Porcine aortic valve interstitial cells exhibit dual structural and functional characteristics of myofibroblasts, including matrix secretion and contractile responses to vasoactive stimuli.
Porcine aortic valve interstitial cells function as myofibroblasts, possessing both contractile and matrix-secreting properties that may contribute to valve durability.
The cellular properties of semilunar cardiac valve leaflets may be more complex than previously assumed. In particular, the cells of the leaflet matrix which are likely critical to proper cusp function are a poorly described population to date. We hypothesized that, similar to the matrix cells of atrioventricular valves, aortic valve leaflet interstitial cells (AoLIC's) possess characteristics of both fibroblasts (matrix secretion) and smooth muscle cells (contraction). Porcine AoLIC's were structurally examined for contractile and stress fiber protein assemblies using transmission electron microscopy and immunocytochemistry. Contractile function in response to vasoactive stimuli was directly assessed using AoLIC's cultured on flame-polymerized silicone, with cell contraction identified by the appearance of wrinkles in the substratum after challenge with each agent. The structural analyses showed cellular microfilaments were often organized into various contractile arrangements including polygonal networks, and that AoLIC's are rich in smooth muscle-specific alpha-actin. Incomplete basal laminae often associated with myofibroblasts were observed. Contraction experiments indicated a responsivity of similar latency, but variable peak and duration to 10(-7) M L-epinephrine, 3.2 x 10(-7) M angiotensin II, 110 microM carbachol, 50 mM KCl, 3.2 x 10(-7) M bradykinin, 110 microM isoproterenol, and 5 x 10(-7) M endothelin I. Soluble and insoluble matrix secretion was confirmed with FITC-conjugated monoclonal antibodies to chondroitin sulfate, fibronectin, and prolyl-4-hydroxylase. These data show that the AoLIC's are best designated as myofibroblasts. The unusual features of the myofibroblast may be central to lifelong aortic leaflet durability.
Messier et al. (Fri,) conducted a other in Aortic valve interstitial cell characteristics. Vasoactive stimuli was evaluated on Structural characteristics and contractile function. Porcine aortic valve interstitial cells exhibit dual structural and functional characteristics of myofibroblasts, including matrix secretion and contractile responses to vasoactive stimuli.