Effect of 17β-estradiol on mRNA expression of large-conductance, voltage-dependent, and calcium-activated potassium channel α and β subunits in guinea pig

Large-conductance, voltage- and calcium-activated potassium (MaxiK) channels play a key role in cell excitability. MaxiK channels are composed of a pore-forming a-subunit and a regulatory P-subunit, of which four (beta1-4) genes have been identified. Previous findings suggested that MaxiK channel activity is regulated by estradiol. However, the underlying mechanisms have remained incompletely documented. Therefore, we used reverse transcriptase polymerase chain reaction to clone four cDNA fragments that were specific to the guinea pig a, beta1, beta2, and beta4 genes. Using a sensitive ribonuclease protection assay, we found that the a and beta4 mRNAs were the most abundant mRNAs in the brain and pituitary, whereas in the aorta, the a-subunit was coexpressed with the beta1-subunit. Moreover, there was a significant upregulation of the alpha- but not the beta1-subunit mRNA and the a-subunit protein in the aorta of the estrogenvs oil-treated ovariectomized animals. In specific brain areas including preoptic area, ventral hypothalamus, hippocampus, and amygdala, and in the pituitary, neither the a- nor beta4-subunit mRNAs were affected by estrogen. These findings suggest that estrogen may not affect the mRNA expression of MaxiK channels in the brain and pituitary. However, estrogen causes increased expression of MaxiK a in the aorta, which may explain some of the cardioprotective effects of estrogen in women.