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Am J Physiol Gastrointest Liver Physiol 260: G887-G894, 1991;
0193-1857/91 $5.00
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AJP - Gastrointestinal and Liver Physiology, Vol 260, Issue 6 887-G894, Copyright © 1991 by American Physiological Society

ARTICLES

Bicarbonate-induced activation of taurocholate transport across the basal plasma membrane of human term trophoblast

M. Y. el-Mir, N. Eleno, M. A. Serrano, P. Bravo and J. J. Marin
Department of Physiology and Pharmacology, University of Salamanca, Spain.

The efflux of [14C]taurocholate from previously loaded vesicles, obtained from basal plasma membrane of human trophoblast, was studied. Apparent Km (620 microM) and Vmax (1.79 nmol.min-1.mg protein-1) values were similar to those found in influx experiments (Marin et al., Gastroenterology 99: 1431-1438, 1990). Transmembrane gradients of both bicarbonate (100 mM) and unlabeled taurocholate (0.5 mM) accelerated [14C]taurocholate efflux. The bicarbonate-induced effect was not abolished by carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) and K(+)-valinomycin voltage clamp. Neither was it mimicked by 5,5'-dimethyloxazolidine 2,4-dione (DMO) or by other organic (taurine, glycine, lactate, or acetate) or inorganic (Cl-, SCN-, HPO24-, or SO24-) anions, and it was not sensitive to carbonic anhydrase inhibitors. No effect of bicarbonate was observed either in the absence of gradient or in the presence of a cis-directed gradient. Bicarbonate-induced transstimulation was related to an increase in the value for the apparent Vmax (+30%). Study of the stoichiometry suggests that the most probable coupling ratio is one, bicarbonate: taurocholate. In summary, these results provide evidence for the existence of a bicarbonate-driven anion exchange in the basal plasma membrane of the human term placental trophoblast.


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M. V. St-Pierre, M. A. Serrano, R. I. R. Macias, U. Dubs, M. Hoechli, U. Lauper, P. J. Meier, and J. J. G. Marin
Expression of members of the multidrug resistance protein family in human term placenta
Am J Physiol Regulatory Integrative Comp Physiol, October 1, 2000; 279(4): R1495 - R1503.
[Abstract] [Full Text] [PDF]


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