THE GRADIENT OF VASCULAR PERMEABILITY : II. THE CONDITIONS IN FROG AND CHICKEN MUSCLE, AND IN THE MAMMALIAN DIAPHRAGM

Claudin-5 controls intercellular barriers of human dermal microvascular but not human umbilical vein endothelial cells

OBJECTIVE

To assess the role claudin-5, an endothelial cell (EC) tight junction protein, plays in establishing basal permeability levels in humans by comparing claudin-5 expression levels in situ and analyzing junctional organization and function in 2 widely used models of cultured ECs, namely human dermal microvascular (HDM)ECs and human umbilical vein (HUV)ECs.

METHODS AND RESULTS

By immunofluorescence microscopy, ECs more highly express claudin-5 (but equivalently express vascular endothelial-cadherin) in human dermal capillaries versus postcapillary venules and in umbilical and coronary arteries versus veins, correlating with known segmental differences in tight junction frequencies and permeability barriers. Postconfluent cultured HDMECs express more claudin-5 (but equivalent vascular endothelial-cadherin) and show higher transendothelial electric resistance and lower macromolecular flux than similarly cultured HUVECs. HDMEC junctions are more complex by transmission electron microscopy and show more continuous claudin-5 immunofluorescence than HUVEC junctions. Calcium chelation or dominant negative vascular endothelial-cadherin overexpression decreases transendothelial electric resistance and disrupts junctions in HUVECs, but not in HDMECs. Claudin-5 overexpression in HUVECs fails to increase transendothelial electric resistance or claudin-5 continuity, whereas claudin-5 knockdown in HDMECs, but not in HUVECs, reduces transendothelial electric resistance and increases antibody accessibility to junctional proteins.

CONCLUSIONS

Claudin-5 expression and junctional organization control HDMEC and arteriolar-capillary paracellular barriers, whereas HUVEC and venular junctions use vascular endothelial-cadherin.

THE LYMPHATIC PARTICIPATION IN HUMAN CUTANEOUS PHENOMENA : A STUDY OF THE MINUTE LYMPHATICS OF THE LIVING SKIN

A technic is described for the demonstration of lymphatic capillaries in living skin and for their study. By means of vital dyes injected intradermally these vessels can be rendered plainly visible. They form an extraordinarily abundant anastomotic web. The least scratch, one which does not penetrate through the epidermis, gives rise to such conditions that lymphatic absorption readily takes place from the abraded surface; and so close-meshed is the lymphatic web that an intradermal injection with even the finest hypodermic needle tears some of the constituent vessels open with result that they undergo direct injection. In many individuals much of the fluid introduced at an ordinary intradermal injection, like that made in the clinic, spreads through the superficial lymphatic network, whereas in others it tends to enter the deeper lymphatics at once, the difference being due to merely physical factors determined by skin texture. Normal flow along the skin lymphatics is rapid even when the body is at rest, dye introduced into the skin of the resting forearm reaching the axilla within a few minutes. The observations make plain the fact that every intradermal injection is an intralymphatic one, often preponderantly such, while furthermore every local injection into the skin becomes within a few minutes a general one, so rapidly is the introduced material transported to the blood. The normal permeability of the skin lymphatics of man is approximately the same as that of the mouse. Tests indicate that in both instances the lymphatic wall behaves like a semipermeable membrane. The permeability of the human lymphatic wall like that of the mouse is subject to rapid and great changes. A stroke on the skin with a blunt instrument to produce a wheal, causes the lymphatic capillaries to become so permeable temporarily that dyes pass through their walls as if practically no barrier existed, instead of being held back for a greater or less period. Slight inflammation due to heat, ultraviolet light or bacterial products has a similar effect. So, too, has histamine. When fluid pours rapidly into the tissue from the blood, as when a wheal is formed, the lymphatics are compressed and their efficiency as drainage channels is interfered with. These facts are briefly discussed in their bearing upon skin phenomena in general. The lymphatics cannot be disregarded in considering such phenomena, in which it is plain that they have a large share.

THE GRADIENT OF PERMEABILITY OF THE SKIN VESSELS AS INFLUENCED BY HEAT, COLD, AND LIGHT

The mounting gradient of permeability along the small vessels of the corium is essentially unaltered by active hyperemia produced by heat, cold, or light. Only when the vascular walls are so damaged that rapid leakage ensues, as shown by the development of edema, does the permeability of the capillary web as a whole approximate that of the venules. It is plain that the normal gradient of vascular permeability depends upon the integrity of the vessel wall. The method of experiment described can be utilized for a study of the functional changes which result in the lesions due to burning and freezing.

THE GRADIENT OF VASCULAR PERMEABILITY : IV. THE PERMEABILITY OF THE CUTANEOUS VENULES AND ITS FUNCTIONAL SIGNIFICANCE

The permeability of the venules of the skin of the mouse greatly exceeds that of the capillaries. A mounting gradient of permeability exists along the further portion of the latter. The significance of these facts is discussed with relation to conditions in human skin. The cutaneous venules are differentiated for several functions besides those ordinarily attributed to them, and must be considered as specialized organs.

THE GRADIENT OF VASCULAR PERMEABILITY : III. THE GRADIENT ALONG THE CAPILLARIES AND VENULES OF FROG SKIN

A steeply mounting gradient of permeability is demonstrable along the meshwork of capillaries which connects the arterioles and venules of the skin of the frog. The venules incorporated in the meshwork are even more permeable than the capillary meshes giving into them. The presence of the gradient under such differing conditions as exist along frog and mammalian capillaries enables one to rule out certain factors which might be invoked to explain it; and it is not explainable in terms of those influences generally recognized as conditioning exchange between the blood and tissues. Not improbably it results from a structural differentiation along the capillary.

THE RELATION OF HYDROSTATIC PRESSURE TO THE GRADIENT OF CAPILLARY PERMEABILITY

The gradient of permeability along the capillaries of voluntary muscle and the capillaries and venules of skin exists independently of the hydrostatic conditions, though influenced by them. Its presence cannot be explained by a graded tonic contraction of the capillaries. The evidence,—like that of previous papers,—points to local differences in the barrier offered by the wall of these vessels as responsible for the gradient.

Surgical exposure induces formation of an arteriovenous permeability gradient for macromolecules in the microcirculation of muscle

Rous and his colleagues (P. Rous, H. P. Gilding, and F. Smith, 1930, J. Exp. Med. 51, 807-830, F. Smith and P. Rous, 1931, J. Exp. Med. 53, 195-217) uncovered evidence for an arteriovenous gradient of permeability in exchange vessels of muscle. After injecting vital dyes intravenously in laboratory animals, including mice and rats, they examined escape of the dyes from exchange vessels of abdominal muscles, prepared for observation by reflection of the overlying skin. They noted that a particular class of dyes, termed "poorly diffusible," escapes from venules but not from arterioles and capillaries a few minutes after injection. We now assume that the "poor" diffusibility of the dyes stems from their binding to plasma proteins. We repeated similar experiments in mice and rats, using Evans blue as tracer, and also observed leakage of Evans blue from venules but not from other exchange vessels. We made three additional observations. (1) Evans blue leaks from venules only after the skin overlying the abdominal muscles is reflected. (2) Reflection of the skin initiates degranulation of mast cells in the muscles. (3) Leakage of Evans blue from venules is inhibited by administration of promethazine, a histamine and serotonin antagonist, to the animals prior to reflection of the skin. On the basis of our observations, we conclude that the arteriovenous permeability gradient for poorly diffusible dyes in the microcirculation of muscle represents response to tissue injury resulting from reflection of overlying skin.