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

AbstractWe have assessed the Na pump α-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 α1 subunit (~100 kDa) as well as a truncated subunit, α1T (~66 kDa). SDS treatment of VSM microsomes effected an increase in Na+,K+-ATPase and a retention of α1T. SDS treated kidney microsomes retained the α1 isoform and Na+,K+-ATPase. Confluent VSM cells showed no detectable α1T, only α1T. In the absence of detectable full length α1, the α1T protein may represent a functional Na pump component in canine VSM