Down-regulation of Na+/K+-ATPase α2 isoform in denervated rat vas deferens

In the rat vas deferens, an organ richly innervated by peripheral sympathetic neurons, we have demonstrated recently the expression of alpha(1) and alpha(2), but not alpha(3) isoforms of the a subunit of Na+/K+-ATPase (EC 3.6.1.37), a membrane-bound enzyme of vital function for living cells (Noel et al., Biochem Pharmacol 55: 1531-1535, 1998). In the present work, we characterized, qualitatively and quantitatively, Na+/K+-ATPase a isoforms in denervated rat vasa deferentia. [H-3]Ouabain binding at concentrations defined for high-affinity isoforms (alpha(2) and/or alpha(3)) detected only one class of specific binding sites in control (C) and denervated (D) vas deferens. Although the dissociation constant was similar for both groups [K-d = 138 +/- 14 nM (C) and 125 +/- 8 nM (D)], a marked decrease in density was observed after denervation [716 +/- 81 fmol(.)mg protein(-1) (C) and 445 +/- 34 fmol(.)mg protein(-1) (D), P < 0.05]. In addition, western blotting revealed that denervated vasa deferentia produce the alpha(1) and alpha(2) isoforms but not alpha(3), just as we reported for the controls previously (Noel et al., Biochem Pharmacol 55: 1531-1535, 1998). Densitometric analysis showed a decrease of the alpha(2) isoform by about 4094 in denervated organs, in very good agreement with what was shown with the [H-3]ouabain binding technique, but no significant change in oil isoform density. Truncated alpha(1) (alpha(1)T), an isoform suggested to exist in the guinea pig vas deferens, was not detected. Altogether, our results demonstrated that Na+/K+-ATPase alpha(2) is down-regulated after sympathetic denervation of the rat vas deferens. (C) 2000 Elsevier Science Inc.