Abstract 788: Blockade Of T-type Calcium Channels Attenuates Smooth Muscle Cell Migration, Neointimal Formation, And Oxygen-induced Vascular Contraction In Rat Ductus Arteriosus
Ca2+ influx through voltage-dependent Ca2+ channels regulates vascular remodeling and contraction. However, the role of T-type Ca2+ channels (TCCs) has remained unknown in the ductus arteriosus (DA). Here we hypothesized that Ca2+ influx via TCC contributed to DA closure through promoting neointimal cushion formation and oxygen-induced vascular contraction. Quantitative RT-PCR analysis revealed that α1G, a TCC subtype, was significantly up-regulated in rat neonatal DA tissues at birth and in DA smooth muscle cells (SMCs) that were exposed to oxygen. The expression of α1G mRNA was higher in DA than in the aorta. Immunohistlogical analysis revealed that α1G was localized predominantly to the region of intimal thickening in fetal DA at term and to the central core of neonatal DA at birth. To examine the effects of blockade of TCCs, we used α1G-specific siRNA or R(−)-efonidipine, a highly selective TCC blocker that was recently developed. α1G-specific siRNAs inhibited SMC migration by 55% relative to negative siRNA (n=6, p<0.01). R(−)-efonidipine suppressed SMC migration by 80% relative to control (n=8, p<0.05). Since we have demonstrated that a prostaglandin E receptor EP4 agonist potently promoted physiological intimal thickening (Yokoyama et al. J Clin Invest 2006), we thus examined the effect of R(−)-efonidipine on EP4-mediated intimal cushion formation using DA tissues at preterm in organ culture. Intimal-media ratio of DA stimulated by EP4 was decreased by 60% in the presence of R(−)-efonidipine (n=5, p<0.01), suggesting that Ca2+ influx via TCC contributes to EP4-mediated intimal cushion formation. Finally, we examined the effects of R(−)-efonidipine on oxygen-induced vascular contraction using a vascular ring of fetal DA at term. R(−)-efonidipine attenuated oxygen-induced vascular contraction in a dose-dependent manner. Isometric tension induced by oxygen was decreased by 60% in the presence of 10−5M of R(−)-efonidipine. In conclusion, TCC, especially α1G, blockade attenuated SMC migration, neointimal formation, and oxygen-induced vascular contraction in rat DA. The present study implies that TCC blockade is an alternative therapeutic strategy to keep DA open for patients with DA-dependent congenital heart defects.