Does actin polymerization contribute to closure of the avian ductus arteriosus ( Gallus gallus )?

• Published in: Physiology (Bethesda, Md.) Md.), 2024-05, Vol.39 (S1)
• Main Authors: Rippamonti, Jessica, Dzialowski, Edward
• Format: Article
• Language: English
• ISSN: 1548-9213; 1548-9221
• DOI: 10.1152/physiol.2024.39.S1.1514

Abstract only The ductus arteriosus (DA) is a cardiovascular embryonic shunt present in all developing land vertebrates. This oxygen-sensitive blood vessel plays the important role of connecting the pulmonary artery to the aorta during development and directs blood flow toward the fetal respiratory organ (placenta in mammals or chorioallantois in birds and reptiles). Permanent vessel closure upon birth or hatch is necessary to establish proper circulation in the neonate. Increased arterial PO 2 at birth or hatch stimulates DA closure via smooth muscle contraction. Smooth muscle contraction, such as in the DA, is governed by myosin light chain kinase (MLCK) stimulating increased cross-bridge cycling, and through increases in actin polymerization. The Ras homologous protein family (Rho) of GTPases are involved in calcium sensitization and contraction of vascular smooth muscle but have mostly been studied for their role in cell migration and signaling. Rho GTPases activate the Rho activated kinase (ROCK) pathway, which works in conjunction with MLCK to generate smooth muscle contraction as well as activating LIM kinase which inhibits the actin depolymerizer cofilin. Rac and Cdc42 GTPase pathways increase contractile strength in smooth muscle cells by activating the nucleator Arp2/3, leading to increased actin polymerization. The role of these GTPase pathways during closure of the DA is unknown. We examined the role of the Rho, Rac, and Cdc42 GTPase pathways leading to actin polymerization for their role in the closure of the avian DA in late-term chicken ( Gallus gallus) embryos. We hypothesized that inhibiting the pathways that lead to actin polymerization will inhibit tension development in the DA. Using a Danish Myo Technology wire myograph, DA physiology was examined when exposed to 25% oxygen followed by activators and inhibitors of the Rho, Rac, and Cdc42 GTPase pathways. Activation of Rho A pathways with CN01 (0.2 units/ml) produced contraction of the DA. Blocking ROCK pathways with Y-27632 (10 mM) removed the O 2 -sensitivity of the vessel, while the vessel was still able to respond to phenylephrine (100 mM). This suggests the Rho pathway is involved in maintaining baseline tension and contractile response to O 2 . Exposure to inhibitors of Rac (10 uM EHT 1864) and Cdc42 (via ML141) GTPases blocked the ability of vessels to contract in response to 25% oxygen, even after 3 hours of constant O 2 . Similarly, inhibition of the Arp2/3 complex (100 uM CK66