Mechanisms of ion transport across the choroid plexus

Abstract

SUMMARY1. Mechanisms of ion transport across the choroidal epithelium were investigated using an in vitro preparation of the frog choroid plexus.2. Sodium was actively transported across the plexus from the vascular to the ventricular surface by an ouabain sensitive electrically silent pump. As in other epithelial membranes the rate of sodium transport was stimulated by the presence of bicarbonate ions in the Ringer solutions. Chloride and bicarbonate ions accompany the net flux of sodium across this tissue. 3. Some experiments suggest that potassium is actively transported from the ventricular to the serosal surface, and that the rate of transport is a function of the extracellular potassium concentration.4. No evidence was obtained to suggest that calcium is actively transported across this tissue in either direction.5. Diamox, ethoxyzolamide, pitocin, pitressin, hydrocortisone, amiloride, spironolactone and anoxia all failed to influence sodium transport.6. The sequence of passive ion permeation across the plexus was PRb K-P > PCs PNa PC, -PHCO1 > PLI as deduced from diffusion potential measurements. At least for Na, K and Cl there was a good correlation between the permeability coefficients derived from unidirectional flux measurements and from electrical parameters. This indicates that exchange diffusion is unimportant as a mechanism for passive ion transport. 7. The instantaneous current-voltage curves were linear in both symmetrical and asymmetrical salt solutions and the choroid plexus conductance was found to be directly proportional to the external salt concentration. These and other lines of evidence suggest that the major route of passive ion permeation across this epithelium is via the tight junction route and not through the cell interior.8. These results are discussed in relation to the in vivo studies of c.s.f. secretion and the mechanisms of active and passive ion transport across other epithelial membranes such as the gall-bladder, intestine and renal proximal tubule.

Specific Ouabain Binding to Brain Microvessels and Choroid Plexus

“…cerebrospinal fluid formation by the choroid plexus (Wright , 1972). Ouabain-sensitive Rb + uptake by isolated cerebral microvessels has been demon strated in vitro (Eisenberg and Suddith, 1979;Gold stein , 1979;Chaplin et aI.…”

The formation of cerebrospinal fluid: Nearly a hundred years of interpretations and misinterpretations

“…Experimental results (Di Chiro, 1964;Orešković et al, 1991;Sato et al, 1972;Sato et al, 1971;Sato and Bering, 1967) also show that CSF is formed outside the brain ventricles (in subarachnoid space). The results also show that CSF absorption occurs not only through villi arachnoidales, but also inside the brain ventricles (Brightman, 1968;Bulat et al, 2008;Cserr, 1971;Dodge and Fishman, 1970;Foley, 1921;Hassin, 1924;Orešković et al, 1991;Wright, 1972), along the nerve roots (Kido et al, 1976), from the subarachnoid space into the lymphatic system (Bradbury, 1981;Brierly and Field, 1948;Dandy, 1929;Johnston et al, 2005;Johnston et al, 2004;Koh et al, 2005;Koh et al, 2006;Weed, 1914), and high intraspinal absorption (Edsbagge et al, 2004).…”

“…Based on all of this, it can be presumed that (in terms of evolution) by bringing the blood vessels in close contact (immersing into) with CSF this could accomplish a significant and fast exchange of matter between the blood and the CSF, and vice versa, with the purpose of supporting the maintenance of the biochemical balance of the CSF as an important physiological medium for normal CNS functioning. This theory is also supported by a rather old idea that the choroid plexuses (undoubtedly a secretory active tissue) participate in CSF absorption in a manner of two way traffic (Brightman, 1968;Cserr, 1971;Dodge and Fishman, 1970;Foley, 1921;Hassin, 1924;Wright, 1972). After all, it could be said that everything that has been discussed calls for a new approach and hypothesis of CSF hydrodynamics.…”

“…The rate of CSF formation has been measured in turtles, rats, sharks, rabbits, cats, monkeys, dogs, goats, and calves at approximately 1.4; 2.2; 3-4; 8-11; 14-21; 19-35; 35-50; 160; 290 µl/min, respectively (Cserr, 1971;Heisey et al, 1962;Milhorat, 1989;Orešković et al, 2000;Rennels et al, 1990;Wright, 1972). The rate of CSF formation in humans is about 0.3-0.4 ml/min (Cutler et al, 1968;Masserman, 1934;Pollay, 1972;Rubin et al, 1966;11 Sjöqvist, 1937), which means that the total production per day is about 430-580 ml.…”

Binding Sites for Immune Components in Human Choroid Plexus

“…Like the cells of the proximal renal tubule, the choroidal epithelium has apical brush borders and is joined by apical zonulae occludentes which are restrictive to the passage of larger molecules (13). These cells contain NA-K ATPase and carbonic anhydrase and they can concentrate certain organic anions, acids and bases, monosaccarides, neutral amino acids, and purines (14,15). Significant numbers of macrophages, Kolmer cells, are present on the ventricular surface of the epithelium.…”