Macromolecular permeability of endothelial cells subjected to biochemical and mechanical stimuli
Wagner, John E.
McIntire, Larry V.
Doctor of Philosophy thesis
Endothelial cells line all of the vessels of the circulatory system, providing a non-thrombogenic conduit and form the principal barrier to the transport of substances between the blood and the surrounding tissue. The endothelial barrier is particularly important in the brain since neural function depends on the maintenance of a constant cererbro-spinal fluid composition. The changes in macromolecular permeability of brain microvessel (BMECs) and pulmonary artery (CPA-47s) endothelial cells subjected to fluid shear stress and the physiological mediators atrial natriuretic peptide (ANP) and thrombin were studied. Endothelial cells were grown on a permeable polycarbonate membrane and subjected to different biochemicals or shear stress. The permeability properties of the cells were quantitated by measuring the flux of labeled albumin or dextran that passed through the cell monolayer and the permeability coefficient (P) was calculated. The permeability coefficient of albumin for the BMECs (3.3 $\pm$ 0.2) nm/s was over an order of magnitude less than that of the CPA-47s (58 $\pm$ 4) nm/s. Addition of thrombin dramatically increased the permeability of both the cell types in a dose dependent manner and this effect was modulated by cyclic AMP in CPA-47s but not in BMECs. Neither ANP or cyclic GMP significantly altered thrombin's effect in either cell type. Ionophore A23187, or protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate (PMA), both dramatically increased albumin permeability in both cell types in a dose dependent manner. PMA's effect was reversible over time and was inhibited by the PKC inhibitor H7 but not HA-1004. Shear stress of 1 dyne/cm$\sp2$ did not produce any large scale morphological changes in BMECs but did cause an increase in macromolecular permeability. Shear stress of 10 dynes/cm$\sp2$ induced the brain cells to take on a cobblestone morphology before elongating in the direction of flow. This higher shear stress level also induced an increase in macromolecular permeability that was maximal between 10 and 20 hours and returned to near baseline values after 60 hours in the shear field.
Biomedical engineering; Chemical engineering; Physiology; Biology; Engineering