Functional effects of MTSEA and MTSET modification of Kir2.1*-169C dimeric channels. Inside-out patches expressing the Kir2.1*-169C dimer were pulsed between −100 and +50 mV in control or 100 µM spermine. Pulse protocols were repeated after steady-state modification with either (A) MTSEA or (B) MTSET. For simple comparison between control and spermine conditions, pulses to −20 and −10 mV have been highlighted in red and blue, respectively. (C) Conductance–voltage relationships illustrate the voltage dependence of block in control (n = 13) or after modification with either MTSEA (n = 5) or MTSET (n = 7). Mean data were fit with the three-state model described in Materials and methods. (D) Schematic representation of the Kir channel inner cavity, illustrating the spatial relationship between position 169C and the spermine binding site hypothesized from studies in Kir6.2[N160D] channels (Kurata et al., 2006).