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

Abstract

The regulation of placental anion transport influences fetal accretion and placental homeostasis. We investigated whether efflux of lZ5I-or 36Cl-from multinucleated cytotrophoblast cells derived from human term placenta is regulated by one of three stimuli: (a) the calcium ionophore A23 187, (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 buffer applied and removed each minute. Following an equilibration period of 5 min one of the stimuli was applied at room temperature At the end of the experiment the cells were lysed to give a lysate count which was used to express the count obtained from each aliquot as percentage efflux of that possible for that minute. The cAMP 'cocktail' and A23 187 were applied for 5 min; the hyposmotic solution was applied for 10 min. The results for lz5I-at 7 min showed that the mean efflux in the presence of hyposmotic shock was greater than control (5.7 _+ 1.0 % min-' versus 2.2 0.1 % min-', respectively; mean _+ s.E.M., n = 4 placentas). Similarly mean efflux at 6 min in the presence of A23187 was also significantly greater than control (6.5 f 1.9 % min-' versus 2.6 f 1.0% min-', respectively, n = 3 placentas). 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 36Cl-was used in the place of lz5I-and when the experiment was performed with 36Cl-in a HCO; buffer gassed with CO,. Mean lZ5I-efflux at 6 min in response to hyposmotic challenge was 33 % less ( P c 0.01) in the presence of 1 mM 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and 37 % less (P < 0.005) in the presence of 10 p~ tamoxifen but no diferent if the hyposmotic solution was nominally calcium free. We conclude that there are differenlial effects of second messengers on anion efflux from the differentiated cytotrophoblast cells.

Expression of Na+/I−Symporter and Pendred Syndrome Genes in Trophoblast Cells1

“…Pendrin acts as a sodium-independent transporter of chloride and iodide (12,15,25). Its location in the syncytiotrophoblast cells is compatible with several observations demonstrating that these cells control anion efflux, particularly I Ϫ and Cl Ϫ (26). The increase in PDS gene expression during gestation is in agreement with a marked maternal to fetal gradient of iodide through the villous syncytiotrophoblast layer during the second and third trimesters (1,2).…”

Purinergic receptors in human placenta: evidence for functionally active P2X4, P2X7, P2Y2, and P2Y6

“…For example, placental trophoblast cells express Ca 2ϩ -activated Cl Ϫ channels (27,59), and Cl Ϫ efflux could accompany K ϩ loss following purinergic receptor activation; this would also be expected to result in cell shrinkage. A role for ATP and UTP (via P2X and P2Y receptors) in modifying Cl Ϫ secretion has been shown in various epithelial cell types (56,57).…”

ATP-stimulated Ca2+-activated K+ efflux pathway and differentiation of human placental cytotrophoblast cells

“…However, efflux experiments under parallel conditions showed that substantial 86 Rb efflux, inhibited by charybdotoxin, still occurred. One possible explanation of this paradox arises from the fact that the EC 50 for Ca 2ϩ activation of IK is very low [95-320 nM (21, 24)]. Both studies proposed that activity of this channel would be expected to occur in unstimulated cells, and thus even a marginal increase in [Ca 2ϩ ] i , which might be barely detectable, may be sufficient to activate such an efflux pathway.…”

“…A Ca 2ϩ -activated Cl Ϫ current and a volume-activated Cl Ϫ current were also identified in these cells (28), as well as a volume-stimulated Ca 2ϩ -activated Cl Ϫ efflux pathway (50). Regulation of cation conductances is less well defined.…”