Table 1.

Evidence that odor-induced background currents are mediated by CNG channel activation

Odor-induced background currentCNG 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 blockComplete block
LY83583 (20 μm)Complete blockComplete block
W-7 (100 μm)Complete blockComplete 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.