Low-voltage activated (LVA) inward current in murine antral smooth muscle cells is an artifact

Abstract

We characterized the two types of voltage-dependent inward currents in murine antral SMC. The HVA and LVA inward currents were identified when cells were bathed in Ca2+-containing physiological salt solution. We examined whether the LVA inward current was due to: 1) T-type Ca2+ channels, 2) Ca2+-activated Cl- channels, 3) non-selective cation channels (NSCC) or 4) voltage-dependent K+ channels with internal Cs+-rich solution. Replacement of external Ca2+ (2 mM) with equimolar Ba2+ increased the amplitude of the HVA current but blocked the LVA current. Nicardipine blocked the HVA current, and in the presence of nicardipine, T-type Ca2+ blockers failed to block LVA. The Cl- channel antagonist had little effect on LVA. Cation-free external solution completely abolished both HVA and LVA. Addition of Ca2+ in cation-free solution restored only HVA currents. Addition of K+ (5 mM) to cation-free solution induced LVA current that reversed at -20 mV. These data suggest that LVA is not due to T-type Ca2+ channels, Ca2+-activated Cl- channels or NSCC. Antral SMC express A-type K+ currents (KA) and delayed rectifying K+ currents (KV) with dialysis of high K+ (140 mM) solution. When cells were exposed to high K+ external solution with dialysis of Cs+-rich solution in the presence of nicardipine, LVA was evoked and reversed at positive potentials. These HK-induced inward currents were blocked by K+ channel blockers, 4-aminopyridine and TEA. In conclusion, LVA inward currents can be generated by K+ influx via KA and KV channels in murine antral SMC when cells were dialyzed with Cs+-rich solution.