Figure 2.

Functional properties of CNG channels. (A) cGMP dose–response relationships from a representative patch for CNGA1 (■), CNGA1/CNGB1 (□), CNGA1/CNGB1Δ2–676 (●), CNGA1/CNGB1Δ2–701 (○), and CNGA1/CNGB1ΔCaM (▴). Currents were measured at 60 mV, normalized to the maximum value in saturating cGMP (2.5 mM), and superimposed with the Hill equation, I/I_max = 1/(1+ (K_1/2/[cGMP])ⁿ), with K_1/2 = 55 μM and n = 2.5. (B) Fractional activation of CNG channels by cAMP, a partial agonist. Each channel construct is depicted by the same symbol as in A, except for Ca²⁺/CaM with CNGA1/CNGB1 (bowties). Values were determined by normalizing the current at 60 mV in saturating (16 mM) cAMP (or saturating cAMP with Ca²⁺/CaM) to that in saturating (2.5 mM) cGMP. Error bars represent the SEM; those not visible are within the symbols. n is ≥ 3 for each point.