Figure 2. Effects of mutations at Glu236 and Met313 on m₂R-dependent activation.

A. Typical current traces of Kir3.2 wild-type (WT) and mutant channels recorded in the presence of various concentrations of ACh. The current responses were elicited by a test pulse at −120 mV for 0.6 s followed by a voltage step to +40 mV for 0.6 s at an interval of 0.1 s at −20 mV. This sequence was repeated every 3 s. The current in the presence of 3 mM Ba²⁺ was subtracted from each trace. The arrowheads indicate the zero current levels.

B, C. Current response of Kir3.2 WT and mutant channels. ACh-induced K⁺ currents recorded at the end of the test pulse to −120 mV were normalized to that measured in the presence of 10 μM ACh. Error bars indicate the standard error of the mean. The current responses of the WT and mutants were fit using the Hill equation as described in the Materials and Methods section.