Fluid Transport in the Extracellular Matrix:Kinetic Changes Induced by Metabolic Inhibitors

Abstract

Water and solutes are transported to and from cells across the extracellular matrix by osmo-mechanical forces, the fiber-mesh, glycosaminoglycans, and myofibroblasts in as yet unclear ways. Here, we analyze fluid transfer in/out of the dermal matrix as a function of pressure and time and explore the effects of glucose-metabolism inhibitors. Osmotic-stress techniques were adapted to measure transfer-kinetics in full-thickness dermal cultures at six different polyethylene glycol concentrations adjusted by membrane osmometry (range =3-211 mmHg). Influx/outflux at each pressure was followed over time by precision weighing. Progression curves were modeled using: Volume Transfer = Vmax/[1+(time/T1/2)d] , where Vmax is total volume transferred; T1/2 is the time at which volume is half-maximal; and d is proportional to the rate at T1/2. Rates and Vmax were found to be proportional to pressures and varied with temperature, as did the pH of cultures, suggesting that flow regulation is energy-dependent. Na Azyde (0.4mg-2.5 mg/ml) increased outflow, while Iodoacetamide (1.8-4.5 mg/ml) decreased it relative to that in explants without inhibitors; at 208 mmHg, Vmax values were 0.438 ± 0.0058 (Na Azyde); 0.284 ± 0.036 (Iodoacetamide); 0.359 ± 0.029 (control) below the initial value. Inflow increased with inhibitors; at 3 mm Hg, Vmax values were 0.392 ± 0.032, 0.463 ± 0.093, and 0.265± 0.012 above the initial volume, respectively. With the caveat that the inhibitors' effects on transfer could be unrelated to changes in the myofibroblasts' glucose metabolism, these differences suggest that energy for flow regulation is derived primarily from anaerobic metabolism during outflow but from aerobic and anaerobic metabolism during inflow. Globally, these observations are consistent with a model where myofibroblasts respond to pressure and oxygenation changes by adjusting fiber tension to control glycosaminoglycans hydration.