Ouabain-insensitive Na-ATPase activity in the basolateral membrane from rat jejunum.
1. In the basolateral membrane preparation of the rat enterocyte (jejunal tract) there is not only the well-known (Na,K)-ATPase activity, but also a ouabain-insensitive Na-ATPase. 2. The Na-ATPase is not activated by anions or other monovalent cations. As a substrate, ATP cannot be replaced by other nucleotides. 3. The Na-ATPase is insensitive to ouabain and bumetanide, inhibited partially by furosemide and totally by ethacrynate. 4. The activation of Na-ATPase at different Na concentrations shows an hyperbolic curve (Km = 15.7 +/- 2.3 mM and Vmax = 204 +/- 19 nmoles Pi/mg protein per min) different from the sigmoidal curve (Km = 9.8 +/- 1.2 mM and Vmax = 640 +/- 15 nmoles Pi/mg protein per min) shown by (Na,K)-ATPase. 5. These results are compared with the corresponding ones found in other animals and tissues in which the Na-ATPase was found. 6. The Na-ATPase activity can be interpreted as the enzymatic correspondent of a ouabain-insensitive Na pump, present in the basolateral membrane of the enterocyte different in behaviour with respect to the known Na pump.
Orsenigo
M N
MN
Dipartimento di Fisiologia e Biochimica Generali, Universita' di Milano, Italy.
Tosco
M
M
Esposito
G
G
Faelli
A
A
D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D002034:Bumetanide / Q000494:pharmacology; D027682:Cation Transport Proteins; D004976:Ethacrynic Acid / Q000494:pharmacology; D005665:Furosemide / Q000494:pharmacology; D007583:Jejunum / Q000166:cytology / Q000201:enzymology*; D008565:Membrane Proteins / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology*; D051381:Rats
D027682:Cation Transport Proteins; D008565:Membrane Proteins; D002034:Bumetanide; D010042:Ouabain; D005665:Furosemide; D000251:Adenosine Triphosphatases; C021838:sodium-translocating ATPase; D004976:Ethacrynic Acid