Multiple transcripts of Ca 2ϩ channel ␣ 1 -subunits and a novel spliced variant of the ␣ 1C -subunit in rat ductus arteriosus

3 H]thymidine incorporation, suggesting that L-and T-type Ca 2ϩ channels are involved in smooth muscle cell proliferation in the DA. Third, we found that a novel alternatively spliced variant of the ␣ 1C-isoform was highly expressed in the neointimal cushion of the DA, where proliferating and migrating smooth muscle cells are abundant. The basic channel properties of the spliced variant did not differ from those of the conventional ␣1C-subunit. We conclude that multiple VDCC subunits were identified in the DA, and, in particular, ␣ 1C-and ␣1G-subunits were predominant in the DA. A novel spliced variant of the ␣1C-subunit gene may play a distinct role in neointimal cushion formation in the DA. alternative spliced; development; gene expression; fetal circulation THE DUCTUS ARTERIOSUS (DA) is a fetal arterial connection between the pulmonary artery and the descending aorta. After birth, the DA closes immediately, in accordance with its smooth muscle contraction. An increase in oxygen tension and a dramatic decline in circulating prostaglandins are the most important triggers of DA contraction (5). Generally, vascular smooth muscle contraction is induced by Ca 2ϩ / calmodulin-dependent phosphorylation of the regulatory myosin light chain, which is mediated by an increase in intracellular Ca 2ϩ . Ca 2ϩ influx through voltage-dependent Ca 2ϩ channels (VDCCs) and Ca 2ϩ release from intracellular stores are major sources of this increase (8, 26). Thus VDCCs must play an important role in vascular myogenic reactivity and tone of the DA. VDCCs are classified, according to their distinct electrophysiological and pharmacological properties, into low (Ttype) and high (L-, N-, P-, Q-, and R-type) VDCCs (20, In addition to their role in determining contractile state, a growing body of evidence has demonstrated that VDCCs play an important role in regulating differentiation and remodeling of vascular smooth muscle cells (SMCs) (14, In the present study, we identified multiple VDCC subunits in the DA by semiquantitative and quantitative RT-PCR and immunodetection. In particular, ␣ 1C -and ␣ 1G -subunits were predominant in the DA. Furthermore, we will demonstrate the identification of a novel spliced variant of the ␣ 1C -subunit gene that may play a role in neointimal cushion formation of the DA

Post-transcriptional downregulation of sarcolipin mRNA by triiodothyronine in the atrial myocardium

AbstractThyroid hormone-mediated positive cardiotropic effects are differently regulated between the atria and ventricles. This regulation is, at least in part, dependent on sarcoplasmic reticulum (SR) proteins. Sarcolipin, a homologue of phospholamban, has been recently identified as an atrium-specific SR protein. The expression of sarcolipin mRNA was significantly decreased in the atria of mice with hyperthyroidism and in 3,5,3′-triiodo-l-thyronine-treated neonatal rat atrial myocytes. Promoter activity and mRNA stability analyses revealed that thyroid hormone post-transcriptionally downregulated the expression of sarcolipin mRNA. The atrium-specific effect of thyroid hormone may occur in part through the regulation of atrial sarcolipin gene expression