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

Abstract

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 (Ginput) or increased the input resistance (Rinput) in a concentration dependent manner, with slightly different IC50s 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 (BKCa) 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 BKCa, suppressed the enhancement of the BKCa by FFA and NFA. The KV 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 BKCa channels in the arteriolar smooth muscle cells in addition to their known inhibitory effects on chloride channels.

Primary Cultivation and Identification of Vascular Smooth Muscle Cells from the Spiral Modiolar Artery of Guinea Pigs

“…We also recorded the scatter plot of the resting membrane potential of P3 and P6 from SMCs (Figure 12). These results were consistent with the experimental results of previous studies [20–22].…”

Enhanced expression of Cx43 and gap junction communication in vascular smooth muscle cells of spontaneously hypertensive rats

“…NFA, a fenamate, which inhibits cyclooxygenase-2, is commonly used as a non-steroidal anti-inflammatory drug in patients. In previous studies, it was found that NFA at 3×10 −4 M completely inhibited the leakage current and strengthened current components of BK Ca (42). The whole-cell patch clamp experiment performed in the present study demonstrated that C input and G input were reduced by NFA, further indicating that NFA was able to inhibit the GJ communication among VSMCs.…”

The role of Ca2+-activated Cl− current in tone generation in the rabbit corpus cavernosum

“…However, the conventional Cl Ϫ channel antagonists, niflumic acid and A9C, were very weak blockers of this current, especially of inward Cl Ϫ current, which is the relevant direction for depolarization (11). These compounds also suffer from a variety of unwanted effects, with reports that both drugs interfere with intracellular Ca 2ϩ release (12), activate BK channels (15,24,35), and block cation channels (8,19,34), while niflumic acid also blocks Tand L-type Ca 2ϩ currents (3,38), fast voltage-dependent Na ϩ current (4,39), and gap junction coupling (24) and has been widely used as a nonsteroidal anti-inflammatory drug (NSAID) because of its blocking action on cyclo-oxygenase-2 (COX-2; 22). Therefore, although high concentrations of these compounds have been reported to reduce catecholamine-and nerve-evoked contractions in rabbit corpus cavernosum (9,23), and to increase intracorporeal pressure in rats and rabbits (21), their lack of potency and specificity make these experiments difficult to interpret.…”