Fig. 3.

Large-conductance channels in excised single cilia. A: current fluctuations from opening and closing of single channels at +80 mV. Numbers at the right of each recording indicate the number of channels open at each current level; the levels are indicated by dashed lines. The standard external solution was used to bathe the cell and to fill the pipette; the cytoplasmic solution was the standard solution, which contained 0.1 µM free Ca²⁺. B: an amplitude histogram from the full 20 s of recorded current. At least 3 channels were present in this cilium. (A peak corresponding to 3 channels was present but too small to be seen at the scale shown.) The average single-channel current was 12.2 pA. C: single-channel current-voltage relation. In each of 66 cilia, single-channel current amplitudes were determined from amplitude histograms of 20-s recordings as in A and B. In many cilia, single-channel currents were measured at each of several voltages. In all cases, the standard external solution was used. For each measurement, single-channel current was determined as shown in A and B. Solutions were as in A, except that cytoplasmic free Ca²⁺ ranged from 0.1 to 300 µM. The mean single-channel conductance (slope) is 97 pS, and the reversal potential (x-intercept) is −61 mV.