FIGURE 4.

The N160D subunit marker of strong spermine block only slightly slows gating to the inactive interburst. (A) Single-channel record of a representative K_ir6.2ΔC26/160D channel. (B) Duration histogram of the burst times shows the relatively mild effect of the 160D mutation on gating. (C) Single-channel record of a representative K_ir6.2ΔC26/171A/160D double mutant channel. (D) Duration histogram of the burst times shows a dramatic increase in the burst times of the K_ir6.2ΔC26/171A/160D double mutant channel. The slowing of gating by all our T171 mutations, as shown here by 171A, is dramatic compared to that of 160D. In these experiments, both the 160D and 171A mutations were in all four subunits. The effect of T171A predominantly determines both K_i,ATP and burst to interburst gating rates in the channels.