Position-dependent expression of inwardly rectifying K+ currents by hair cells of frog semicircular canals

The identity and the expression of inwardly rectifying ionic currents were studied using the whole-cell variant of the patch-clamp technique in frog semicircular canal hair cells in situ. The currents were examined in club-, cylindrical- and pear-shaped sensory cells located in three discrete regions of the crista. A unique current of I(K1) type was distinguished based on its K+ selectivity, rapid monoexponential activation, dependence of activation on external K+ and blockade by Ba2+ and Cs+. I(K1) was found in virtually all cylindrical hair cells of the central region and in club-shaped cells located in the halves of the peripheral regions closest to the centre of the crista. Pear-shaped cells of the intermediate regions showed no inward rectification. The I(K1) density (pA/pF) varied along the crista depending on cell position, being maximal in cells located in the middle of the central region and decreased towards its ends. In the peripheral regions, the gradient of I(K1) increased towards the centre of the crista. Current clamp experiments showed that sensory cells having larger I(K1) constantly exhibited more negative resting potentials and required more depolarizing current to elicit an active response than cells having small or no I(K1).