Ion transport across the skin of the mudskipper Periophthalmus modestus

Abstract

An amphibious teleost, the mudskipper ( Periophthalmus modestus), showed a serosa-positive transepithelial potential difference (PD) across the skin isolated from several areas of the body. However, the highest PD was observed in skins isolated from the pectoral fin. In skin isolated from the pectoral fin of mudskipper, the PD was due to active Cl − secretion, because net 36Cl − flux was identical with the simultaneously measured short-circuit current ( I sc). No net Na + flux was observed under the short-circuited condition. The I sc in skins isolated from pectoral fin was diminished by omitting Cl − or Na + bilaterally from the bathing media. The I sc was also diminished by serosal ouabain, a specific blocker of Na + K + -ATPase , and by serosal bumetanide, a specific inhibitor of the Na +-K +-Cl − cotransporter. K + channel blockers, Ba 2+ and Cs +, applied to the serosal surface and the Cl − channel blocker, diphenylamine-2-carboxilic acid, applied to the apical membrane reduced I sc and increased tissue resistance, R t. The Na + channel blocker, amiloride, had no effect on either I sc or R t. From these data we proposed a current model for ion transport across the skin of the mudskipper; Na + K + -ATPase , Na +-K +-Cl − cotransporter and K + channels are localized to the basolateral membrane and CI channels are located in the apical membrane of the epithelium. A morphological study demonstrated that skins isolated from the pectoral fin contained a large number of mitochondrion-rich cells (MRC) and many pits on the surface. Beneath the pits, relatively large cells were observed on light micrograph, which contained many cytoplasmic granules, presumably mitochondria. A good correlation was obtained between the area occupied by the MRC and the I sc. These characteristics were similar to those of the operculum, which is considered as a model for gills in seawater teleosts but different from those of frog skins.