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In the present article we review our findings on split lamella preparations of crab gills mounted in modified Ussing-chambers with respect to mechanistic and ecophysiological aspects. The leaky gill epithelium of shore crabs adapted to brackish water absorbs Na + and C1-in a coupled mode, and shows similarities to other salt-absorbing epithelia exposed to moderately diluted media. The results so far obtained for NaCI uptake across the gills of the shore crab are compatible with a transport model where two cell types operate in parallel, one displaying cotransport-like NaC1 absorption, similar to that in the thick ascending limb of Henle's loop of the mammalian mephron, and the other one with characteristics of amiloride-sensitive, channel-mediated Na + uptake by frog skin. Although there is no clear evidence for the apical mechanisms in this model, it may serve as a good basis for more detailed studies in the future. The moderately tight gill epithelium of freshwater adapted Chinese crabs absorbs Na + and C1-independently from each other, and shows similarities to other salt-absorbing epithelia exposed to freshwater. The characteristics of a positive, Na +-dependent short-circuit current with externally C1--free saline indicate that active Na + uptake proceeds in a frog-skin-like mode via apical Na+-channels and the basolateral Na+/K+opump. The nature of a negative short-circuit current with external C1--saline indicates that active and Na +-independent CI-uptake is driven by an apical V-type H~--pump and proceeds via apical C1-/ HCO3--exchange and basolateral C1--channels.

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