BLOOD-FLOW SENSING BY ANIONIC BIOPOLYMERS

Using Na-23-NMR techniques we could show that the polyanion proteohepa ran sulfate integrated into the membrane of endothelial cells may serv e as 'flow sensor', Based on its viscoelastic properties, heparan sulf ate proteoglycan is present as a random coil under 'no flow' condition s, whereby most of its polyanionic sites undergo intramolecular hydrog en bonding. With increasing flow the macromolecule becomes unfolded in to a filamentous structure. Additional anionic binding sites to which Na+ ions from the blood bind are released by this shear stress-depende nt conformational change, The Na+ binding triggers the signal transduc tion chain for a vasodilatory vessel reaction, Decrease in flow effect s, for reasons of the intramolecular elastic recoil forces of the macr omolecules, an entropic coiling, the release of Na+ ions and thus an i nterruption of the signal chain. Proteoheparan sulfate adsorbed onto a hydrophobic surface in physiological Krebs solution at pH 7.3 demonst rated clearly its characteristic as a Na+ sensor, While Ca2+ ions modu lated the adsorption (promotion with increasing Ca2+ concentrations) b y changing the conformation of the sensor molecule, the adsorbed amoun t was determined preferably by the Na+ concentration. K+ and Mg2+ ions showed slightly desorbing properties with increasing concentrations, Thus, it may be concluded that Na+ ions play the role as 'first messen ger' in flow-dependent vasodilatation.