Ca²⁺ dose response of I_MCU. (A) I–V curves of I_MCU in various external [Ca²⁺]. (B) A dose–response plot. Currents (measured at −120 mV) induced by 2, 5, 10, and 50 mM Ca²⁺ were normalized to currents induced by 20 mM Ca²⁺. A Michaelis-Menten equation was used for data fit (red curve). Each data point represents five to eight repeats. Data are presented as mean ± SEM.