Fig. 4.

Single-channel currents from the wild-type and mutant receptors activated by 3 μM ACh. A, the currents were recorded from a HEK cell stably expressing the human α3β4 receptors. The stably expressing α3β4 cells were used in transient transfections with wild-type (B) and mutant (C–E) α5 subunits. The wild-type and mutant α5 subunits contained a FLAG epitope inserted at the amino terminus of the subunit. Cells expressing the α5 subunit were selected with immunobeads coated with anti-FLAG antibody. The currents were recorded in the cell-attached configuration. Channel openings are shown as downward deflections. The intraburst open times were fitted with a single exponential. The mean open times were 13.3 ms (A), 2.7 ms (B), 4.3 ms (C), 7.1 ms (D), and 9.7 ms (E). The average open times from multiple patches are given in the text. The intraburst closed-time durations are given in Table 3. F, cumulative open-time distribution histograms. The addition of the α5 subunit results in briefer open-time durations (left). The introduction of the V9′S mutation to the α5 subunit results in longer open time durations (right).