Effect of medium tonicity on transepithelial H(+)‐HCO3‐fluxes in rat proximal tubule.

Abstract

SUMMARY1. The effect of luminal and capillary perfusion with hypotonic or hypertonic solutions containing 25 mm NaHC(3 or NaH2PO4 plus NaCl, K+, Ca2+, Mg2+ and acetate at an osmolalitv of 100 or 500 mosmol kg-1 on rat proximal ll+ secretion was estimated by monitoring luminal pH with Sb microelectrodes. The results were compared to perfusions with the same ionic concentration in which tonicity was adjusted to 300 mosinol kg-1 with raffinose.2. The kinetics of acidification of luminally injected bicarbonate buffer permits evaluations of H+-HCO3-fluxes as well as stationary pH gradients; the kinetics of alkalinization of luminally injected acid phosphate buffer indicates HI-HCO3-backfluxes from blood to lumen.3. In alkalinization experiments, luminal perfusion with hypotonic solution during presence of blood in capillaries or hypotonic capillary perfusion leads to a decrease of stationary pH. an increase of alkalinization half-time and consequently a decrease of passive H+-HCO3-backflux.4. In alkalinization experiments, during luminal and/or capillary perfusions with hypertonic solutions, no significant differences in the stationary pH, alkalinization half-time and H+-HC03-backflux were found.5. During acidification experiments, with both hypo and hypertonic perfusions: no significant differences in stationary pH, acidification half-time and H+-IHCO3 flux were observed.

Claudin‐2‐mediated cation and water transport share a common pore

“…For example, the TER value of claudin‐2‐expressing MDCK I cells (160 Ω cm 2 ) is much higher compared with the proximal tubules (4.5 Ω cm 2 (Melis et al . ) and 16 Ω cm 2 (Bello‐Reuss )).…”