The regulatory mechanisms in ion channel expression by sexual hormones are urgent issues in the understandings of cardiovascular diseases after menopause, gender difference in occurrence of psychiatric diseases, side effects of hormonal therapy of genital organ cancers. Large conductance Ca2+-activated K+ (BK) channels are activated by changes in membrane potential and/or by increases in concentration of intracellular calcium ion (Ca2+) and substantially contribute to outward K+ currents, modulation of action potential duration and theCa2+-dependent regulation of electrical behaviour in many types of cells including central nervous system and smooth muscles. The activity and/or expression of BK channels can be modulated by steroid hormones as both long-term genomic and acutenon-genomic effects. Female sexual hormones, progesterone and estrogen, regulate BK channel expression andtheir membrane surface clustering in uterine smooth muscles, particularly during pregnancy.We have shown that the expression of BK channels in the amygdala complex is higher in adult (8-10 week old) male rats than in female. Castration at 4-6 weeks old significantly reduces BK channels expression inthe amygdala to a similar level observed in female. Effects of testosterone on the BK channel expression and their functional significance were then investigated in vas deferens smooth muscles (VDSM) of male rats.Western blot analysis showed that castration caused the marked decrease in the expression of BK channel α (BK-α) and β1 (BK-β1) subunits in VDSMC membrane proteins. In contrast, castration did not significantly change expression levels for BK-a and BK-b1 transcripts in VDSMs. We hypothesized that the up-regulation of BK channels expressionin VDSM may be due to the inhibitionof ubiquitin-mediated protein degradation by activation of Androgen Receptors (AR). According to this, we speculated that the down-regulation of BK channel expression, observed in castrated rats, is due the AMPK-activated Ubiquitination of these channels secondary to a decrease of AR activation by testosterone. Therefore we tested the ability of BK channel subunits to bind ubiquitin by co-immunoprecipitation, as well as its ability to bind different Ubiquitin ligase such as Nedd 4, Nedd 4-2 and Cullin 1. Our data suggest that BK-α is indeed able to bind Ubiquitin as well as Nedd 4. In conclusion, AR activation by testosterone critically up-regulates the functional expression of BK channels in VDSMCs, presumably due to inhibition of proteolysis, and thereby substantially modualtes membrane excitability in VDSMs in male rats.