T-type Ca2+ Channels Promote Oxygenation-induced Closure of the Rat Ductus Arteriosus Not Only by Vasoconstriction but Also by Neointima Formation (original) (raw)

2009, Journal of Biological Chemistry

The ductus arteriosus (DA), an essential vascular shunt for fetal circulation, begins to close immediately after birth. Although Ca 2؉ influx through several membrane Ca 2؉ channels is known to regulate vasoconstriction of the DA, the role of the T-type voltage-dependent Ca 2؉ channel (VDCC) in DA closure remains unclear. Here we found that the expression of ␣1G, a T-type isoform that is known to exhibit a tissue-restricted expression pattern in the rat neonatal DA, was significantly upregulated in oxygenated rat DA tissues and smooth muscle cells (SMCs). Immunohistological analysis revealed that ␣1G was localized predominantly in the central core of neonatal DA at birth. DA SMC migration was significantly increased by ␣1G overexpression. Moreover, it was decreased by adding ␣1G-specific small interfering RNAs or using R(؊)-efonidipine, a highly selective T-type VDCC blocker. Furthermore, an oxygenationmediated increase in an intracellular Ca 2؉ concentration of DA SMCs was significantly decreased by adding ␣1G-specific siRNAs or using R(؊)-efonidipine. Although a prostaglandin E receptor EP4 agonist potently promoted intimal thickening of the DA explants, R(؊)-efonidipine (10 ؊6 M) significantly inhibited EP4-promoted intimal thickening by 40% using DA tissues at preterm in organ culture. Moreover, R(؊)-efonidipine (10 ؊6 M) significantly attenuated oxygenation-induced vasoconstriction by ϳ27% using a vascular ring of fetal DA at term. Finally, R(؊)-efonidipine significantly delayed the closure of in vivo DA in neonatal rats. These results indicate that T-type VDCC, especially ␣1G, which is predominantly expressed in neonatal DA, plays a unique role in DA closure, implying that T-type VDCC is an alternative therapeutic target to regulate the patency of DA. The ductus arteriosus (DA) 2 is an essential vascular shunt between the aortic arch and the pulmonary trunk during a fetal period (1). After birth, the DA closes immediately in accordance with its smooth muscle contraction and vascular remodeling, whereas the connecting vessels such as the aorta and pulmonary arteries remain open. When the DA fails to close after birth, the condition is known as patent DA, which is a common form of congenital heart defect. Patent DA is also a frequent problem with significant morbidity and mortality in premature infants. Investigating the molecular mechanism of DA closure is important not only for vascular biology but also for clinical problems in pediatrics. Voltage-dependent Ca 2ϩ channels (VDCCs) consist of multiple subtypes, named L-, N-, P/Q-, R-, and T-type. L-type VDCCs are known to play a primary role in regulating Ca 2ϩ influx and thus vascular tone in the development of arterial smooth muscle including the DA (2-4). Our previous study demonstrated that all T-type VDCCs were expressed in the rat DA (5). ␣1G subunit, especially, was the most dominant isoform among T-type VDCCs. The abundant expression of ␣1G subunit suggests that it plays a role in the vasoconstriction and vascular remodeling of the DA. In this regard, Nakanishi