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

Abstract

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.

Potassium currents in the hair cells of vestibular epithelium: position‐dependent expression of two types of A channels

“…By contrast, PR hair cells showed variations in the magnitude of inwardly rectifying K + currents and in the time course of outward K + currents in relation to the position of the section along the region. This is consistent with our previous data in longitudinal slices indicating the presence of variations in the amplitude of the various K + currents in relation to the cell position (Russo et al ., 2001). Most interestingly, outward K + currents also changed within each slice: their inactivation became progressively more rapid from the median part of the slice towards its edges.…”

“…To measure input resistance, cells were bathed in Ringer's solution containing 5 m m Cs 2+ , in order to block inward rectifier channels, and then hyperpolarized by 10 mV starting from a holding potential of −70 mV. Detailed descriptions of the recording procedures are described elsewhere (Masetto et al ., 1994; Russo et al ., 2001).…”

“…In the frog, we have provided evidence that three discrete regions of the crista (peripheral, intermediate and central regions) have hair cell types that differ both in shape and in complement of voltage‐dependent K + conductances (Masetto et al ., 1994; Prigioni et al ., 1996). In addition, a gradient in amplitude of both K + currents and a Ca 2+ current (I Ca ) has been found within the peripheral regions (Russo et al ., 2001, 2003). Comparable results have been obtained in the avian and turtle crista (Masetto & Correia, 1997; Weng & Correia, 1999; Brichta et al ., 2002; Goldberg & Brichta, 2002).…”

Nature and expression of dihydropyridine-sensitive and -insensitive calcium currents in hair cells of frog semicircular canals

“…In the semicircular canals of frogs and birds, hair cells positioned in discrete regions of the crista exhibit differences in the expression of their K + conductances [18,19,28,42]. Moreover, a gradient in amplitude of both K + and Ba 2+ currents has also been found within the peripheral region in the crista ampullaris of the frog [15,36]. The notion is that the sensory cells of the vertebrate crista ampullaris exhibit both regional and intraregional variations in the expression of voltage-gated channels.…”

Ca2+ currents and voltage responses in Type I and Type II hair cells of the chick embryo semicircular canal

“…Moreover, Type I hair cells only express a low-voltage activated outward rectifying K + current, called I K,L , which can be considered their ''signature'' current [48,55]. At the same time, vestibular Type II hair cells are not all alike, since the expression of voltage-dependent ion currents varies depending on cell location in the epithelium both in lower vertebrates [7,35,36,47,57,61] and birds [31,37,63].…”