K ⁺ _o sensitivity of nonselective T312C mutant. (A) Sample current traces of the T312C mutant recorded in 100 mM external Na⁺, K⁺, and Rb⁺ (black traces) solutions to calculate reversal potential changes. Recordings from water-injected oocytes from the parallel batch under identical conditions are shown in gray. (B) Instantaneous current–voltage curves after correction for average leak current from water-injected oocytes. Three separate batches of oocytes were injected with T312C cRNA from two separate syntheses. Results of statistical analysis of reversal potential changes are shown in the text, n = 9, error bars represent ±SEM. (C) Representative current traces of T312C (black) and the corresponding water-injected oocytes (gray) upon exchange of monovalent cations in extracellular solution as indicated. (D) Analysis of peak and tail current amplitudes shown in C normalized to Na⁺. Leak currents were estimated using a parallel batch of oocytes, n = 4, error bars represent ± SEM.