Adaptive supersensitivity and the Na+/K+ pump in the guinea pig vas deferens: time course of the decline in the alpha 2 subunit.

Adaptive supersensitivity in the guinea pig vas deferens has been shown previously to be associated with decreases in transmembrane potential, Na+/K+-ATPase activity, [3H]ouabain binding sites, and density of the alpha 2 subunit of the pump. One of several procedures that induce adaptive supersensitivity in the guinea pig vas deferens is neurotransmitter depletion by chronic administration of reserpine. Guinea pigs were treated with reserpine (1.0 mg/kg/day, intraperitoneally) for 2, 5, or 8 days. Tissues were homogenized and the concentration of the alpha 2 subunit was quantified by use of the selective antibody McB2, slot blot analysis, enhanced chemiluminescence, and densitometric analysis. As reported previously, the concentration of the alpha 2 protein was reduced 41% after 5 days of pretreatment. The reduction was maintained at 8 days (37%). However, there was no change from control after 2 days of pretreatment with reserpine. Thus, the time course of the decline in the alpha 2 subunit is similar to that of the appearance of supersensitivity, depolarization, and the declines in Na+/K+-ATPase and [3H]ouabain binding established earlier. Based upon results in the literature for several different tissues and species, membrane depolarization and decreases in Na+/K+ pump sites may represent widely occurring adaptive mechanisms.