Properties of a novel splicing variant of ATP1AL1, a human non-gastric proton pump

Abstract

Rat non-gastric H⁺,K⁺-ATPase is highly expressed in the distal colon and may be associated with K⁺ conservation in the colon. But physiological function of human non-gastric H⁺,K⁺-ATPase (ATP1AL1) has not been clarified yet. Here, we have cloned a normal type (NT) and a novel splicing valiant deleting exon4 (Δexon4) of ATP1AL1. Then, the stable cell lines expressing gastric H⁺,K⁺-ATPase β-subunit (gHKβ) were transfected with the pcDNA4/His-ATP1AL1 cDNA (NT or Δexon4) construct. The activities of the K⁺-dependent ATPase and the ⁸⁶Rb⁺ uptake of ATP1AL1 were estimated by subtracting 1 mM ouabain-sensitive activity from 5 μM ouabain-sensitive activity. These activities of ATP1AL1 were also measured by using 100 μM SCH 28080, an inhibitor of gastric H⁺,K⁺-ATPase. We found that Δexon4 is expressed in the plasma membrane of the cells. Similar to the case for NT, the gHKβ was required for expression of Δexon4. We found that Δexon4 has no activities of the K⁺-dependent ATPase and the ⁸⁶Rb⁺ uptake. When NT and Δexon4 were co-transfected into the stable cell lines expressing gHKβ, the ⁸⁶Rb⁺ uptake activity was significantly lower than that in the cells transfected with NT alone. Apparently, Δexon4 had no effect on the level of expression of NT in the cells. These results suggest that Δexon4 exerts a dominant negative effect on NT. [J Physiol Sci. 2006;56 Suppl:S71]