Figure 5. The mutually occlusive effects of ATP (6 μm) and cytisine (60 μm) at the single channel level.

Note that shortly after application of ATP, multiple ATP-gated channels are opened and saturation of the amplifier is observed. After the cessation of superfusion with ATP, discrete openings characteristic of ATP are observed as the extracellular concentration of ATP declines. In B, application of cytisine opens nicotinic receptor-gated ion channels in the same patch. As above, saturation of the patch clamp amplifier occurred with the opening of two or more nicotinic receptors. In C, the combination of ATP (6 μm) + cytisine (60 μm) reveals mutual occlusion of the discrete channel openings. The effect was reversible (data not shown). The excised patch was made from the same cell as in Fig. 5 using the same concentrations of agonists and the same holding potential (-110 mV). For further details, see text.