Radioactive gold colloid as a tracer of macromolecule transport 1

Abstract

A tracer system suitable for radioisotope, autoradiographic or electron microscopic investigations of macromolecule transport in tissues is described. The tracer consists of an electron dense nucleus of radioactive colloidal gold stabilised by a macromolecular coating into which a second radioactive label may be incorporated. The physical characteristics of the tracer system have been investigated. Commercially produced gelatin coated particles suspended in 0.9% NaCl had total hydrodynamic radii ranging between 70 Å and 200 Å and nuclear radii of between 15 and 25 Å. Particles of a single hydrodynamic radius showed similar electrophoretic mobility but had a wide range of iso- electric points. Incubation in plasma produced an increase in the hydrodynamic radius of the particles. The rate of adsorption increased with the initial radius of the particles and with the temperature of incubation. From the temperature dependence an activation energy for the adsorption process of 46 ± 6 k Joule mole⁻¹ was deduced. Incubation with serum or with fibronectin produced a smaller increase in particle size, but incubation with fibrinogen, albumin or γ-globulin, alone or in combination in either 0.9% NaCl or Tyrode’s solution, had no effect on particle size.