Electrical resistance and ion diffusion through mesothelium

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Abstract

(1) Since phospholipids (PHL) added on the luminal side of specimens of parietal pericardium of rabbits decrease diffusional permeability (P) to Na+, but not to Cl, P to Rb+, a cation with hydrated radius similar to that of Cl was measured. PRb+ was 13.1 (±1.1, S.E.)×10−5 cm/sec and it was not decreased by PHL. This suggests that PHL decrease size of intercellular ‘pores’ of mesothelium, and restrict diffusion of solutes with radius>0.2 nm. (2) Electrical resistance (Re) of pericardium specimens was measured without PHL, with PHL, and after mesothelium was scraped away, to obtain Re of connective tissue and, thus, to compute Re of mesothelium. Re of connective tissue was 1.0±0.2 Ω cm2; Re of mesothelium was 10.1±0.6 and 12.3±0.9 Ω cm2 without and with PHL, respectively. The fraction of electrical current carried by Na+ indicates that Na+ diffusion through mesothelium without PHL is nearly free. (3) Re of cultured mesothelial cell monolayers of rat visceral pleura was 6.1±0.2 Ω cm2, i.e. smaller than that of specimen mesothelium; it did not increase with PHL. PNa+ of cultured mesothelial cell monolayers was 20.0×10−5 cm/sec, i.e. greater than that of specimen mesothelium.

Introduction

Pleural liquid is essential for the mechanical coupling between lung and chest wall: it ensures complete and instantaneous transmission of perpendicular forces between the two structures and sliding of the two pleural surfaces on each other in response to shearing forces. For this coupling to be effective, the thickness of the liquid layer must be kept to a minimum. Liquid is filtered into the pleural space through the parietal mesothelium by Starling forces, and is absorbed through the visceral mesothelium by Starling forces (Agostoni, 1972) and through the stomata of the parietal mesothelium by lymphatic drainage (Miserocchi, 1991). Recently, indirect evidence has suggested a third absorbing mechanism coupled to an active solute transport through the mesothelium (Agostoni and Zocchi, 1998). In order to understand more completely the exchanges of liquid and solutes of the pleural space, it is important to know the biophysical properties of the mesothelium and of the underlying connective tissue. Direct measurements on pleural specimens, however, generally appear unreliable because of the difficulty in avoiding severe damage of the mesothelium during sample collection. On the other hand, specimens of the retrosternal part of the parietal pericardium may be obtained with much less damage than those of the pleura (Zocchi et al., 1998), and the morphological features of the mesothelium are similar in pleura and pericardium (see Zocchi et al., 1998 for literature); moreover, this part of the pericardium should be essentially free of stomas (Takada et al., 1991). The diffusional permeability (P) of the parietal pericardium of rabbits to sucrose, mannitol, Na+, Cl and water has been recently determined (Zocchi et al., 1998, Agostoni et al., 1999). After having scraped away the mesothelium from the specimen, P of the connective tissue to the above solutes and to water has also been measured. Since the connective tissue and the mesothelium are placed in series, P of the mesothelium has been computed from P of intact and scraped specimens (Zocchi et al., 1998, Agostoni et al., 1999). P to the solutes was smaller in the mesothelium than in the connective tissue, though the latter is 35 times thicker, while P to water was greater in the mesothelium, suggesting a marked diffusion of water through mesothelial cell membrane. The addition of phospholipids to the solution facing the luminal side of the pericardium, where they should be adsorbed (Hills et al., 1982, Hills and Butler, 1985), markedly decreased P of the mesothelium to the small uncharged solutes (radius 0.44–0.52 nm) and to Na+ (hydrated radius 0.26 nm), but did not significantly decrease P to Cl (hydrated radius 0.19 nm) (Agostoni et al., 1999), though phospholipids should not be positively charged in the physiological range of pH (Bangham and Dawson, 1959).

