Activation of R190 mutant Slo2.1 channels by NFA or Na_i loading in oocytes bathed in high K⁺ extracellular solution. (A) I-V relationships for R190E Slo2.1 channels recorded using the indicated extracellular solutions. Currents were recorded from the same oocyte as extracellular solution was changed in the order (from top to bottom) indicated in the symbol legend. Oocytes were recorded 1 d after injection with 0.84 ng cRNA (n = 8). After recording currents when oocytes were bathed in KCM211 and K104 solutions, oocytes were then incubated in Na_i-loading solution for 15 min before again measuring I-V relationship using K104 solution (“K104, Na_i-loaded”). Finally, the bathing solution was switched to KCM211, and currents were recorded once again (“KCM211, Na_i-loaded”). (B) Example of currents recorded from an oocyte before and after treatment with 1 mM NFA. Arrows indicate 0 current level. (C) I-V relationships for R190E Slo2.1 channels recorded from oocytes bathed in K104 extracellular solutions before and after treatment with 1 mM NFA. Oocytes were recorded 1 d after injection with 0.84 ng cRNA (n = 6). (D and E) I-V relationships for R190A (D) and R190Q (E) Slo2.1 channels recorded from oocytes bathed in K104 extracellular solutions before and after treatment with 1 mM NFA. Oocytes were recorded 1 d after injection with 0.92 ng R190A (n = 8) or 0.32 ng R190Q (n = 10) Slo2.1 cRNA.