Fig. 5.

Voltage and Ca²⁺ sensitivity of transmitter release. (A) Recordings during a simultaneous voltage-clamp experiment depict presynaptic Ca²⁺ currents (middle traces) and EPSCs (bottom traces) evoked by 100-ms hair-cell depolarizations (top traces). (B) Both the presynaptic Ca²⁺ current (circles) and the postsynaptic current (triangles) display a sigmoidal dependence on the test potential. Data are presented as normalized means ± standard errors of the means for four experiments. (C) In each of four paired recordings, the dependence of the postsynaptic current on the presynaptic Ca²⁺ current is approximately linear over a physiologically relevant range of hair-cell membrane potentials, here −56 mV to −31 mV. Clockwise from the upper left, the linear regression coefficients (r²) are 0.88, 0.97, 0.97, and 0.95.