Abstract
Preparations of posterior gills isolated from postmoult shore crabs (Carcinus mediterraneus) that had been acclimated to dilute seawater were used for calcium‐transport studies. Gills were perfused and bathed with saline of identical composition, with ^45^Ca^2+^ ions added exclusively to the bathing solution or the perfusate for measurement of unidirectional influx or efflux, respectively. The unidirectional influx of calcium (5.57 ± 0.95 μmol h^−1^ per g gill fresh weight) significantly exceeded the efflux (3.15 ± 1.02 μmol h^−1^ per g gill fresh weight), indicating a net transgill influx of calcium.
Calcium influxes were inhibited when La^3+^ ions were added apically (IC~50~ = 7 × 10^−6^ mol 1^−1^) or basolaterally (IC~50~ = 1.6 × 10^−6^ mol 1^−1^). In addition, basolaterally applied La^3+^ ions inhibited effluxes with an IC~50~ of 3.0 × 10^−7^ mol 1^−1^. Amiloride had no significant effect on the unidirectional fluxes of calcium. Influxes of calcium gave a sigmoidal curve when plotted against the external concentration of calcium in the bath. The Hill coefficient (2.66 ± 0.20) suggested that there are at least two or three Ca^2+^ carrier systems that are active during the influxes of calcium. Moreover, apically added La^3+^ ions produced a concentration‐dependent inhibition of calcium influx, which is discussed in terms of inhibition of apically located calcium channels. By contrast, the inhibitory action of La^3+^ ions at the basolateral gill surfaces is discussed in terms of an effect on ATP‐dependent calcium transport and the Na^+^/Ca^2+^ exchanger. © 1994 Wiley‐Liss, Inc.