Figure 8. Channel blockade of oocyte-expressed α3 AChR single channel currents by hexamethonium or mecamylamine.

A, all α3 subunit combinations were sensitive to inhibition by hexamethonium or mecamylamine. α3β2 and α3α5β2 AChRs were potently inhibited by mecamylamine as evidenced by the large reduction in opening frequency and shorter duration openings. Hexamethonium blocked α3β4 and α3α5β4 AChRs by reducing the channel open duration but did not reduce the channel open frequency. All traces were recorded at -80 mV. The block by both agents was reversible after 1 min washout. B, the relationship for reciprocal open time versus concentration of the blocking agent reveals their forward block rate constants. The relationship for hexamethonium block of α3β4 AChRs revealed a blocking rate of 1.2 × 10⁷ M⁻¹ s⁻¹. For mecamylamine block of α3β2 AChRs, the rate constant was 4.6 × 10⁷ M⁻¹ s⁻¹.