Expression and Function of a Novel Na-Cl Cotransporter Isoform in Zebrafish (Danio rerio)

Thiazide-sensitive Na-Cl cotransporter (NCC), SLC12A3, is a kidney-specific transporter in mammalian and is mainly expressed in the apical membrane of the distal convoluted tubule (DCT) cells. In mammalian DCT, NCC is responsible for co-transporting Na+ and Cl- from lumen into DCT cells, playing a major role in NaCl reabsorption. NCC also acts as the target for the thiazide diuretics, which is used to treat hypertension. However, only a few in vivo data were available to elucidate the transport mechanism of NCC. In the present study, zebrafish was used as an in vivo model to examine the role of NCC in Na+/Cl- uptake mechanisms. Two NCCs were cloned and sequenced. One (zNCCk) was mainly expressed in kidney and another (zNCCg, NCBI accessory number EF591989) was in gill. Real-time RT-PCR analysis indicated that mRNA expression of the zNCCg was induced by a high-Na+-low-Cl- environment. Incubating with metolazone, a specific inhibitor of NCC, was found to impair both Na+ and Cl- influx in 5-dpf zebrafish embryos. Knockdown of the zNCCg translation with specific morpholino caused a significant decrease in Cl- uptake of zebrafish embryos, while co-injection with the zNCCg capped mRNA completely rescued the defect in morphants. These results for the 1st time provide in vivo molecular physiological evidence for the involvement of the zNCCg in Cl- uptake mechanisms in zebrafish skin/gill.