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

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 4+ 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 4+ with the basolaterally located Na+/K+ exchanger in which NH 4+ appears to be able to substitute for K+.