Occurrence of Unique Colloidal Particles in Snake Blood and their Transport across the Capillary Wall

A Proposal of a New Hypothesis on the Permeability of the Blood Capillaries

Abstract

Previously underscribed colloidal particles were found under the electron microscope in one-third of 65 individuals of the snake, Elaphe quadrivirgata. They were electron dense, spheroid bodies of a uniform size (20mμ in diameter) and were mainly located in the blood plasma and in the perivascular connective tissue space throughout the whole body.
In the capillary wall they were found within intracytoplasmic vesicular structures of the endothelium, subendothelial space and in the basement membrane. These findings were interpreted to indicate their transport across the capillary wall.
The colloidal particles, though similar in size to some of the tracers used in the previous studies of vascular permeability, essentially differed from them in that they comprised a physiological component of the blood plasma.
In the present material, not only fenestrae but also chains of two or more vesicles perforated the endothelium completely. Diaphragms similar to those of capillary fenestrae were also found at the orifices of caveolae and at the junctions of two vesicles. The diaphragms either in fenestrae, caveolae or between vesicles inhibited the passage of the particles. They were postulated to contain the structural equivalent of the “small pore system” proposed by some physiologists and it was supposed that the so-called “transport in quanta” might be less efficient, at least in this animal, than the outflow of substances through the fenestrae and channels tunneling through the endothelium. This mechanism of substance transport proposed in the present study may be called transport in continuum.
The basement membrane of the renal glomerular capillaries completely stemmed the colloidal particles, though this membrane of other capillaries was permeable to them.