Abstract 061: Interstitial Matrix Flow-Regulation:Myocardial Fibroblasts Respond to Colloidosmotic Pressure

Abstract

Ischemia-reperfusion injury induces large differences in hydration potential between ischemic and nonischemic areas of the myocardium. They influence the rate and volume of fluid transfer in myocardial explants; temperature-dependent hydration-potential differences of approximately 100 mmHg in at-risk areas, as opposed to contiguous areas that are not at risk, suggest prompt interstitial fluid-transfer control mechanisms (Circ. Res . 2012;11:A235) . Aim: We adapted osmotic-stress techniques to determine whether myocardial fibroblasts, which are known to respond to mechanical and flow signals, also respond to hydration-potential changes. Methods: Fibroblasts were isolated from midwall regions of the left ventricles of healthy pigs using standard procedures. They were incorporated into 3-dimensional collagen gels of 500 mm 3 volume at 150 cells/mm 3 and equilibrated overnight in cultures using the nontoxic, inert polymer polyethylene glycol 8000 (molecular radius ~26.5 Å; concentration range 0-10% w/w) to adjust colloidosmotic pressure from approximately 5 to 205 mmHg . After the gels were detached from the dish, fluid flux was derived from any time-dependent changes in their dimensions. Results: The volume of gels without fibroblasts did not change significantly at any coloidosmotic pressure. In those with fibroblasts, the volume decreased, more slowly in those subjected to higher-than-plasma pressure levels. Progression curves conformed well to a two-exponential term model (R 2 >0.9) suggesting that two parallel processes contribute to matrix efflux, one relatively fast, with decay constant 0.274 ± 0.014 (n = 3) , and another ~50-fold slower. Initial rates were calculated from the fitted curves, and linear regression analysis used to examine their dependence on colloidosmotic pressure. Initial efflux rates decreased with pressure, mean slope, - 0.29 ± 0.08 µl/h/mmHg (R 2 = 0.7; P-value = 0.006). Conclusion: In vitro , fibroblasts in collagen matrices regulate fluid efflux in response to colloidosmotic stresses within the range of hydration-potential differences measured in myocardial explants after ischemia-reperfusion injury.