Chloride transport in mitochondrion-rich cells of euryhaline tilapia (Oreochromis mossambicus) larvae

Horng JL, Hwang PP, Shih TH, Wen ZH, Lin CS, Lin LY. Chloride transport in mitochondrion-rich cells of euryhaline tilapia (Oreochromis mossambicus) larvae. Am J Physiol Cell Physiol 297: C845-C854, 2009. First published August 5, 2009; doi:10.1152/ajpcell.00218.2009.-A noninvasive 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 similar to 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 mu M ouabain or bumetanide inhibited the Cl- secretion by similar to 75%. In freshwater (FW)-acclimated larvae, a lower level of outward Cl- gradients (0.2 similar to 1 mM) was measured at the skin surface. Low-Cl- water (similar to 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) that express the NCC. An NCC inhibitor (100 mu M metolazone) reduced the flux by similar to 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.