Fig. 1.
Estimation of maximal current through cyclic nucleotide-gated (CNG) channels in the whole cell configuration. Currents were triggered by wash in of cAMP following “break in” to whole cell configuration. The rate of cAMP wash in was assessed by monitoring activation of wild-type (WT) CNG channels (K1/2 = 40 μM). Wash in of 40 μM cAMP triggered a steady rise in current through CNG channels, reaching a plateau of 320 pA within 200 s. Subsequent exposure of the cell to 10 μM rolipram triggered an additional increase in current to a plateau of 590 pA. Based on the plateau current in the presence of rolipram and 40 μM cAMP in the patch pipette, we estimate the maximal current to be 1,080 pA (indicated level) and I/Imax-est to be 0.27.