[Dependence of Ca2+ on the acetylcholine-sensitive current in guinea pig type II vestibular hair cells].

Objective To explore the dependence of Ca~ 2+ on the acetylcholine (ACh)-sensitive potassium current in guinea pig type Ⅱ vestibular hair cells. Methods Under 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 Ca~ 2+ . Results Following 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-aminopyride (4-AP). The activation of the ACh-sensitive potassium current was strongly affected by the concentration of the extracellular Ca~ 2+ . The current amplitude of the ACh-sensitive potassium increased following the increase of Ca~ 2+ concentration from 0 mmol/L to 4 mmol/L. At the concentration of 4 mmol/L Ca~ 2+ , the current amplitude of the ACh-sensitive potassium current reached the maximal response. Lowering the Ca~ 2+ 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, Cd~ 2+ , inhibited the ACh-sensitive potassium current. Conclusions The activation of the ACh-sensitive potassium current in guinea pig type II vestibular hair cells was dependent on the extracellular Ca~ 2+ influx through the calcium channel. The application of ACh would stimulate membrane Ca~ 2+ channels; the influx of Ca~ 2+ will then activate the calcium-dependent potassium current in guinea pig type II hair cells to mediate the hyperpolarization effect.