SN 6 (SN6) is a selective Na+/Ca2+ exchanger (NCX) inhibitor (IC50s of NCX1: 2.9 μM , NCX2: 16 μM ,NCX3: 8.6 μM)

NCX3:8.6 μM, NCX1:2.9μM , NCX2:16μM

SN-6 [2-[4-(4-nitrobenzyloxy)benzyl]thiazolidine-4-carboxylic acid ethyl ester], a newly synthesized and selective Na(+)/Ca(2+) exchange (NCX) inhibitor. SN-6 (0.3-30 microM) inhibited preferentially intracellular Na(+)-dependent (45)Ca(2+) uptake (i.e., the reverse mode) compared with extracellular Na(+)-dependent (45)Ca(2+) efflux (i.e., the forward mode) in NCX1-transfected fibroblasts. SN-6 was 3- to 5-fold more inhibitory to (45)Ca(2+) uptake in NCX1 (IC(50) = 2.9 microM) than to that in NCX2 or NCX3. SN-6 at lower doses (IC(50) = 0.63 microM) potently protected against hypoxia/reoxygenation-induced cell damage in renal tubular cells overexpressing NCX1, suggesting that this drug predominantly works under hypoxic/ischemic conditions. These properties of SN-6, which may be derived from its interaction with the XIP region, are advantageous to developing it as a new anti-ischemic drug.

Confluent transfectants in 24-well dishes were loaded with Na+ by incubation at 37°C for 40 min in 0.5 ml of balanced salt solution (BSS) (10 mM HEPES/Tris, pH 7.4, 146 mM NaCl, 4 mM KCl, 2 mM MgCl2, 0.1 mM CaCl2, 10 mM glucose, and 0.1% bovine serum albumin) containing 1 mM ouabain and 10 mM monensin. 45Ca2+ uptake was then initiated by switching the medium to Na+ -free BSS (replacing NaCl with equimolar choline chloride) or to normal BSS, both of which contained 0.1 mM 45CaCl2 (370 kBq/ml) and 1 mM ouabain. After a 30-s incubation, 45Ca2+ uptake was terminated by washing cells four times with an ice-cold solution containing 10 mM HEPES/Tris, pH 7.4, 120 mM choline chloride,and 10 mM LaCl3. Cells were then solubilized with 0.1 N NaOH, and aliquots were taken for determination of radioactivity and protein. When present, SN-6 and KB-R7943 were included in the medium 15 min before the start of 45Ca2+ uptake