The catalytic alpha- and smaller glycosylated beta-subunits of the membrane transport enzyme Na(+)-K(+)-adenosinetriphosphatase (ATPase) occur in different molecular forms, alpha 1, alpha 2, alpha 3, beta 1, and beta 2. The catalytic alpha 1-, alpha 2-, and alpha 3-subunits of the enzyme have varying affinities for digitalis and exist in different tissues with unique distribution patterns. In this report we document for the first time the existence of alpha 1-, alpha 2-, alpha 3-subunit proteins (all approximately 97.5 kDa) in cultured rat aortic smooth muscle cells and rat tail arteries. In addition to the three molecular forms of the alpha-protein we detected a minor band at approximately 68-kDa position in aortic smooth muscle cells, which may correspond to the truncated alpha 1-protein reported earlier.