Fig. 4.

Effects of PTX on muscarine-mediated inhibition of ACh release and on Ca²⁺ currents. A, Percentage of inhibition of ACh release at four pulse amplitudes by different muscarine concentrations: 10 μm, ▪; 20 μm, ■; 50 μm, ▾; 70 μm, ○. B, Effect of PTX on DI curves at different pulse amplitudes (the same data as in A). AverageK_i values (n = 6) for the four pulse amplitudes are given in Table 1. C, Effect of PTX B subunit on DI curves at different pulse amplitudes: −0.6 μA, ▪; −0.9 μA, ●; −1.2 μA, ■; −1.5 μA, ○. Average K_i values (n = 4) for the four pulse amplitudes are given in Table 1. The curves inB and C were fitted by the sigmoidal dose–response (variable slope) equation by Graph PadPrism software (R² > 0.9). D, A 100 μm concentration of muscarine had no effect on Ca²⁺ currents at PTX-treated preparation. Control (solid line); after addition of 100 μmmuscarine (stippled line) (average of 200 traces).