17β-estradiol regulation of the mRNA expression of T-type calcium channel subunits: Role of estrogen receptor α and estrogen receptor β

Low-voltage-activated (T-type) calcium channels are responsible for burst firing and transmitter release in neurons and are important for exocytosis and hormone secretion in pituatary cells. T-type channels contain an α1 subunit, of which there are three subtypes, Cav3.1, -3.2, and -3.3, and each subtype has distinct kinetic characteristics. Although 17β-estradiol (E2) modulate T-type calcium channel expression and function, little is known about the molecular mechanisms involved. We used real-time PCR quantification of RNA extracted from hypothalamic nuclei and pituitary in vehicle and E2-treated C57BL/6 mice to elucidate E2-mediated, regulation of Cav3.1, -3.2, and -3.3 subunits. The three subunitis expressed in both the hypothalamus and the pituitary. E2 treatment increased the mRNA expression of Cav3.1 and -3.2, but not Cav3.3, in the medial preotic are and the arcuate nucleus. In the pituitary, Cav3.1 was increased with E2 treatment, and Cav3.2 and -3.3 were decreased. To examine whether the classical estrogen receptors (ERs) were involved in the regulation, we used ERα- and ERβ-deficient C57BL/6 mice and explored the effects of E2 on T-type channel subtypes. Indeed, we found that the E2-induced increase in Cav3.1 in the hypothalamus was dependent on ERα whereas the E2 effect on Cav3.2 was dependent on both ERα and ERβ. However, the E2-induced effects in the pituitary were dependent on only the expression of ERα. The robust E2 regulation of T-type calcium channels could be an important mechanism by which E2 increases the excitability of hypothalamic neurons and modulates pituitary secretion.