Mechanisms of urinary K+ and H+ excretion: primary structure and functional expression of a novel H,K-ATPase

Ouabain resistance of the epithelial cell line (Ma104) is not due to lack of affinity of its pumps for the drug

Na+, K(+)-pumps of most eukaryotic animal cells bind ouabain with high affinity, stop pumping, and consequently loose K+, detach from each other and from the substrate, and die. Lack of affinity for the drug results in ouabain resistance. In this work, we report that Ma104 cells (epithelial from Rhesus monkey kidney) have a novel form of ouabain-resistance: they bind the drug with high affinity (Km about 4 x 10(-8) M), they loose their K+ and stop proliferating but, in spite of these, up to 100% of the cells remain attached in 1.0 microM ouabain, and 53% in 1.0 mM. When 4 days later ouabain is removed from the culture medium, cells regain K+ and resume proliferation. Strophanthidin, a drug that attaches less firmly than ouabain, produces a similar phenomenon, but allows a considerably faster recovery. This reversal may be associated to the fact that, while in ouabain-sensitive MDCK cells Na+, K(+)-ATPases blocked by the drug are retrieved from the plasma membrane, those in Ma104 cells remain at the cell-cell border, as if they were cell-cell attaching molecules. Cycloheximide (10 micrograms/ml) and chloroquine (10 microM) impair this recovery, suggesting that it also depends on the synthesis and insertion of a crucial protein component, that may be different from the pump itself. Therefore ouabain resistance of Ma104 cells is not due to a lack of affinity for the drug, but to a failure of its Na+, K(+)-ATPases to detach from the plasma membrane in spite of being blocked by ouabain.

Cloning and characterization of the entire cDNA encoded by ATP1AL1--a member of the human Na,K/H,K-ATPase gene family

The cDNA for ATP1AL1--the fifth member of the human Na,K-/H,K-ATPase gene family--was cloned and sequenced. The deduced primary ATP1AL1 translation product is 1,039 amino acids in length and has Mr of 114,543. The encoded protein has all of the structural features common to known catalytic subunits of P-type membrane ion-transporting ATPases and is equally distant (63-64% of identity) from the Na,K-ATPase isoforms and the gastric H,K-ATPase. The ATP1AL1 encoded protein was proposed to represent a new separate group within the family of human potassium-dependent ion pumps.

Primary sequence and functional expression of a novel beta subunit of the P-ATPase gene family

The cortical collecting tubule (CCT) of the mammalian kidney reabsorbs sodium and potassium, processes that are mediated by Na/K-ATPase and H/K-ATPase. CCT is also an important site for proton secretion, which is driven, in part, by H/K-ATPase. Na/K-ATPase and H/K-ATPase are members of the ion-motive P-ATPase gene family. They are closely related plasma membrane proteins which consist of alpha beta heterodimers. The urinary bladder of the toad Bufo marinus is the amphibian counterpart of mammalian CCT. We have previously characterized a ouabain-resistant Na/K-ATPase [see ref. 17], from TBM cells, a clonal cell line derived from the toad bladder, which expresses transepithelial sodium transport. In the present study, we report the primary sequence and functional expression of a novel beta subunit (beta bladder = beta b1) isolated from a toad bladder epithelial cell cDNA library. The deduced polypeptide is 299 amino acids in length and has a predicted molecular mass of 33 kDa. The beta b1 protein exhibits 35% amino acid identity to the previously characterized beta 1 of B. marinus Na/K-ATPase and 39% identity with beta 3 of B. marinus Na/K-ATPase. It shares 38% identity with the mammalian beta gastric H/K-ATPase and 52% with the mammalian beta 2 Na/K-ATPase. Northern blot analysis shows that a 1.4 x 10(3)-base mRNA is expressed at a high level in bladder epithelial cells and eye and at a trace level in kidney; it is not detectable in significant amounts in the stomach, colon and small intestine.(ABSTRACT TRUNCATED AT 250 WORDS)