Niflumic acid hyperpolarizes smooth muscle cells via calcium-activated potassium channel in spiral modiolar artery of guinea pigs

Aim： The influence of niflumic acid （NFA）, a C^1- channel antagonist, on the membrane potentials in smooth muscle cells （SMC） of the cochlear spiral modiolar artery （SMA） in guinea pigs was examined. Methods： The intracellular recording and whole-cell recording technique were used to record the NFA-induced response on the acutely-isolated SMA preparation. Results： The SMC had 2 stable but mutually convertible levels of resting potentials （RP）, that is, one was near -45 mV and the other was approximately -75 mV, termed as low and high RP, respectively. The bath application of NFA could cause a hyperpolarization in all the low RP cells, but had little effect on high RP cells. The induced responses were concentration-dependent. Large concentrations of NFA （≥100 μmol/L） often induced a shift of a low RP to high RP in cells with an initial RP at low level, and NFA （up to 100 μmol/L） had little effect on the membrane potentials of the high RP cells. However, when the high RP cells were depolarized to a level beyond -45 mV by barium and ouabain, NFA hyperpolarized these cells with the similar effect on those cells initially being the low RP. The NFA-induced response was almost completely blocked by charybdotoxin, iberiotoxin, tetraethylammonium, 1,2-bis（2- aminophenoxy） ethane-N,N,N＇,N＇-tetraacetic acid tetrakis acetoxymethyl ester, but not by 4-aminopyridine, barium, glipizide, apamin, ouabain, and CdC12. Conclusion： NFA induces a concentration-dependent reversible hyperpolarization in SMC in the cochlear SMA via activation of the Ca^2＋-activated potassium channels.