(Na+ + K+)-ATPase and plasma membrane polarity of intestinal epithelial cells: presence of a brush border antigen in the distal large intestine that is immunologically related to beta subunit.

Abstract

Abstract. The previously produced monoclonal antibody IEC 1/48 against cultured rat intestinal crypt cells (Quaroni, A., and K. J. Isselbacher. 1981. J. Natl. Cancer Inst. 67:1353-1362 was extensively characterized and found to be directed against the/3 subunit of (Na + + K÷)-ATPase as assessed by immunological and enzymatic criteria. Under nondenaturing conditions the antibody precipitated the ct-/~ enzyme complex (98,000 and 48,000 Mr). This probe, together with the monoclonal antibody C 62.4 against the c~ subunit (Kashgarian, M., D. Biemesderfer, M. Caplan, and B. Forbush. 1985. Kidney Int. 28:899-913), was used to localize (Na + + K÷)-ATPase in epithelial cells along the rat intestinal tract by immunofluorescence and immunoelectron microscopy. Both antibodies exclusively labeled the basolateral membrane of small intestine and proximal colon epithelial cells. However, in the distal colon, IEC 1/48, but not C 62.4, also labeled the brush border membrane. The cross-reacting/~-subunit-like antigen on the apical cell pole was tightly associated with isolated brush borders but was apparently devoid of (Na + + K÷)-ATPase activity. Subcellular fractionation of colonocytes in conjunction with limited proteolysis and surface radioiodination of intestinal segments suggested that the cross-reacting antigen in the brush border may be very similar to the fl subunit. The results support the notion that in the small intestine and proximal colon the enzyme subunits are exclusively targeted to the basolateral membrane while in the distal colon nonassembled/3 subunit or a ~-subunit-like protein is also transported to the apical cell pole.

Functional expression and segmental localization of rat colonic K-adenosine triphosphatase.

“…This latter possibility is suggested by the demonstration that the P subunits of Na,K-ATPase and H,K-ATPase can serve as partial surrogates in the activation of both H,K-ATPase and Na,K-ATPase activities, respectively (21). This suggestion is further supported by the previous observation that an antibody to the P subunit of Na,K-ATPase identified a protein in the apical membrane of rat distal colon (22). Further studies of the role of a putative colonic K-ATPase /3 subunit are required.…”

A nervous system-specific isotype of the beta subunit of Na+,K(+)-ATPase expressed during early development of Xenopus laevis.

“…As discussed above, the Xenopus (33 subunit is more closely related to the mammalian ,(2 than the ,(1 sequence and might, therefore, function in neuronal and glial cell interactions. In a different system, the ( subunit of Na+,K+-ATPase has been found in parts of the cell where no Na',K+-ATPase activity or a subunit protein was detected (47). Thus, (3 subunits may have dual functions in general, or certain (3subunits may not be part of the Na+,K+-ATPase at all but have an entirely separate role.…”

The β‐subunit of the gastric H+/K+‐ATPase can occur without the α‐subunit

“…Previous immunohistochemical studies suggest that the ~-subu~t of the NaC /K+ -ATPase also exists in two populations [20]. In the basolateral membranes of epithelial cells from rat distal colon P-subunit is detected together with a-subunit.…”