Figure 2. Phenylurea is a weak SK2 channel modulator.

(a) Raw current traces from an inside-out patch with SK2-a channels expressed. The SK2 channels are activated by 200 nM Ca²⁺, with subsequent potentiation by PHU at the concentrations indicated (all in the presence of 200 nM Ca²⁺). A voltage ramp, from −100 mV to +100 mV, was applied. (b) Dose-response curves for PHU (n = 4) and 1-EBIO (n = 5) for their potentiation of the SK2 channel activities (all in the presence of 200 nM Ca²⁺). The current amplitudes were measured at −90 mV and normalized to the maximal current obtained either with PHU or 1-EBIO. (c) EC50s of potentiation of the SK2 channel activities by PHU (n = 4), 1-EBIO (n = 5), DCEBIO (n = 8), CyPPA (n = 6) and NS309 (n = 3). All modulators were in a 200 nM Ca²⁺ solution. Note that the y-axis is in the log scale. (d) SK2-a (n = 3) and SK2-b (n = 6) have the same responses to application of NS309. Because SK2-b is less sensitive to Ca²⁺ for its activation, 500 nM Ca²⁺ was used instead of 200 nM Ca²⁺ for SK2-a channels. All data are mean ± s.e.m.