Anion efflux from cytotrophoblast cells derived from normal term human placenta is stimulated by hyposmotic challenge and extracellular A23187 but not by membrane-soluble cAMP

The regulation of placental anion transport influences fetal accretion and placental homeostasis. We investigated whether efflux of I-125(-) or Cl-36( -) from multinucleated cytotrophoblast cells derived from human term placen ta is regulated by one of three stimuli: (a) the calcium ionophore A23187, (b) a 'cocktail' of agents designed to raise intracellular levels of cAMP, (c) a hyposmotic solution. After loading with the appropriate isotope for 2 h and thorough washing, cells were exposed to sequential aliquots of buffe r applied and removed each minute. Following an equilibration period of 5 m in one of the stimuli was applied at room temperature At the end of the exp eriment the cells were lysed to give a lysate count which was used to expre ss the count obtained from each aliquot as percentage efflux of that possib le for that minute. The cAMP 'cocktail' and A23187 were applied for 5 min; the hyposmotic solution was applied for 10 min. The results for I-125(-) at 7 min showed that the mean efflux in the presence of hyposmotic shock was greater than control (5.7 +/- 1.0% min(-1) versus 2.2 +/- 0.1% min(-1), res pectively; mean +/- S.E.M., n = 4 placentas). Similarly mean efflux at 6 mi n in the presence of A23187 was also significantly greater than control (6. 5 +/- 1.9% min(-1) versus 2.6 +/- 10 % min(-1), respectively, n = 3 placent as). The mean efflux in the presence of the cAMP cocktail was not different from control at any time point. The results were qualitatively the same if Cl-36(-) was used in the place of I-125(-) and when the experiment was per formed with Cl-36(-) in a HCO3- buffer gassed with CO2. Mean I-125(-) efflu x at 6 min in response to hyposmotic challenge was 33% less (P < 0.01) in t he presence of 1 mM 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DI DS) and 37% less (P < 0.005) in the presence of 10 mu M tamoxifen but no di fferent if the hyposmotic solution was nominally calcium free. We conclude that there are differential effects of second messengers on anion efflux fr om the differentiated cytotrophoblast cells.