Figure 7.

Effect of [Na⁺] on ouabain-sensitive currents at pH 5.0. (A) Excerpt traces from a continuous recording from an oocyte where 0, 1, 2, 5, 12, 25, 50, and 120 mM Na⁺ were tested. Each application of pH 5.0 solution was preceded by an application of 3 mM K⁺ to ensure that the total number of pumps did not change. Applications of 1, 5, and 12 mM are shown after stabilization of I_H at pH 5.0. Ouabain was then added in the presence of Na⁺ and Na⁺ was then removed in the presence of steroid. Ouabain was washed out for 15 min in 120 mM Na⁺ (pH 7.6) before the next maneuver. (B) Full dose response for current activation at −160 mV in the oocyte shown in A. (C) Mean ± SE) at −160 mV, normalized to the steady-state current at 0 Na⁺, at concentrations where n > 8.