Effects of extracellular ATP on hair cells isolated from the guinea-pig semicircular canals.

ABSTRACT

Externally applied ATP (100 microM) induced membrane currents in type I and type II vestibular hair cells enzymatically isolated from guinea-pig semicircular canals. In whole-cell voltage-clamp and with 140 mM K+ in the pipette solution, ATP evoked an inwardly directed current in 58% of the cells when held at potentials below -40 mV. In the remainder, external ATP produced an outward current. After block of the K currents, an inward current activated by ATP was revealed at -50 mV. Intracellular Ca2+ levels were monitored using the Ca2+ indicator Fura-2 and were found to rise in both hair cell types in response to ATP. These results strongly suggest that ATP directly controls the entry of Ca2+ into crista hair cells which can then further modulate K+ currents.