Functional effects of MTSEA and MTSET modification of Kir2.1*-176C dimeric channels. Block by 100 µM spermine was assessed in inside-out patches expressing Kir2.1*-176C dimeric channels, as described in Fig. 2, before and after modification with (A) MTSEA or (B) MTSET. Voltage pulses to −20 and −10 mV are highlighted in red and blue, respectively. (C) Conductance–voltage relationships illustrate the voltage dependence of block in control (n = 14), or after modification with either MTSEA (n = 7) or MTSET (n = 7), and fits are of the three-state model described in Materials and methods. (D) Schematic representation of the Kir channel inner cavity, illustrating the spatial relationship between position 176C and the spermine binding site hypothesized from studies in Kir6.2[N160D] channels (Kurata et al., 2006).