Distribution of insulin receptors in liver cell suspensions using a minibead probe. Highest density is on endothelial cell.

The distribution of insulin receptors was studied in rat liver cell suspensions using a latex minibead covalently bound to insulin. This probe can be visualized by electron microscopy (EM). Using this visual probe, the highest density of the receptor was found on endothelial cells in the cell suspension, with hepatocytes having only few receptors and Kupffer cells having none. Fractionation of liver cell suspensions on metrizamide gradients yielded two populations of cells; large cells (hepatocytes) and small cells which consisted mostly of Kupffer cells and endothelial cells, distinguishable by their surface and cytoplasmic features. Again, by the use of an insulin-minibead probe, the highest density of receptors was found on endothelial cells. It is suggested that the endothelium has a crucial role in the uptake and transport of the hormone across the tissue-blood barrier.