Figure 2.

Thio-phosphorylation of rod CNG channels prevents Ca²⁺/CaM inhibition. A, Excised patches containing rod CNG channels were incubated with 250 μm Mg²⁺ ATP-γ-S for 5 min. The patch was then washed free of ATP-γ-S, and cGMP dose-response curves were obtained at 30 sec and 5 min after treatment. Note that ATP-γ-S prevents the spontaneous increase in cGMP sensitivity that occurs after excision (see Fig. 1 A), indicating that the CNG channels are persistently thio-phosphorylated. B, cGMP dose-response curves obtained before (triangles) and during (circles) application of Ca²⁺/CaM. Note that thio-phosphorylation prevents Ca²⁺/CaM inhibition.