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(-4) M 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 NH4+ 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 microM and a maximum velocity (Vmax) equal to 19.6 mumol g-1.h-1. Basolaterally applied ouabain (5 x 10(-3) M) and NaCN (10(-3) M) reduced the efflux of ammonia by 46.7 and 42.2%, respectively, suggesting an interaction of NH4+ with the basolaterally located Na+/K+ exchanger in which NH4+ appears to be able to substitute for K+.
Lucu
C
C
Center for Marine Research Rovinj, Institute Ruder Bosković, Rovinj, Yugoslavia.
Devescovi
M
M
Siebers
D
D
D000584:Amiloride / Q000494:pharmacology*; D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D003386:Brachyura / Q000378:metabolism*; D005880:Gills / Q000187:drug effects* / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology*; D012623:Seawater
D010042:Ouabain; D000641:Ammonia; D000584:Amiloride