EFFECTS OF IONS SUBSTITUTIONS AND OF INHIBITORS ON TRANSEPITHELIAL POTENTIAL DIFFERENCE AND SODIUM FLUXES IN PERFUSED GILLS OF THE CRAB PACHYGRAPSUS-MARMORATUS

With the same saline on both sides of the epithelium, a spontaneous in side negative transepithelial potential difference (PD) was measured i n perfused posterior gills of the euryhaline crab Pachygrapsus marmora tus acclimated to dilute sea water. The origin of the PD and the trans port properties of the epithelium were investigated by ionic substitut ions and by application of inhibitors. Diffusion of Na+ and Cl- ions a t the apical side contributes to the establishment of the PD. Sodium c yanide (10(-2) M) added to the perfusion and incubation media almost c ompletely inhibited the transepithelial PD and considerably decreased the Na+ influx. Internally perfused ouabain (5.10(-3) M) halved the PD and the Na+ influx but had no effect on the Na+ efflux. Externally ap plied amiloride (10(-3) M) also reduced the Na+ influx by 27%. All inh ibitions were concentration-dependent. From these results, it has been concluded that the transepithelial PD and Na+ influx are, at least pa rtly, generated by active, metabolic energy-requiring processes. The e ffect of ouabain supports the existence of a Na+/K+ exchange mechanism linked to the presence of Na+-K+ ATPase in the basolateral membrane o f posterior gills. The effect of amiloride is discussed.