Abstract
Among the unsolved mysteries of modern biology is the nature of a lining of blood vessels called the 'endothelial surface layer' or ESL. In venous micro-vessels, it is half a micron in thickness. The ESL is 10 times thicker than the endothelial glycocalyx (eGC) at its base, has been presumed to be comprised mainly of water, yet is rigid enough to exclude red blood cells. How is this possible? Developments in physical chemistry suggest that the venous ESL is actually comprised of nanobubbles of CO2, generated from tissue metabolism, in a foam nucleated in the eGC. For arteries, the ESL is dominated by nanobubbles of O2 and N2 from inspired air. The bubbles of the foam are separated and stabilized by thin layers of serum electrolyte and proteins, and a palisade of charged polymer strands of the eGC. The ESL seems to be a respiratory organ contiguous with the flowing blood, an extension of, and a 'lung' in miniature. This interpretation may have far-reaching consequences for physiology.
Highlights
We understand a lot about molecular events inside cells, about nuclear DNA, our grasp of phenomena occurring at the surface of cells and of collections of cells is much less sure
Blood vessels are lined by a very unusual entity which was assumed to be part solid and part liquid, which acts as a cohesive unit, and is known as the endothelial surface layer or ESL (Pries et al, 2000)
With the analogy provided by what we know of lung surfactant structure, we might reasonably postulate that the ESL is comprised predominately of CO2 and O2 and O2/N2 nanobubbles in a stable foam
Summary
We understand a lot about molecular events inside cells, about nuclear DNA, our grasp of phenomena occurring at the surface of cells and of collections of cells is much less sure. Nanobubble model for the endothelial surface layer: a bicontinuous web of polysaccharide strands, water, salt and bubbles held together in a stable foam
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