Fenamates block gap junction coupling and potentiate BK_Ca channels in guinea pig arteriolar cells

We determined the actions of the fenamates, flufenamic acid (FFA) and niflumic acid (NFA), on gap junction-mediated intercellular coupling between vascular smooth muscle cells (VSMC) in situ of acutely isolated arteriole segments from the three vascular beds: the spiral modiolar artery (SMA), anterior inferior cerebellar artery (AICA) and mesenteric artery (MA), and on non-junctional membrane channels in dispersed VSMCs. Conventional whole-cell recording methods were used. FFA reversibly suppressed the input conductance (G_input) or increased the input resistance (R_input) in a concentration dependent manner, with slightly different IC_50s for the SMA, AICA and MA segments (26, 33 and 56 μM respectively, P>0.05). Complete electrical isolation of the recorded VSMC was normally reached at ≥300 μM. NFA had a similar effect on gap junction among VSMCs with an IC₅₀ of 40, 48 and 62 μM in SMA, AICA and MA segments, respectively. In dispersed VSMCs, FFA and NFA increased outward rectifier K ⁺-current mediated by the big conductance calcium-activated potassium channel (BK_Ca) in a concentration-dependent manner, with a similar EC₅₀ of ∼300 μM for both FFA and NFA in the three vessels. Iberiotoxin, a selective blocker of the BK_Ca, suppressed the enhancement of the BK_Ca by FFA and NFA. The K_V blocker 4-AP had no effect on the fenamates-induced K⁺-current enhancement. We conclude that FFA and NFA blocked the vascular gap junction mediated electrical couplings uniformly in arterioles of the three vascular beds, and complete electrical isolation of the recorded VSMC is obtained at ≧300 μM; FFA and NFA also activate BK_Ca channels in the arteriolar smooth muscle cells in addition to their known inhibitory effects on chloride channels.