The purposes of the present research are 3-fold. First, it was checked whether the hindrance to Na+ diffusion caused by phospholipids depends on a decrease in size of the intercellular ‘pores’ as suggested by Fig. 1 of Agostoni et al. (1999). To this end P of the pericardium to Rb+ was determined without and with phospholipids, because the hydrated radius of this cation (0.18 nm) is similar to that of hydrated Cl and, therefore, its diffusion should be little restricted by phospholipids, if the above hypothesis is correct. Second, in order to further the knowledge on the biophysical properties of the serosae, the electrical resistance of the mesothelium and of the connective tissue of the parietal pericardium was measured, because the only data available on this subject are indirect measurements done on the mesothelium and connective tissue of frog mesentery (Crone and Christensen, 1981). These measurements were repeated after the addition of phospholipids in order to ascertain whether phospholipids increase the resistance of the mesothelium in a way compatible with their different effect on the diffusion of Cl and Na+, which should carry most of the electrical current through the specimens. Third, because of lack of data on the biophysical features of cultured mesothelial cell monolayers (Jaurand et al., 1985), and in order to gain some information also on pleural mesothelium, the electrical resistance and P to Na+ of confluent monolayers of mesothelial cells from rat visceral pleura was measured.

Section snippets

Specimen collection and preparation

Specimens of parietal pericardium were obtained from 150 giant rabbits (body weight 5–7 kg, age 7–11 months). The animals were anesthetized with a solution containing sodium pentobarbital (Sigma, 10 mg/ml) and urethane (Sigma, 250 mg/ml), 2 ml/kg intravenously, and placed supine on a tilting board 20 deg head up. The trachea was cannulated to ensure adequate ventilation during the preliminary surgical procedure, and air flow and tidal volume were recorded on a 7418 Hewlett-Packard thermopaper

Results

The diffusional permeability to Rb+ (PRb+) of the parietal pericardium without and with the addition of phospholipids in the solution facing the luminal side is reported in Table 1. The addition of phospholipids did not produce a significant decrease of PRb+.

The electrical resistance (Re) and the thickness of the parietal pericardium of rabbits in the experiments without and with the addition of phospholipids are reported in Table 2. The addition of phospholipids increased Re of the pericardium

Discussion

The finding that the addition of phospholipids to the luminal side of the pericardium does not decrease PRb+, together with the previous one that this addition decreases markedly PNa+, but does not decrease significantly PCl (Agostoni et al., 1999), indicates that the hindrance to diffusion caused by phospholipids depends on a decrease in size of the intercellular ‘pores’. Since the values of the equivalent radius of hydrated Rb+, Cl and Na+ are 0.18, 0.19 and 0.26 nm, respectively, these

Acknowledgements

We are most grateful to Drs N. Cascinelli and E. Bombardieri (Istituto Nazionale per lo Studio e la Cura dei Tumori, Milano) for allowing us to use the facilities of the Divisione di Medicina Nucleare for part of the experiments. We thank Mr R. Galli for his skilful technical assistance during specimen collection. This research was supported by Ministero dell'Università e della Ricerca Scientifica e Tecnologica (MURST) of Italy.

References (36)

  • P.H. Barry et al.

    Effect of unstirred layers on membrane phenomena

    Physiol. Rev.

    (1984)
  • E.L. Boulpaep et al.

    Electrophysiology of proximal and distal tubules in the autoperfused dog kidney

    Am. J. Physiol.

    (1971)
  • C. Crone et al.

    Electrical resistance of a capillary endothelium

    J. Gen. Physiol.

    (1981)
  • F.E. Curry

    Determinants of capillary permeability, a review of mechanisms based on single capillary studies in the frog

    Circ. Res.

    (1986)
  • R.I. Freshney

    Culture of Animal Cells: A Manual of Basic Technique

    (1983)
  • R.A. Frizzell et al.

    Sodium chloride transport by rabbit gallbladder

    J. Gen. Physiol.

    (1975)
  • S. Glasstone

    Textbook of Physical Chemistry

    (1953)
  • F.R. Haselton et al.

    Chromatographic demonstration of reversible changes in endothelial permeability

    J. Appl. Physiol.

    (1989)
  • Cited by (0)

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