Ion transport systems in membrane vesicles isolated from crustacean tissues

Abstract Studies with membrane vesicles isolated from crustacean gill have offered evidence for three major transport systems believed to play central roles in ion transport across the gill epithelium. First, ATP‐dependent sodium/potassium and sodium/ammonium exchanges have been demonstrated in Na+ + K+ ‐ATPase‐rich membrane preparations, supporting the concept that ammonium ion can serve as an effective counterion for sodium transport from cytosol to blood. Second, an amiloride‐sensitive Na+ /H+ antiporter, demonstrated using a pH‐sensitive fluorescent dye, has been shown to be electrogenic, apparently exchanging 2 sodium ions for 1 hydrogen ion. These two transport systems, the first in the basolateral membrane and the second likely in the apical membrane, can achieve net transport of sodium ions from water to blood. Third, a Cl−/HCO3− exchanger has been demonstrated in membrane vesicles from crab gill, most likely playing a central role in the sodium‐independent transfer of chloride across the epithelium. Finally, although no direct studies of calcium transport in crab gill have been reported, indirect evidence from other tissues suggests that part of the calcium flux across the gill may be mediated by Ca2+ /H+ exchange. © 1993 Wiley‐Liss, Inc.