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

in the present work we studied the intraregional expression of voltage-depe ndent Ca2+ and K+ currents in hair cells of frog crista ampullaris. The cur rents were recorded in situ from sensory cells of the peripheral region, th e most populated region of the crista. by using the whole-cell variant of t he patch-clamp technique. Voltage-clamp recordings revealed that the calciu m current (I-Ca) and the outward potassium currents of I-A, I-K, I-KCa type s and the inward rectifier potassium current of I-KI type exhibited a signi ficant gradient of density (pA/pF) along the region. I-A density was maxima l in cells located at the beginning of the peripheral region and decreased gradually becoming very small at the opposite end. All the other currents s howed an opposite gradient of expression. Current-clamp experiments showed that the voltage behaviour of hair cells changed in relation to cell positi on. Cells located at the beginning of the peripheral region showed large de polarizations from the resting potential (close to -45 mV) which are consis tent with the presence of small I-K and I-KCa and an I-A largely inactivate d at rest. These cells also exhibited slowly developing and large hyperpola rizations that approached passive ones, due to the lack of I-KI. In contras t. cells located at the opposite side of the region showed smaller depolari zations and hyperpolarizations from the resting potential (close to -65 mV) , due to the presence of large I-K and I-KCa and I-KI, respectively. The po ssible role of the intraregional variation of Ca2+ and K+ currents in both hair cell function and afferent discharge properties is discussed.