title: Amiloride-sensitive ammonium and sodium ion transport in the blue crab.
abstract: In the estuarine crab, Callinectes sapidus, net NH4+ efflux was twice as high in animals acclimated to 17% salinity seawater (SW) (0.495 +/- 0.084 mumol . h-1 . g wet wt-1, n = 7) than in animals acclimated to full-strength 35% SW (0.212 +/- 0.028 mumol . h-1 . g-1, n = 7). Amiloride (3 X 10(-4) M) in the external SW reversibly inhibited these effluxes by 63 +/- 6% (n = 6) and 67 +/- 6% (n = 5), respectively. Unidirectional Na+ influx was reversibly inhibited 42 +/- 6% (n = 7) by amiloride in 17% SW-acclimated crabs and 49 +/- 7% (n = 8) in 35% SW-acclimated crabs. This mutual sensitivity to amiloride is evidence for a Na+/NH4+ exchanger. Inhibition of unidirectional Na+ efflux by Na+-free SW indicates the presence of an obligate Na+/Na+ exchange component that accounts for at least 42% of the Na+ flux and is also amiloride sensitive. The lack of inhibition by amiloride of the net H+ efflux does not support the presence of a Na+/H+ exchanger. Acclimation of the crab to dilute SW may involve an increase in the activity of the Na+/NH4+ exchanger in the gills, but this mechanism contributes only a small fraction of the total Na+ transport.
mesh_terms: D000064:Acclimatization; D000584:Amiloride / Q000494:pharmacology*; D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D003386:Brachyura / Q000378:metabolism*; D005880:Gills / Q000378:metabolism; D007700:Kinetics; D010101:Oxygen Consumption / Q000187:drug effects; D011719:Pyrazines / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism*
chemical_list: D011719:Pyrazines; D000641:Ammonia; D000584:Amiloride; D012964:Sodium