Horng JL, Hwang PP, Shih TH, Wen ZH, Lin CS, Lin LY
Chloride Transport in Mitochondrion-Rich Cells of Euryhaline Tilapia (Oreochromis mossambicus) Larvae. [JOURNAL ARTICLE]
Am J Physiol Cell Physiol 2009 Aug 5.
A non-invasive scanning ion-selective electrode technique (SIET) was applied to measure Cl(-) transport at individual mitochondrion-rich cells (MRCs) in the skin of euryhaline tilapia (Oreochromis mossambicus) larvae. In seawater (SW)-acclimated larvae, outward Cl(-) gradients (20~80 mM higher than the background) were measured at the surface indicating a secretion of Cl(-) from the skin. By serial probing over the surface of MRCs and adjacent keratinocytes (KCs), a significant outward flux of Cl(-) was detected at the apical opening (membrane) of MRCs. Treatment with 100 microM ouabain or bumetanide inhibited the Cl(-) secretion by ~75%. In freshwater (FW)-acclimated larvae, a lower level of outward Cl(-) gradients (0.2~1 mM) was measured at the skin surface. Low-Cl(-) water (< 0.005 mM) acclimation increased the apical Na(+)-Cl(-) cotransporter (NCC) immunoreactivity of MRCs in the larval skin. An inward flux of Cl(-) was detected when probing the exterior surface of a group of MRCs (convex-MRCs) which express the NCC. An NCC inhibitor (100 microM metolazone) reduced the flux by ~90%. This study provides direct and convincing evidence for Cl(-) transport by MRCs of SW- and FW-acclimated euryhaline tilapia, and the involvement of an apical NCC in Cl(-) uptake of MRCs of FW-acclimated fish. Key words: Na+-Cl- cotransporter, osmoregulation, gills, ionoregulation.
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