P-type ATPases require both - and -subunits for functional activity. Although an -subunit for colonic apical membrane H-K-ATPase (HKc) has been identified and studied, its -subunit has not been identified. We cloned putative -subunit rat colonic H-K-ATPase (HKc) cDNA that encodes a 279-amino-acid protein with a single transmembrane domain and sequence homology to other rat -subunits. Northern blot analysis demonstrates that this HKc is expressed in several rat tissues, including distal and proximal colon, and is highly expressed in testis and lung. HKc mRNA abundance is upregulated threefold compared with normal in distal colon but not proximal colon, testis, or lung of K-depleted rats. In contrast, Na-K-ATPase ₁ mRNA abundance is unaltered in distal colon of K-depleted rats. Na depletion, which also stimulates active K absorption in distal colon, does not increase HKc mRNA abundance. Western blot analyses using a polyclonal antibody raised to a glutathione S-transferase-HKc fusion protein established expression of a 45-kDa HKc protein in both apical and basolateral membranes of rat distal colon, but K depletion increased HKc protein expression only in apical membranes. Physical association between HKc and HKc proteins was demonstrated by Western blot analysis performed with HKc antibody on immunoprecipitate of apical membranes of rat distal colon and HKc antibody. Tissue-specific upregulation of this -subunit mRNA in response to K depletion, localization of its protein, its upregulation by K depletion in apical membranes of distal colon, and its physical association with HKc protein provide compelling evidence that HKc is the putative -subunit of colonic H-K-ATPase.

active potassium absorption; rat distal colon; hydrogen-potassium-adenosinetriphosphatase -subunit

This article has been cited by other articles:

				N. B. Pestov, T. V. Korneenko, R. Radkov, H. Zhao, M. I. Shakhparonov, and N. N. Modyanov Identification of the {beta}-subunit for nongastric H-K-ATPase in rat anterior prostate Am J Physiol Cell Physiol, June 1, 2004; 286(6): C1229 - C1237. [Abstract] [Full Text] [PDF]

				W. J. Joiner, S. Basavappa, S. Vidyasagar, K. Nehrke, S. Krishnan, H. J. Binder, E. L. Boulpaep, and V. M. Rajendran Active K+ secretion through multiple KCa-type channels and regulation by IKCa channels in rat proximal colon Am J Physiol Gastrointest Liver Physiol, June 9, 2003; 285(1): G185 - G196. [Abstract] [Full Text] [PDF]

				G. Crambert, J.-D. Horisberger, N. N. Modyanov, and K. Geering Human nongastric H+-K+-ATPase: transport properties of ATP1al1 assembled with different beta -subunits Am J Physiol Cell Physiol, July 1, 2002; 283(1): C305 - C314. [Abstract] [Full Text] [PDF]

				K. Kunzelmann and M. Mall Electrolyte Transport in the Mammalian Colon: Mechanisms and Implications for Disease Physiol Rev, January 1, 2002; 82(1): 245 - 289. [Abstract] [Full Text] [PDF]

				G. Fejes-Toth and A. Naray-Fejes-Toth Immunohistochemical localization of colonic H-K-ATPase to the apical membrane of connecting tubule cells Am J Physiol Renal Physiol, August 1, 2001; 281(2): F318 - F325. [Abstract] [Full Text] [PDF]

				S. Muto Potassium Transport in the Mammalian Collecting Duct Physiol Rev, January 1, 2001; 81(1): 85 - 116. [Abstract] [Full Text] [PDF]

				J. Reinhardt, A. V. Grishin, H. Oberleithner, and M. J. Caplan Differential localization of human nongastric H+-K+-ATPase ATP1AL1 in polarized renal epithelial cells Am J Physiol Renal Physiol, September 1, 2000; 279(3): F417 - F425. [Abstract] [Full Text] [PDF]

				C. T. Okamoto, D. C. Chow, and A. J. G. Forte Interaction of alpha - and beta -subunits in native H-K-ATPase and cultured cells transfected with H-K-ATPase beta -subunit Am J Physiol Cell Physiol, April 1, 2000; 278(4): C727 - C738. [Abstract] [Full Text] [PDF]

				P. Sangan, S. Thevananther, S. Sangan, V. M. Rajendran, and H. J. Binder Colonic H-K-ATPase alpha - and beta -subunits express ouabain-insensitive H-K-ATPase Am J Physiol Cell Physiol, January 1, 2000; 278(1): C182 - C189. [Abstract] [Full Text] [PDF]

				F. Jaisser and A. T. Beggah The nongastric H+-K+-ATPases: molecular and functional properties Am J Physiol Renal Physiol, June 1, 1999; 276(6): F812 - F824. [Abstract] [Full Text] [PDF]