SN 6 is a selective Na ⁺ /Ca ²⁺ exchanger inhibitor, which inhibits the initial rate of ⁴⁵ Ca ²⁺ uptake into NCX1, NCX2, and NCX3 transfectants with IC ₅₀ values of 2.9 ± 0.12, 16 ± 1.1, and 8.6 ± 0.27 μM. SN 6 (up to 30 μM) also less potently inhibits muscarinic acetylcholine receptor, with a higher IC ₅₀ of 18 μM. SN 6 (0.3-30 μM) completely inhibits the initial rate of Na ⁺ _i -dependent ⁴⁵ Ca ²⁺ uptake into Na ⁺ -loaded sarcolemmal vesicles in a dose dependent manner (IC ₅₀ , 5.3 ± 0.37 μM). SN 6 (0.3-10 μM) dose-dependently protects against the hypoxia/reoxygenation-induced LDH release in parental LLC-PK1 cells and NCX1 transfectants but not in K229Q transfectants. SN 6 (1-30 μM) suppresses the bidirectional outward and inward I _NCX in a concentration-dependent manner, with IC ₅₀ values of 2.3 μM and 1.9 μM, respectively. SN 6 also inhibits bidirectional current (I _NCX ) in a [Na ⁺ ]i concentration-dependent manner, with IC ₅₀ values of 3.4 μM, 2.3 μM, and 1.1 μM at 10 mM, 20 mM, and 30 mM [Na ⁺ ]i, respectively. SN 6 inhibits hypoxia/reoxygenation-induced LDH release with an IC ₅₀ value of 0.63 ± 0.15 μM in NCX1 transfectants.