17Beta-Estradiol Inhibits Calcium-Activated Potassium Channel Expressions in Rat Whole Bladder

PURPOSE To investigate the effect of estrogen on the expression of calcium-activated potassium (KCa) channels in an overactive bladder rat model. To this end, mRNA and protein levels of KCa channel subtypes in the bladder of ovariectomized rats were measured by reverse transcription polymerase chain reaction and western blotting, respectively. METHODS Ten-week-old female Sprague-Dawley rats were divided randomly into 3 groups: sham-operated control group (n=11), ovariectomy group (n=11), and the group treated with estrogen after ovariectomy (n=12). Rats in the last group were subcutaneously injected with 17β-estradiol (50 μg/kg) every other day for 2 weeks, whereas rats in the other 2 groups received vehicle (soybean oil) alone. Two weeks after treatment, the whole bladder was excised for mRNA and protein measurements. RESULTS Protein levels of the large-conductance KCa (BK) channels in the ovariectomy group were 1.5 folds higher than those in the sham-operated control group. However, the protein levels of the other KCa channel subtypes did not change significantly upon bilateral ovariectomy. Treatment with 17β-estradiol after ovariectomy restored BK channel protein levels to the control value. In contrast, BK channel mRNA levels were not significantly affected by either ovariectomy alone or 17β-estradiol treatment. The small-conductance KCa type 3 channel (SK3) mRNA and protein levels decreased to 75% of control levels upon 17β-estradiol treatment. CONCLUSIONS These results suggest that 17β-estradiol may influence urinary bladder function by modulating BK and SK3 channel expression.