NS 8593 is an inhibitory gating modifier of small-conductance calcium-activated potassium (KCa2/SK) channels (Kds = 0.42, 0.6, and 0.73 μM for KCa2.1/SK1, KCa2.2/SK2, and KCa2.3/SK3, respectively, in the presence of calcium) that decreases the calcium sensitivity of SK channels. It is selective for KCa2/SK channels over intermediate- (KCa3.1/IKCa1) and large-conductance (BK) potassium channels at 10 μM. NS 8593 induces relaxation of potassium- or acetylcholine chloride-precontracted isolated tracheal rings from wild-type mice (IC50s = 8.9 and 39.8 μM, respectively) or from mice in an ovalbumin-induced model of allergic asthma (IC50s = 16.4 and 32.2 μM, respectively). It inhibits aerosolized acetylcholine chloride-induced increases in respiratory system resistance in mice when administered as an aerosol at a dose of 500 μM. NS 8593 (5 mg/kg) decreases the duration of burst-pacing-induced atrial fibrillation in normotensive and spontaneously hypertensive rats.
