b-subunits, which conferspecific pharmacological characteristics to the channel. The b1 subunit ismainly expressed in SMCs.We measured the effect of hydrochlorothiazide (HCTZ) on BK channel activityusing the patch-clamp technique in SMCs from human umbilical artery(HUASMCs) and in HEK293 T expressing the BK channel (with and withoutthe beta-1 subunit).In HUASMCs, HCTZ (10 mM) caused significant activation of the BK currentin the whole-cell configuration (5285215 to 13795132 pA at þ40mV, n: 4,p 0.05), suggestingan indirect activation mechanism. In HEK cells expressing the BKchannel (with and without b1-subunit), HCTZ only activates BK channel inthe 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 potentialdid not influence the concentration relationship on HCTZ-induced BK channelactivation. Consistently, HCTZ did not change the BK channel activity when itwas 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 anindirect activation of the BK channel depending on the beta-1 subunitexpression.