Abstract
Externally applied ATP (100 μM) 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 Ca 2+ levels were monitored using the Ca 2+ 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 Ca 2+ into crista hair cells which can then further modulate K + currents.
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