Do amiloride and ouabain affect ammonia fluxes in perfused Carcinus gill epithelia?

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Abstract
The effects of inhibitors on the efflux of ammonia (from the basolateral to the apical side, Jb→a) were studied in preparation of isolated Carcinus gills immersed in dilute seawater (DSW) that was identical to the perfusion solution. Adding 10−4M amiloride to the solution bathing the gill preparations reduces the efflux of ammonia by 29% relative to the control value. Under experimental conditions, it appears that only about 1% of the amiloride-sensitive influx of Na+ (Ja→b) can be exchanged with NH on an equimolar basis. The ammonium ion is apparently transported at the basolateral side by a carrier-mediated process. Kinetic analyses of the influx of ammonium ions revealed a Km of 36.99 μM and a maximum velocity (Vmax) equal to 19.6 μmol g−1 h−1. Basolaterally applied ouabain (5 × 10−3M) and NaCN (10−3M) reduced the efflux of ammonia by 46.7 and 42.2%, respectively, suggesting an interaction of NH with the basolaterally located Na+/K+ exchanger in which NH appears to be able to substitute for K+.

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