Sodium pump isozymes are differentially expressed in electrically dissimilar regions of colonic circular smooth muscle.

Molecular analyses of Na,K-ATPase abundance and alpha-subunit isoform distribution were performed to determine whether pump expression varies at different points through the thickness of the circular layer of colonic smooth muscle. The mRNA and polypeptides of Na,K-ATPase alpha 1 and beta subunits were twice as abundant in the submucosal region of the circular layer, which has previously been shown to generate large pump potentials. Sodium pump activity directly correlated with the relative abundance of the alpha 1 polypeptide. These data show that sodium pump expression varies in electrically dissimilar regions of the circular layer.