Voltage-clamp recordings from single renal primary cilia. All recordings were made in the standard recording solutions except as noted. In A and C, dashed lines indicate the current level when the channels were closed. (A) Single-channel fluctuations were recorded while the cilium in the pipette was still attached to the cell. Pipette potential was strongly depolarizing (−140 mV). (B) Membrane current–voltage relations of two cilia after excision from the cell. The recording shown in black has an input resistance R = 10.1 GΩ. In the recording shown in blue (R = 7.4 GΩ), single-channel openings are visible at potentials more positive than +50 mV. (C) Activation by Ca2+ and by depolarization of large-conductance channels in an excised renal primary cilium. On the left are shown the membrane currents at three voltage-clamp potentials in the presence of 0.1 μM free cytoplasmic Ca2+. On the right are recordings with 3 μM free cytoplasmic Ca2+ present. (D) A macroscopic current activated by high cytoplasmic Ca2+ in an excised cilium. The current–voltage relation was measured in each of two pseudointracellular baths: a bath containing 0.1 μM Ca2+ (black); and a bath with 300 μM Ca2+ (red).