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989180 
Journal Article 
Active ammonia absorption in the midgut of the Tobacco hornworm Manduca sexta L.: transport studies and mRNA expression analysis of a Rhesus-like ammonia transporter 
Weihrauch, D 
2006 
Yes 
Insect Biochemistry and Molecular Biology
ISSN: 0965-1748 
36 
10 
808-821 
English 
17027847 
WOS:000241912300007 
In this study the mid- and hindgut of Manduca sexta larvae were tested for their ammonia transport properties using a custom-made Ussing chamber. In the presence of 0.1 mmoll(-1) ammonia on both sides of the isolated epithelium, active transepithelial ammonia absorption (aTEPA) was observed in all midgut sections, with greatest transport rates (ca. 140 nmol cm(-2)h(-1)) detected in the median midgut. The hindgut showed no aTEPA. In the median midgut inhibition of energy metabolism by azide blocked aTEPA completely, whereas inhibition of vacuolar H(+)-ATPase by bafilomycin A(1) reduced the active transport by 50%. The imposition of a luminal-directed NH(3)-gradient (pH 6.5 apical, pH 8.5 basal) lowered the aTEPA by approximately 50% but did not reverse its direction. Apical addition of amiloride reduced aTEPA by 90%, suggesting a role of carrier-mediated ammonia transport across the apical membrane via a member of the NHE family. Inhibition of the microtubule network by colchicine reduced aTEPA by ca. 50%. In contrast, blocking basal K(+) channels by Ba(2+) had no effect on aTEPA. Using molecular methods, evidence for intestinal expression of a Rhesus-like ammonia transporter (RhMS) was found with low mRNA expression in midgut tissues, but high expression levels in the hindgut, Malpighian tublules and ganglia. 
Manduca sexta; active ammonia transport; rhesus-like protein; amiloride; bafilomycin A(1); colchicine; Ba2+; Ussing chamber