Figure 2.
Multiple kinetic components of chick cochlear hair cell exocytosis. A. Depolarizing stimulus of 100-ms duration elicits a step increase in membrane capacitance (Cm) independent of changes in membrane conductance (Gm) or series conductance (Gs). Traces are blanked during the depolarizing voltage clamp step, as the capacitance measurements are not valid due to large changes in Gm (Lindau and Neher 1988)
. B. A 300-ms depolarization results in a larger step change in Cm. Changes in Gm also were observed. However, such changes in Gm appeared to be well separated from changes in Cm by the lock-in amplifier since the increase in Gm did not correlate in magnitude or time course with the change in Cm and likely resulted from calcium-activated channel activity (see Fig. 3). Nonetheless, capacitance traces were measured 100 ms after the end of the depolarizing pulse to avoid any contamination of the exocytotic response by capacitive transients not associated with exocytosis (Horrigan and Bookman 1994; Debus et al. 1995). C. The results of several experiments like A and B are summarized. The mean value and SEM os ΔCm are plotted versus stimulus duration.