Immunocytochemical localization of H(+)-K(+)-ATPase in the rat colon

Purification and characterization of the ouabain-sensitive H+/K+-ATPase from guinea-pig distal colon

Distal colon absorbs K+ through a Na+-independent, ouabain-sensitive H+/K+-exchange, associated to an apical ouabain-sensitive H+/K+-ATPase. Expression of HKalpha2, gene associated with this ATPase, induces K+-transport mechanisms, whose ouabain susceptibility is inconsistent. Both ouabain-sensitive and ouabain-insensitive K+-ATPase activities have been described in colonocytes. However, native H+/K+-ATPases have not been identified as unique biochemical entities. Herein, a procedure to purify ouabain-sensitive H+/K+-ATPase from guinea-pig distal colon is described. H+/K+-ATPase is Mg2+-dependent and activated by K+, Cs+ and NH4+ but not by Na+ or Li+, independently of K+-accompanying anion. H+/K+-ATPase was inhibited by ouabain and vanadate but insensitive to SCH-28080 and bafilomycin-A. Enzyme was phosphorylated from [32P]-gamma-ATP, forming an acyl-phosphate bond, in an Mg2+-dependent, vanadate-sensitive process. K+ inhibited phosphorylation, effect blocked by ouabain. H+/K+-ATPase is an alpha/beta-heterodimer, whose subunits, identified by Tandem-mass spectrometry, seems to correspond to HKalpha2 and Na+/K+-ATPase beta1-subunit, respectively. Thus, colonic ouabain-sensitive H+/K+-ATPase is a distinctive P-type ATPase.

Apical ouabain-sensitive and ouabain-insensitive ATPases in rat colonic epithelium

Active resorption of potassium ions in the colon is mediated by ouabain-sensitive and ouabain-insensitive H,K-ATPases localized in the apical membrane of colonic enterocytes (colonocytes). The present study was performed to investigate distribution patterns of apical ATPases using catalytic histochemistry and immunohistochemistry. Activity of the ATPases was localized both at the apical and basolateral regions of these cells. The basolateral activity was almost completely inhibited by ouabain, but apical ATPase activity was only partially inhibited by ouabain. Ultracytochemically, activity was localized at the cytoplasmic side of the apical and basolateral membrane and thus we assume that the activity represents isoforms of apical H,K-ATPases and basolateral Na,K-ATPase. With the use of a polyclonal antibody raised against H,K-ATPase alpha-subunit, we demonstrated immunostaining only in the apical region of colonic enterocytes whereas positive staining was not observed at the basolateral membrane. On the other hand, when antibodies against alpha1-subunit Na,K-ATPase were applied, immunostaining was localized only in the basolateral membrane domain. Therefore, we conclude that ATPases as demonstrated histochemically in the present study were identified immunohistochemically as colonic alpha-subunit H,K-ATPase (in the apical cell membrane of colonocytes along the entire length of crypts) and as alpha1-subunit Na,K-ATPase (in the basolateral membrane).

Expression and regulation of H+K+ATPase in lysosomes of epithelial cells of the adult rat epididymis

Endocytosis is an important event in the epididymis as it contributes to a luminal environment conducive for sperm maturation. Principal and clear cells contain numerous lysosomes which degrade many substances internalized by endocytosis from the epididymal lumen. The interior of the lysosomes depends on low pH to activate the release of their enzymes and to activate their acid hydrolases. In the present study, H+K+ATPase was localized by light microscopy in the adult rat epididymis of intact and of orchidectomized animals supplemented with testosterone or not. In normal animals, numerous lysosomes of nonciliated cells of the efferent ducts were intensely reactive for anti-H+K+ATPase antibody. In the initial segment, only a few lysosomes of principal cells were reactive. In the intermediate zone of the epididymis, numerous lysosomes of principal cells were intensely reactive, while the number of intensely reactive lysosomes decreased progressively from the proximal caput to the distal caput with none being seen in the proximal corpus region. In the distal corpus and cauda regions, only a few lysosomes of some principal cells were reactive. In contrast, clear cells of all regions showed intense reactivity. Orchidectomy resulted in the abolishion of H+K+ATPase in lysosomes of principal cells of all regions except the initial segment. However, while clear cells of the caput and corpus regions also became unreactive, those of the cauda region remained as reactive as in controls. Orchidectomized animals supplemented with testosterone maintained a staining pattern similar to controls for both cell types. These observations demonstrate the presence in principal and clear cells of H+K+ ATPase which may have an important role in acidifying the interior of their lysosomes. However, there is a region-specific expression of H+K+ATPase in lysosomes of principal cells, unlike that for clear cells. In addition, H+K+ATPase expression in lysosomes of principal cells depends on testosterone in all regions except the initial segment. However, in the case of clear cells, only those of the caput and the corpus regions are dependent on testosterone, while those of the cauda region appear to be regulated by some other factor.

The expression of gastric H+-K+-ATPase mRNA and protein in developing rat fundic gland

The proton pump H+-K+-ATPase is the final common pathway mediating the production and secretion of hydrochloric acid by gastric parietal cells. The present studies were undertaken to examine whether the expression of gastric H+-K+-ATPase mRNA and protein changes are associated with the development of H+-K+-ATPase activity in the rat fundic gland. H+-K+-ATPase activity was examined in rat fundic gland at different stages from gestational day 18.5 to postnatal 8 weeks. The expression of H+-K+-ATPase mRNA was detected by in situ hybridization using a digoxigenin-labelled RNA probe with a tyramide signal amplification system. The expression of H+-K+-ATPase protein was evaluated by immunoblotting and immunohistochemistry using antibodies against H+-K+-ATPase alpha- and beta-subunits. We found that H+-K+-ATPase enzyme activity was detectable from the onset of gland formation (day 19.5 of gestation) and increased with age in the developing rat fundic gland. Expression of mRNA and protein was also discernible at the same time, and a progressive increase in expressions was observed as rats developed. Our results suggested that in developing rat fundic gland, the expression of both mRNA and protein of H+-K+-ATPase increased with age in a manner that parallels the development of H+-K+-ATPase enzyme activity.