Response of Na(+)-dependent ATPase activities to the contaminant ammonia nitrogen in Tapes philippinarum: possible atpase involvement in ammonium transport.
In vivo and in vitro experiments elicited different responses to ammonia nitrogen (ammonia-N) of gill and mantle Na,K-ATPase and ouabain-insensitive Na-ATPase activities in the Philippine clam Tapes philippinarum. Short-term (120 h) exposed clams to sublethal ammonia-N (NH(3)+NH (4) (+) ) concentrations (1.5 and 3.0 mg/L ammonia-N) showed enhanced gill and mantle ouabain-insensitive ATPase activity and decreased mantle Na,K-ATPase activity with respect to unexposed clams, while gill Na,K-ATPase was unaffected. In vitro experiments showed that NH (4) (+) could efficiently replace Na(+) in ouabain-insensitive ATPase activation and K(+), but not Na(+), in Na, K-ATPase activation. Simple saturation kinetics was constantly followed with similar K (0.5) values to that of the substituted cation. The same maximal ouabain-insensitive ATPase activation was obtained at 80 mM Na(+) or NH (4) (+) in the gills and at 50 mM Na(+) or NH (4) (+ ) in the mantle and that of Na,K-ATPase at 10 mM K(+) or NH (4) (+) in the presence of 100 mM Na(+) in both tissues. The two coexistent ATPase activities maintained their typical response to ouabain also when stimulated by NH (4) (+) : when activated by Na(+)+K(+) or by Na(+)+NH (4) (+) the ATPase activity was completely suppressed by 10(-3 )M ouabain, whereas the Na(+)- or NH (4) (+) -stimulated ATPase activity was unaffected by up to 10(-2 )M ouabain. The whole of the data suggests a possible involvement of the two ATPase activities in NH (4) (+) transmembrane transport.
Pagliarani
Alessandra
A
Department of Biochemistry G. Moruzzi, Section of Veterinary Biochemistry, University of Bologna, Via Tolara di Sopra, 50, 40064, Ozzano Emilia, BO, Italy. alessandr.pagliarani@unibo.it
Bandiera
Patrizia
P
Ventrella
Vittoria
V
Trombetti
Fabiana
F
Manuzzi
Maria Pia
MP
Pirini
Maurizio
M
Borgatti
Anna Rosa
AR
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000641:Ammonia / Q000633:toxicity*; D000818:Animals; D049872:Bivalvia / Q000187:drug effects* / Q000201:enzymology; D027682:Cation Transport Proteins / Q000378:metabolism*; D005880:Gills / Q000187:drug effects / Q000201:enzymology; D008861:Microsomes / Q000187:drug effects / Q000201:enzymology; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014874:Water Pollutants, Chemical / Q000633:toxicity*
D027682:Cation Transport Proteins; D000644:Quaternary Ammonium Compounds; D014874:Water Pollutants, Chemical; D000641:Ammonia; D000251:Adenosine Triphosphatases; C021838:sodium-translocating ATPase; D000254:Sodium-Potassium-Exchanging ATPase