Gradients of expression of calcium and potassium currents in frog crista ampullaris

In the present work we studied the intraregional expression of voltage-dependent Ca2+ and K+ currents in hair cells of frog crista ampullaris. The currents were recorded in situ from sensory cells of the peripheral region, the most populated region of the crista, by using the whole-cell variant of the patch-clamp technique. Voltage-clamp recordings revealed that the calcium current (I(Ca)) and the outward potassium currents of I(A), I(K) I(KCa) types and the inward rectifier potassium current of I(K1) type exhibited a significant gradient of density (pA/pF) along the region. I(A) density was maximal in cells located at the beginning of the peripheral region and decreased gradually becoming very small at the opposite end. All the other currents showed an opposite gradient of expression. Current-clamp experiments showed that the voltage behaviour of hair cells changed in relation to cell position. Cells located at the beginning of the peripheral region showed large depolarizations from the resting potential (close to -45 mV) which are consistent with the presence of small I(K) and I(KCa), and an I(A) largely inactivated at rest. These cells also exhibited slowly developing and large hyperpolarizations that approached passive ones, due to the lack of I(K1). In contrast, cells located at the opposite side of the region showed smaller depolarizations and hyperpolarizations from the resting potential (close to -65 mV), due to the presence of large I(K) and I(KCa), and I(K1), respectively. The possible role of the intraregional variation of Ca2+ and K+ currents in both hair cell function and afferent discharge properties is discussed.