– NS8593 hydrochloride is a potent and selective small conductance Ca2+-activated K+ channels (SK channels) inhibitor. NS8593 hydrochloride reversibly inhibits SK3-mediated currents with a Kd value of 77 nM. NS8593 hydrochloride inhibits all the SK1-3 subtypes Ca2+-dependently (Kds of 0.42, 0.60, and 0.73 ?M, respectively, at 0.5 ?M Ca2+), and does not affect the Ca2+-activated K+ channels of intermediate and large conductance (hIK and hBK channels, respectively).