SKA-31 (Naphtho[1,2-d]thiazol-2-ylamine) is an activator of KCa3.1 and KCa2 channels (EC50s: 260, 2900, 2900 nM for KCa3.1, KCa2.1 and KCa2.2 respectively).

SKA-31 activates KCa2.1 with EC(50) values of 2.9 microM, KCa2.2 with an EC(50) value of 1.9 microM, KCa2.3 with EC(50) values of 2.9 microM, and KCa3.1 with EC(50) values of 260 nM. SKA-31 activated native KCa2.3 and KCa3.1 channels in murine endothelial cells [1]. SKA-31 (1 μM) activated KCa3.1 and KCa2.3 channels and induced membrane hyperpolarization in CAEC of wt (ΔMP -45 mV). SKA-31 (200 nM, 500 nM) significantly enhanced EDHF vasodilations in wt [2].

Administration of 10 and 30 mg/kg SKA-31 lowered mean arterial blood pressure by 4 and 6 mm Hg in normotensive mice and by 12 mm Hg in angiotensin-II-induced hypertension [2]. SKA-31 (10 μM) inhibited myogenic tone by 80% in cremaster and ～65% in middle cerebral arteries, with IC50 values of ～2 μM in both vessels [3].

Jurkat E61 and MEL cells were seeded at 10^5 cells/ml in 12-well plates. SKA-31 was added at concentrations of 10 and 100 μM in a final DMSO concentration of 0.1%, which was found not to affect cell viability. After 48 h, the cells in each well were well mixed and resuspended, and the number of trypan blue-positive cells in three aliquots from each well was determined under a light microscope. The test was repeated twice [1].

For intravenous injection, SKA-31 was dissolved at 10 mg/ml in a mixture of 10% Cremophor EL and 90% saline and injected at 10 mg/kg. For intraperitoneal application, SKA-31 was dissolved at 10 mg/ml in Miglyol 812 neutral oil (caprylic/capric triglyceride). After tail vein injection of the aqueous solution or intraperitoneal administration of the oily solution, approximately 200 μl of blood was collected from the tail into EDTA blood sample collection tubes at various time points. For very early time points (3, 5, and 10 min) after intravenous administration, blood samples were obtained by cardiac puncture under deep isoflurane anesthesia. Plasma was separated by centrifugation and stored at -80°C pending analysis. After determining that SKA-31 plasma concentrations peaked 2 h after application (10 mg/kg i.p.), we took blood samples under deep isoflurane anesthesia by cardiac puncture from a group of three rats before sacrificing the animals to remove brain, heart, liver, spleen, and fat. Tissue samples were homogenized in 1 ml of H2O with a homogenizer, and the protein was precipitated with 1 ml of acetonitrile. The samples were then centrifuged at 3000 rpm, and supernatants were concentrated to 1 ml. Plasma and homogenized tissue samples were purified using C18 solid-phase extraction cartridges. Elution fractions corresponding to SKA-31 were evaporated to dryness under nitrogen and dissolved in acetonitrile [1].