The uptake mechanism of indocyanine green byrat isolated hepatocytes

The uptake mechanisms of indocyanine green (ICG) were studied with rat native hepatocytes and denatured ones which were treated at 56°C for 10 minutes. The addition of several receptor blockers except aggregated IgG to the reaction system was not able to impair the uptake. Although metabolic inhibitors had no affect on the uptake, it was drastically reduced at low temperature. The denatured hepatocytes also eliminated ICG from reaction system rapidly rather than the native cells and it was inhibited at low temperature. The kinetic analysis of the ICG uptake by double reciprocal plots of Lineweaver-Burk showed the 4.76 nmol/min/106 cells of Vmax value and 0.15 mM of Km value for native hepatocytes but the line of denatured cells crossed at the origin, i. e., no Vmax and Km value was given as thesimple chemical binding of ICG. Subcellular fractionation of both the native and denatured hepatocytes after incubation with ICG indicated that ICG was distributed from membrane to lysosomal fraction in native cells but the most ICG was found in the membrane fraction in the case of denatured cells. Thus the uptake by denatured hepatocytes was not true one but the binding of ICG to the cell.