Fig. 4.

Functional characteristics of SthK in inside-out patches. (A) (Left) Current–voltage relationship as measured under four different ionic conditions. Bath solution and pipette solution contained either K⁺ or Na⁺ ions, respectively. The bath solution additionally contained a saturating cAMP concentration of 500 µM. Positive values indicate outward currents, and negative values indicate inward currents. Current amplitudes are normalized to the maximum value obtained at +100 mV at K_int/K_ex and K_int/Na_ex, respectively. Means were calculated from three to nine patches. Error bars indicate SEM. (Right) Representative currents (black traces: at 500 µM cAMP; gray traces: no cAMP) for each of the four ionic conditions. (B) Single-channel events were recorded at a saturating concentration of 500 µM cAMP at symmetrical potassium and +100 mV. (Left) Representative current–amplitude histogram for a three-channel patch. The main histogram was fitted by the sum of three Gaussian functions (for one closed and two open levels) (black line). The amplitude of the single-channel current was determined to be 8.1 pA (with a SD obtained from the Gaussian fit of 0.02 pA). The Inset shows the same histogram at higher magnification to visualize the third open level peak. This histogram was fitted by the sum of two Gaussian functions (black line). (Right) Shown are representative traces from the same recording as shown in the left panel. Closed and open levels are indicated as dashed (c) and dotted lines (o).