FIG. 3.

KB-R7943 reversibly blocks the lobster SGC channel recorded in outside-out configuration. A: outside-out patch recording from a cultured lobster ORN showing the inhibition of the lobster SGC channel activity by KB-R7943 in a concentration-dependent manner. The patch contained ≥11 SGC channels. Holding potential was −70 mV. The white dotted lines indicate the averaged current amplitude for each concentration of KB-R7943 tested for this particular example. The percentage of inhibition of the averaged current by KB-R7943 is shown above the dotted line. Current traces in higher time resolution allow observing single-channel currents in control condition and in presence of 50 μM of KB-R7943 (gray plots). Current traces and corresponding amplitude histogram provided on the right of the panel indicate a decrease in channel activity but not in single channel current amplitude (11.20 ± 0.18 pA, n = 12 in control and 11.32 ± 0.11 pA, n = 16 in presence of KB-R7943). B: I-V relationships of the SGC current recorded before, during, and after application of 50 μM KB-R7943. To generate I-V relationships, series of 150-ms ramp protocols from −120 to +100 mV were applied every 2 s. Two ramp currents are presented in the graph for each condition. The I-V relationships show the reversible blockage of the SGC current by KB-R7943. C: concentration dependence of KB-R7943 effects. Averaged steady-state currents were normalized to the averaged current in absence of KB-R7943 (holding potential: −70 mV). Data points represent means ± SE of n = 7–9 patches and were fit to a Hill equation providing an IC₅₀ of 13.82 μM and a Hill coefficient of 1.32. KB-R7943 blockage was reversible (n = 4; histogram). Mesylate (CH₃SO₃H, 200 μM) alone did not block the SGC channel (n = 5; histogram).