Transfer of Cl- across placenta of anesthetized rat

The mechanisms of Cl- transfer across the rat placenta have been investigated. Clearance across the intact placenta from mother to fetus (m-->f) of 51Cr-EDTA (paracellular diffusion marker) and 36Cl- (Kmf) was 1.9 +/- 0.1 and 37.3 +/- 4.1 microliters/min, respectively (mean +/- SE, n = 10), the large difference indicating that most m-->f transfer of Cl- is transcellular. The clearance of 36Cl- across the dually perfused placenta in m-->f and fetal-to-maternal directions was symmetrical and highly sensitive to the anion-exchange inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (0.1 mM). The Kmf of 36Cl- was not inhibited by anoxia and had a low temperature quotient (Q10 between 32 and 37 degrees C was 1.52). The m --> f transfer of Cl- seemed to be fully saturated at physiological concentrations of Cl-. 36Cl- could be displaced from the transporter on the maternal side by other anions with the following order of affinity: Cl- approximately NO3- > Br- > lactate- >> gluconate. It is concluded that most of the Cl- transfer across the rat placenta is effected by an anion exchanger.