Figure 4.

Dependence of open times on [cGMP]. All data were filtered at 2 kHz. (A) Fast open time τ_o1 and slow open time τ_o2 of single cGMP-gated channels as function of [cGMP]. Kinetic constants were measured at 7, 20, 70, and 700 μM cGMP and at −50 and +50 mV. Parentheses indicate values at 7 and 70 μM, respectively. 16–63 traces of 500-ms duration were analyzed. When switching from −50 to +50 mV, both τ_o1 and τ_o2 increased at 70 μM cGMP and even more so at 700 μM cGMP, whereas at 7 and 20 μM cGMP, no statistically significant increase of either τ_o1 and τ_o2 was observed. (B) Voltage-dependent incidence of the relative contribution of fast and slow exponential in the open-time histograms as function of [cGMP]. Plotted is the ratio A_n (+50 mV)/A_n (−50 mV). At low [cGMP], A₂ (+50 mV)/A₂ (−50 mV) is larger than A₁ (+50 mV)/A₁ (−50 mV), suggesting that the contribution of the slow exponential is more influenced by voltage than that of the fast exponential.