Figure 2.

Estimation of the photoreleased concentration of 8-Br-cAMP. (A–C) Current responses in 0 Ca²⁺ Ringer solution (with 10 mM EGTA) induced by photorelease of 8-Br-cAMP as a function of flash intensity at −50 mV. In the absence of Ca²⁺ entry, the current was entirely due to CNG channels. (D–F) Ca²⁺ entry was also reduced by recording at +50 mV in Ringer solution. (A and D) Arrows indicate the time of application of light flashes of various relative intensities: 0.01, 0.1, 0.32, and 0.8 in A and 0.25, 0.4, 0.8, and 1 in D in two different neurons. Peak currents from the experiments in A and D were plotted as a function of the relative light intensity in B and E, respectively. The continuous line was the best fit of the Hill Eq. 1 to the data with the following values: (B) I_max = 1070 pA, F_1/2 = 0.28, n = 1.8; (E) I_max = 653 pA, F_1/2 = 0.34, n = 1.7. Collected results from data at −50 mV in 0 Ca²⁺ solution from three different olfactory sensory neurons (C), and from data at +50 mV in Ringer solution from two different olfactory sensory neurons (D). Each symbol represents a different cell. Both axes are normalized values. Normalized peak currents in each cell (I/I_max) were plotted versus the logarithm of the relative intensity normalized to the F_1/2 value (F/F_1/2) for each cell. The continuous line was the best fit of Eq. 1 to the collected data with n = 1.8 in C and 1.7 in F. The average value for n was 1.9 ± 0.4 (N = 3) at −50 mV and 0 Ca²⁺ solution, and 1.7 ± 0.1 (N = 2) at +50 mV in Ringer solution.