The colonic H+,K+-ATPase functions as a Na+-dependent K+(NH4+)-ATPase in apical membranes from rat distal colon.
Recent studies have suggested that the colonic H+,K+-ATPase (HKalpha2) can secrete either Na+ or H+ in exchange for K+. If correct, this view would indicate that the transporter could function as either a Na+ or a H+ pump. To investigate this possibility a series of experiments was performed using apical membranes from rat colon which were enriched in colonic H+,K+-ATPase protein. An antibody specific for HKalpha2 was employed to determine whether HKalpha2 functions under physiological conditions as a Na+-dependent or Na+-independent K+-ATPase in this same membrane fraction. K+-ATPase activity was measured as [gamma-32P]ATP hydrolysis. The Na+-dependent K+-ATPase accounted for approximately 80% of overall K+-ATPase activity and was characterized by insensitivity to Sch-28080 but partial sensitivity to ouabain. The Na+-independent K+-ATPase activity was insensitive to both Sch-28080 and ouabain. Both types of K+-ATPase activity substituted NH4+ for K+ in a similar manner. Furthermore, our results demonstrate that when incubated with native distal colon membranes, the blocking antibody inhibited dramatically Na+-dependent K+-ATPase activity. Therefore, these data demonstrate that HKalpha2 can function in native distal colon apical membranes as a Na+-dependent K+-ATPase. Elucidation of the role of the pump as a transporter of Na+ versus H+ or NH4+ versus K+ in vivo will require additional studies.
Division of Renal Diseases and Hypertension Department of Internal Medicine, University of Texas, Houston Medical School, Houston, Texas 77030, USA.
J
J
Codina
T A
TA
Pressley
T D
TD
DuBose
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D001692:Biological Transport; D027682:Cation Transport Proteins; D002462:Cell Membrane / Q000201:enzymology; D003106:Colon / Q000201:enzymology*; D017506:H(+)-K(+)-Exchanging ATPase / Q000276:immunology / Q000378:metabolism*; D007093:Imidazoles / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000494:pharmacology
D000906:Antibodies; D027682:Cation Transport Proteins; D007093:Imidazoles; D000644:Quaternary Ammonium Compounds; C035235:Sch 28080; D010042:Ouabain; D000255:Adenosine Triphosphate; D012964:Sodium; D000251:Adenosine Triphosphatases; C022761:potassium transporting ATPase; C030149:sodium ammonium ATPase; D017506:H(+)-K(+)-Exchanging ATPase; D011188:Potassium