Figure 1.

M₁ receptor-mediated inhibition of the K_ATP current. Chart recordings of whole-cell current recorded in the COS7 cell cotransfected with Kir6.2, SUR2A, and M₁ receptor cDNA. The current deflections are the results of ramp pulses. (A) The perfusion of 100 μM pinacidil started at the time indicated by the arrow (↑) under the current trace. The applications of ACh and 10 μM glibenclamide are indicated by the horizontal lines above the trace. (B) The whole-cell K_ATP current recorded in the COS7 cell that was not cotransfected with the M₁ receptor. The perfusion of 100 μM pinacidil started at the time indicated by ↑ and finished at ↓ under the trace. (C) Spontaneous activation of the K_ATP current after the formation of the whole-cell patch using the pipette solution containing 10 μM ATP. (D) I–V relationships obtained at the times indicated by i–vi in A. The reversal potential was ≈−85 mV. (E) Concentration-inhibition relationship for ACh. The percent inhibition was plotted against ACh concentration. The following Hill equation is fitted to each data point: % inhibition = 100/{1 + (IC₅₀/[ACh])^n_H}, where IC₅₀ is the concentration for the half-maximal inhibition, and n_H is the Hill coefficient. IC₅₀ = 0.54 ± 0.12 μM, and n_H = 0.98 ± 0.22 (n = 6). The line was drawn with these values.