Extracellular pH Modulates the Voltage-dependent Ca2+ Current and Low Threshold K+ Current in Hair Cells
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Extracellular protons have been shown to modulate voltage-activated ionic channels. It has been proposed that synaptic modulation by exocytosed vesicular protons would be a characteristic feature of ribbon-type synapses. Type-I hair cells have a calyceal afferent junction with a diffusionally restricted synaptic cleft. These led us to study the action of extracellular pH changes on the voltage-activated Ca2+ and K+ currents evaluated using a whole-cell patch clamp in isolated cells. The amplitude of the Ca2+ and the K+ current were reduced by extracellular acidification, but without significant changes with extracellular alkalization. A shift in the voltage dependence to a more positive membrane potential was achieved at pH < 6.8. Our results shows that the presynaptic K+ and Ca2+ currents are modulated by protons, indicating that protons released along with an afferent neurotransmitter would participate as a feedback mechanism in type-I hair cells.