Tissue specific membrane association of α1T, a truncated form of the α1 subunit of the Na pump

We have assessed the Na pump alpha-subunit isoform content utilizing site directed antibodies in two vascular smooth muscle (VSM) preparations known to contain functional Na pump sites, VSM microsomal fractions (Na+, K(+)-ATPase) and intact primary confluent cells (ouabain inhibited 86Rb uptake). A comparison of isoform content was made with kidney microsomes. Both VSM and kidney microsomes contained a full length alpha 1 subunit (approximately 100 kDa) as well as a truncated subunit, alpha 1T (approximately 66 kDa). SDS treatment of VSM microsomes effected an increase in Na+, K(+)-ATPase and a retention of alpha 1T. SDS treated kidney microsomes retained the alpha 1 isoform and Na+, K(+)-ATPase. Confluent VSM cells showed no detectable alpha 1, only alpha 1T. In the absence of detectable full length alpha 1, the alpha 1T protein may represent a functional Na pump component in canine VSM.