Rundown of Ano1 current in excised patches. (A) Excised patches were pulled from cells expressing Ano1(ac) and exposed to internal solution containing 1.38, 3.36, 20, and 74.35 µM Ca²⁺. Current amplitudes at 100 mV are plotted versus time in Ca²⁺-containing solution (n = 3–10). The data were fitted to an exponential I_(t) = y₀ + A × e^−t/τ, where t is time in ms and y₀ is the plateau level of rundown. Error bars are ±SEM. (B) The time constant of rundown (τ) and the extent of rundown expressed as y₀ for the data in A are plotted versus free Ca²⁺ in the cytosolic solution.