Y-33075 dihydrochloride is a selective ROCK inhibitor with an IC₅₀ of 3.6 nM. IC50 & Target: IC50: 3.6 nM (ROCK), 420 nM (PKC), 810 nM (CaMKII)^[1] In Vitro: Y-33075 (Y-39983) is a potent ROCK inhibitor, with an IC₅₀ of 3.6 nM. Y-33075 also inhibits PKC and CaMKII more potently than Y-27632, and the IC₅₀s of Y-27632 and Y-33075 for PKC are 9.0 μM and 0.42 μM, respectively, whereas the IC₅₀s of Y-27632 and Y-33075 for CaMKII are 26 μM and 0.81 μM, respectively. The IC₅₀s of Y-27632 and Y-33075 for PKC is 82 and 117 times those for ROCK, respectively, whereas the IC₅₀s of Y-27632 and Y-33075 for CaMKII is 236 and 225 times those for ROCK, respectively^[1]. Y-33075 (Y-39983, 10 μM) extends neurites in the retinal ganglion cells (RGCs) compared with those in RGCs treated without Y-39983^[2]. Y-33075 (Y-39983, 1 μM) inhibits the contraction of rabbit ciliary artery segments evoked by histamine in Ca²⁺-free solutions. Y-33075 (10 μM) shows no effect on the [Ca²⁺]i increase with the high-potassium (high-K) solution^[3]. In Vivo: In rabbits, Y-39983 (≥0.01%) significantly lowers intraocular pressure (IOP) at 2 hours after topical administration. In monkeys, Y-39983 (0.05%)-treated eyes show significant reduction of IOP between 2 and 7 hours after topical administration^[1]. Y-39983 (100 μM) increases the regenerating axons of retinal ganglion cells (RGCs) in the eyes of the rats^[2].