Water handling in the rat jejunum: effects of acidification of the medium

CAPURRO, CLAUDIA; PARISI, MARIO

PFLUGERS ARCHIV-EUROPEAN JOURNAL OF PHYSIOLOGY

SPRINGER

Año: 1992 vol. 421 p. 17 - 21

0031-6768

The minute-by-minute net water movement (Jw)in the rat jejunum was studied in relation to the diffusivewater (Pw) and mannitol (Ps) permeabilities with the followingresults. (a) Jw was a linear function of the appliedhydrostatic and osmotic transepithelial gradients (hydrostaticpermeability coefficient, Phydr = 0.052 + 0.01/cms- 1 ; osmotic permeability coefficient, Posm =0.0069 _+ 0.0014 cm s-1. (b) A fraction of this absorptiveJw (transport-associated Jw, Jwt = 0.086 _+ 0.024 glmin-a cm -2) was independent of the presence of anyosmotic, hydrostatic or chemical gradient. (c) In the absenceof Na +, Jwt was not significantly different fromzero and there was an increase in Phrdr but no change inPosm. (d) In the presence of a hydrostatic gradient (10 cmH20, mucosal side), acidification of the medium (95%CO2 bubbling, pH 6.2) simultaneously and reversibly increasedJw and decreased Pw. (e) When an osmotic gradientwas present (40 mM polyethyleneglycol on the serosalside) a net increase in Jw was observed. CO2 bubbling inthese conditions reversibly reduced Jw while increasingPs. (f) These effects were not observed when the serosalor mucosal pH was reduced in the presence of a nonpermeantbuffer (HEPES/TRIS; MES/TRIS). If we acceptthat Ps is a good marker of paracellular movementsand that Pw mainly reflects transcellular water movements,we may conclude that acidification of the medium,in the presence of bicarbonate, modifies both paracellularand transcellular routes. The experimental evidence indicatesthat an increase in proton concentration opens theparacellular pathway and probably has a blocking effecton a transcellular route.