Fig. 3. Direct effects of [Ca²⁺]_i on ENaC activity. In an inside-out recording, 500 nmol l^–1 Ca²⁺ led to maximum ENaC open probability (P_o) and even 5 µmol l^–1 Ca²⁺ exerted significant inhibition on ENaC P_o. The inhibitory effect of Ca²⁺ on ENaC activity depended on the Ca²⁺ concentration. In the lower panels selected currents are shown on an expanded time scale.