Vladimir Matchkov

We have recently characterized a cGMP-dependent Ca²⁺-activated Cl^- current (I_Cl,cGMP) with unique characteristics in smooth muscle cells (SMCs) and suggested that this could be important for vasomotion in mesenteric arteries. We hypothesized that a bestrophin could be responsible for I_Cl,cGMP based on similarities in the membrane currents and on the distribution pattern of I_Cl,cGMP and bestrophin-3 protein expression in different SMCs.

Bestrophin-3 was downregulated with small interference (siRNA) in rat mesenteric small arteries in vivo. Non-related siRNA and mutated bestrophin-3 siRNA were used as the controls.

Downregulation induced by specific siRNA was evident by reduced expression of bestrophin-3 mRNA and protein (to 24+/-17 % and to 58+/-9 % of the control, n=3) without an effect on other bestrophin isoforms. SMCs downregulated for bestrophin-3 demonstrated a significant reduction of I_Cl,cGMP (by 98+/-0.2%, n=7 at -60 mV), while the “classical” Ca²⁺-activated Cl^- current was unaffected. Surprisingly, arteries with reduced bestrophin-3 were more sensitive to noradrenaline than control vessels. The downregulation of bestrophin-3 significantly reduced the amplitude of arterial vasomotion (by 75+/-10 % n=6) without significant effect on frequency.

We provide evidence that bestrophin-3 is essential for I_Cl,cGMP and is important for generation of vasomotion in rat mesenteric small arteries.

This work was supported by the Danish Research Council, the Danish Heart Foundation. The Water and Salt Research Center at the University of Aarhus is established and supported by the Danish National Research Foundation.