J. Phys. Colloques
Volume 45, Numéro C2, Février 1984
10ème Congrès International d'Optique des Rayons X et de Microanalyse
10th International Congress on X-Ray Optics and Microanalysis
Page(s) C2-595 - C2-598
10ème Congrès International d'Optique des Rayons X et de Microanalyse
10th International Congress on X-Ray Optics and Microanalysis

J. Phys. Colloques 45 (1984) C2-595-C2-598

DOI: 10.1051/jphyscol:19842139


G. Siegel1, A. Walter1 et B. Lindman2

1  Biophysical Research Group, Institute of Physiology, The Free University of Berlin, D-1000 Berlin 33, F.R.G.
2  Department of Physical Chemistry 1, Chemical Center, University of Lund, S-220 07 Lund, Sweden

Des variations de concentrations externes en protons et/ou en cations produisent des modifications des propriétés de liaison des macromolécules polyanioniques dans le tissu conjonctif vasculaire. Ainsi, la concentration extracellulaire des différentes espèces cationiques peut varier de façon rapide et importante dans les mailles du réseau conjonctif et au voisinage de la membrane des cellules vasculaires lisses. En particulier, l'adsorption potassique par acidification de la solution extracellulaire comme la liaison par coopération du potassium (consécutive aux changements conformationnels induits par les ions Mg2+ dans les polyanions) présentent une grande importance dans l'hyperpolarisation membranaire et la vasodilatation.

The pH-dependent binding of monovalent cations to vascular connective tissue is dependent on the concentration and affinity constant of the ion species in question. The mode of interaction is competition. Divalent cation binding to vascular connective tissue and its proteoglycans is additionally dependent on conformational changes. For example, competition experiments in physiological Krebs solutions using multi-chain chondroitin sulphate and Mg2+ at pH 7.38 showed increasing 23Na+ excess transverse relaxation rates during the initial phase [cf.5]. Above 4 mM Mg2+ simple exchange of bound Na+ with Mg2+ was observed. The increased excess transverse relaxation rate seen upon Mg2+ additions was referred to an increase in the correlation time. In the presence of Mg2+, cross-linking of chains, clustered together on the protein core, was promoted. Thus, physiological concentrations of Ma2+ ions can induce a specific change in the configuration of the anionic biopolymers, which enables K+ ions to bind cooperatively (nH = 6.8), while the adsorption of all the other cations is competitively inhibited. This means that with extracellular Mg2+ excess not only more Mg2+ ions are bound to vascular connective tissue but also more K+ ions. [K+]0 would decrease near the cell membrane, hyperpolarization and vasodilatation would occur.