AJP - Regulatory, Integrative and Comparative Physiology, Vol 241, Issue 5 370-R378, Copyright © 1981 by American Physiological Society
Amiloride-sensitive ammonium and sodium ion transport in the blue crab
T. A. Pressley, J. S. Graves and A. R. Krall
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.
