Figure 1. Cl⁻ current activated by longitudinal diffusion of Ca²⁺ from the bath is insensitive to ATP.

(A) A cilium was held for 2 min in a control cytoplasmic bath containing 0.1 µM free Ca²⁺ and 2 mM MgITP. At t = 0 s, the cilium was transferred to a bath containing 300 µM free Ca²⁺ and 2 mM MgITP (recording shown in black). Membrane potential was held at −50 mV. The initial current (−20 pA) is a membrane leak current. The additional current that starts at t = 1.8 s is the Ca²⁺-activated Cl⁻ current. The experiment was repeated in control and test solutions in which MgITP was replaced by MgATP (recording shown in red). Ca²⁺ was buffered in all solutions with 2 mM BAPTA. (B) Summary of the effects of ATP on the onset time of the Cl⁻ current. Normalized onset time is the time measured in the presence of ATP divided by that measured in the control (ITP). The normalized onset times shown are 0.97±0.08 (7 µM free Ca²⁺), 1.13±0.06 (20 µM free Ca²⁺), and 0.97±0.06 (300 µM free Ca²⁺).