Studies of the capillary basal lamina. I. Ultrastructure of the red body of the eel swimbladder.

The rete mirabile of the eel swimbladder is a vascular organ in which arterial andvenous capillaries alternate in regular fashion. The endothelium of the arterial capillaries is high, whereas that of the venous capillaries is thin and fenestrated. Endothelial cells and pericytes are the only cells found in the rete. A tubular systemin the arterial endothelial cells is connected with the organelles. The basal laminaeof both capillaries are similiar to those of mammalian capillaries of the same type. They present three layers of different electron density and have a high fibrillar pattern.A fine fibrillar material and dense fibrils appear in the cisternae of the rough endoplasmic reticulum and in large vacuoles of endothelial cells and pericytes: these cells areapparently involved in the synthesis of their lamina. Since the rete mirable ofthe eel swimbladder is a pure vascular preparation, it is most useful for the study of themorphology, the permeability, and the metabolism of the endothelial cells and for the analysis of the chemical structure of their basil laminae.