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. 2001 Nov 1;118(5):523–546. doi: 10.1085/jgp.118.5.523

Figure 4.

Figure 4

Chimeric CNG channel subunit X-α containing BD from the α subunit fCNG2 is less efficiently activated by cAMP than is X-β. (A) Schematic shows sequence of X-α is identical to that of X-β except that the BD sequence is that of fCNG2. (top traces) Macroscopic current traces from homomeric X-α channels elicited by the indicated concentrations of cAMP. (bottom traces) Currents during voltage steps at indicated steady-state cAMP concentrations (tested as in Fig. 1). (B1–B4) Excerpts of single X-α channel recordings at indicated potentials and steady-state cAMP concentrations (collected as in Fig. 2). Popen values from the excerpt in B4 (30 mM cAMP) are 0.778 at +80 mV and 0.646 at −80 mV. (C) Dose–response data (closed circles) for X-α activation by cAMP at −100 mV, from the patch shown in A. Solid line shows Hill equation fit with K1/2 = 717 ± 47 μM, h = 1.241 ± 0.051, and the graph is normalized with Pmax,cAMP at cAMP set to be 0.49, the mean from single-channel measurements. For comparison, the dashed line shows cAMP dose–response curve for X-β, taken from Fig. 1 C and normalized using the Pmax,cAMP of 0.98 derived from single-channel measurements.