ML133 hydrochloride is a selective Kir2 family channels inhibitor, with an IC50 of 1.8 μM at pH 7.4 and 290 nM at pH 8.5[1].
ML133, which inhibits Kir2.1 with IC50 of 1.8 μM at pH 7.4 and 290 nM at pH 8.5, but exhibits little selectivity against other members of Kir2.x family channels[1].ML133 has no effect on Kir1.1 (IC50 > 300 μM), and displays weak activity for Kir4.1 (76 μM) and Kir7.1 (33 μM), making ML133 the most selective small molecule inhibitor of the Kir family reported to date[1].
References:
[1]. Wang HR, et al. Selective inhibition of the K(ir)2 family of inward rectifier potassium channels by a small molecule probe: the discovery, SAR, and pharmacological characterization of ML133. ACS Chem Biol. 2011 Aug 19;6(8):845-56.