Cytoskeletal features in longitudinal and circular smooth muscles during development of the rat portal vein

Abstract

Immunohistochemistry of alpha-smooth muscle actin and desmin, two markers of smooth muscle cell differentiation, and electron-microscopic observation of thick filaments of myosin were performed on the media of the developing rat hepatic portal vein to gain insights into the chronology of differentiation of its longitudinal and circular smooth muscles. In accordance with the ultrastructural distribution of thin filaments, staining of alpha-smooth muscle actin is lightly positive in the myoblasts at postnatal day 1 and then extends in probably all muscle cells of the developing vessel. Desmin, which appears later than alpha-smooth muscle actin in the two muscles, is distributed throughout the longitudinal layer at day 8, whereas the first arrangements of thick filaments are detectable in most longitudinal muscle cells; at this stage, desmin and thick filaments are absent from the poorly differentiated circular muscle cells. The longitudinal muscle cells differentiate in a strikingly synchronized way from day 8 onwards, conferring a homogeneous structure to the developing and mature longitudinal layer. Several desmin-positive cells and a heterogeneous distribution of thick filaments occur in the circular muscle at day 14; the subsequent extension of these filaments in this layer results in a persisting heterogeneous distribution in the young 7-week-old adult. Many features of the mature smooth muscle cells are established within the third week in the longitudinal muscle, approximately one week before those of the circular layer. These results are consistent with the function of the longitudinal muscle as a spontaneously contractile smooth muscle unit, and emphasize the need for its fast maturation to fulfil its major role in the control of portal blood flow.

Molecular Mechanisms of Adiponectin-Induced Attenuation of Mechanical Stretch-Mediated Vascular Remodeling

“…In order to achieve these aims, the rat portal vein (RPV) was mechanically stretched in a wellcharacterized organ culture model to mimic hypertension [23,25,[55][56][57]. The RPV has distinct musculature; its tunica media is composed of an outer, thick layer of longitudinally oriented VSMCs, whereas its inner, thin layer has circularly oriented VSMCs [58,59]. In order to mimic hypertension, the RPV was stretched with weights that lead to 10-15% stretch, which has been calculated using the force-length relationship [57,58,60].…”

Stretch‐Dependent Smooth Muscle Differentiation in the Portal Vein—Role of Actin Polymerization, Calcium Signaling, and microRNAs

“…The wall of the portal vein comprises a thin inner circular muscle layer and a thicker outer longitudinal layer. In the rat, these muscle layers are weakly developed at birth but the longitudinal muscle layer develops well organized contractile and cytoskeletal filaments as well as spontaneous activity in the first three postnatal weeks, whereas the circular layer is less filamentous, lacks spontaneous activity, and is fully developed approximately one week later . These differences may reflect stretch‐regulated development primarily of the longitudinal muscle layer for propelling blood and maintaining the integrity of the vessel in the anatomical absence of major longitudinal supporting structures.…”

Independent endothelial functions of PIEZO1 and TRPV4 in hepatic portal vein and predominance of PIEZO1 in mechanical and osmotic stress

“…It is an active vessel, helping to propel or restrict blood flow to the liver and modulating changes in the liver, such as its regeneration, by altering shear stress and stimulating angiogenesis 3 . The vein is lined by endothelium, has a medial layer containing smooth muscle cells arranged circularly and longitudinally, and is innervated 4–6 . Its contractile properties are influenced by chemical factors including noradrenaline, acetylcholine and angiotensin II 6 and mechanical and osmotic factors arising from changes in vessel length, wall tension, blood flow and blood water content 7–10 .…”

“… 3 The vein is lined by endothelium, has a medial layer containing smooth muscle cells arranged circularly and longitudinally, and is innervated. 4 , 5 , 6 Its contractile properties are influenced by chemical factors including noradrenaline, acetylcholine and angiotensin II 6 and mechanical and osmotic factors arising from changes in vessel length, wall tension, blood flow and blood water content. 7 , 8 , 9 , 10 Flow through the portal vein increases or decreases physiologically, for example, after a meal or during physical exercise.…”