OBJECTIVETo explore the dependence of Ca2+ on the acetylcholine (ACh)-sensitive potassium current in guinea pig type II vestibular hair cells.

METHODSUnder the whole-cell patch mode, the current amplitude of the ACh-sensitive potassium current was recorded in response to the concentration change of the extracellular or intracellular Ca2+.

RESULTSFollowing application of ACh, type II vestibular hair cells displayed the sustained potassium current, which was inhibited by tetraethylammonium chloride (TEA), but not inhibited by 4-aminopyrine (4-AP). The activation of the ACh-sensitive potassium current was strongly affected by the concentration of the extracellular Ca2+. The current amplitude of the ACh-sensitive potassium increased following the increase of Ca2+ concentration from 0 mmol/L to 4 mmol/L At the concentration of 4 mmol/L Ca2+, the current amplitude of the ACh-sensitive potassium current reached the maximal response. Lowering the Ca2 concentration in the external solution from 4 mmol/L to 0. 5 mmol/L, the current amplitude of the ACh-sensitive potassium current was inhibited to (36.5 +/- 6.5)%. However, no difference was found in the presence and in the absence of the intracellular heparin, which was a well-known blocker of the inositol trisphosphate-dependent calcium release channels. In addition, the calcium channel blocker, Cd2+, inhibited the ACh-sensitive potassium current.

CONCLUSIONSThe activation of the ACh-sensitive potassium current in guinea pig type II vestibular hair cells was dependent on the extracellular Ca2+ influx through the calcium channel. The application of ACh would stimulate membrane Ca2+ channels; the influx of Ca2+ will then activate the calcium-dependent potassium current in guinea pig type II hair cells to mediate the hyperpolarization effect.