ADAPTIVE SUPERSENSITIVITY IN THE GUINEA-PIG VAS-DEFERENS IS ASSOCIATED WITH A REDUCTION IN THE ABUNDANCE OF THE ALPHA-2 SUBUNIT ISOFORM OF NA+ K+-ATPASE/

Adaptive supersensitivity has been demonstrated previously in the guin ea pig vas deferens after chronic treatment with reserpine, postgangli onic denervation, or preganglionic denervation. The magnitude of the c hange in sensitivity was similar regardless of the method of induction ; the underlying mechanism was identified as a partial depolarization secondary to reduced activity of the Na+/K+ pump. Experiments were con ducted to quantitatively determine whether the identified losses in Na +/K+-ATPase activity and [H-3]ouabain binding were due to reductions i n the levels of specific protein subunits of the sodium pump. Electrop horetic separation and quantification of the abundance of alpha subuni t isoforms were accomplished using sodium dodecyl sulfate-polyacrylami de gel electrophoresis and slot blot analysis. Supersensitivity was in duced in the guinea pig vas deferens through pretreatment with reserpi ne (1.0 mg/kg/day x 5 days). The abundance of the alpha2 subunit isofo rm was reduced by 41% in tissue homogenates obtained from animals trea ted with reserpine, compared with untreated controls. In contrast, the re was no significant alteration in the alpha1 subunit isoform (a prot ein similar in size to that previously identified in vascular smooth m uscle as a ''truncated'' form of the protein). These data suggest that the adaptation of the guinea pig vas deferens after a chronic reducti on in net stimulus is mediated through a change in a specific cellular protein. This evidence supports the assignment of the alpha2 subunit isoform as the specific protein responsible for the development of non specific adaptive supersensitivity in the guinea pig vas deferens.