Fig. 4.

Ionic selectivity of the ciliary large-conductance channel. Mean single-channel current-voltage relations were determined in solutions as described (Table 1). A: symmetrical high-K⁺ solutions. The pipette contained the high-K⁺ external solution, and high-K⁺ cytoplasmic solutions were used (0.1 to 300 µM free Ca²⁺). Single-channel currents were measured in 11 cilia as described for Fig. 3C. Single-channel conductance 189 pS; reversal potential −1.0 mV. B: test of relative Cl¯ permeability. The pipette contained the high-K⁺ external solution, and Cl¯-free cytoplasmic solutions (which also have high K⁺) were used (3 µM or 300 µM free Ca²⁺). Single-channel currents were measured in 5 cilia. Single-channel conductance 185 pS; reversal potential 0.0 mV. C: test of relative Na⁺ permeability. The pipette contained the high-K⁺ external solution, and high-Na⁺ cytoplasmic solutions were used (3 µM or 300 µM free Ca²⁺). Single-channel currents were measured in 4 cilia. Single-channel conductance 126 pS; reversal potential +42 mV. D: test of Ca²⁺ permeability. The pipette contained the high-Ca⁺ external solution, and high-K⁺ cytoplasmic solutions were used (0.1, 3, or 300 µM free Ca²⁺). Single-channel currents were measured in 7 cilia. Single-channel conductance 114 pS; reversal potential −13 mV.