Evidence that odor-induced background currents are mediated by CNG channel activation
| Odor-induced background current | CNG channel current activated by 8-Br-cGMP | |
|---|---|---|
| Amplitude (pA) | −1.7 ± 0.6 | −1.2 ± 0.5 |
| (1 mm external Ca2+) | (n = 10) | (n = 3) |
| Reversal potential (mV) | −27.4 ± 9.5 | −29.0 ± 3.6 |
| (1 mm external Ca2+) | (n = 10) | (n = 3) |
| Amplitude (pA) | −19.5 ± 8.4 | −15.0 ± 4.5 |
| (external Ca2+reduced) | (n = 3) | (n = 3) |
| Reversal potential (mV) | +7.6 ± 12.1 | −3.8 ± 8.1 |
| (external Ca2+reduced) | (n = 3) | (n = 3) |
| Cd2+ (3 mm) | Complete block | Complete block |
| LY83583 (20 μm) | Complete block | Complete block |
| W-7 (100 μm) | Complete block | Complete block |
Currents through CNG channels were measured with the use of the perforated patch-clamp technique as described previously (Leinders-Zufall et al., 1995a, 1996). A concentration of 1 μm 8-Br-cGMP was used in these experiments because this cGMP level can be produced by physiological concentrations of CO (Leinders-Zufall et al., 1995a). For the analysis of the effect of low external Ca2+ (0.6 μm) on established odor-induced background currents, cells were first exposed to normal 1 mm external Ca2+ and stimulated with an odor pulse as shown in Figure 2B. After the background current was fully activated, rapid switching to low Ca2+ solution was performed. The shift in reversal potential under low Ca2+ presumably reflects a contribution of secondary, Ca2+-dependent conductances to the net inward currents observed here.