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 inside negative transepithelial potential difference (PD) was measured in perfused posterior gills of the euryhaline crab Pachygrapsus marmoratus acclimated to dilute sea water. The origin of the PD and the transport properties of the epithelium were investigated by ionic substitutions and by application of inhibitors. Diffusion of Na+ and Cl- ions at the apical side contributes to the establishment of the PD. Sodium cyanide (10(-2) M) added to the perfusion and incubation media almost completely 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 applied amiloride (10(-3) M) also reduced the Na+ influx by 27%. All inhibitions were concentration-dependent. From these results, it has been concluded that the transepithelial PD and Na+ influx are, at least partly, generated by active, metabolic energy-requiring processes. The effect of ouabain supports the existence of a Na+/K+ exchange mechanism linked to the presence of Na(+)-K+ ATPase in the basolateral membrane of posterior gills. The effect of amiloride is discussed.