Expresión de APXL in human placenta

DEL MÓNACO SILVANA; DAMIANO, ALICIA E; ZOTTA ELSA; IBARRA CRISTINA; KOTSIAS BASILIO

San Pablo

Simposio; I Latin-American Symposium on Maternal-Fetal Interaction and Placenta:Basic & Clinical Research; 2003

Placenta Association of the Americas- Grupo Latinoamericano de placenta

The syncytiotrophoblast is the outermost covering of the fetal placental villi and acts as a physiological barrier between mother and fetus blood. It controls transcellular movement of water and solutes helping to maintain a normal fetal growth and homeostasis. In our studies we have found that there are high amounts of a protein called APXL, (Apical Protein of Xenopus Like) in human placental syncytiotrophoblast. This protein was also detected in other human tissues (lung, pancreas and retina) although it is still unknown its physiological function. The name APXL comes from the homology with another protein, APX (Apical Protein of Xenopus), associated to an apical Na+ channel purified from A6 Xenopus laevis kidney cells. It has been suggested that APX represents a 9 pS channel regulated by the cytoskeleton, stimulated by vasopresin and PKA, and inhibited by amiloride. In order to study the function of APXL and its relation to Na+ placental transport we firstly confirmed its presence in human syncytiotrophoblast by RT-PCR, western blot and immunohistochemical analysis. The RT-PCR amplified fragment was cloned and sequenced, resulting in 100% homology with the sequence from retina reported by Schiaffino et al., (1995). We are currently screening a cDNA library from placenta to obtain the full APXL gene. As our project includes the expression of this protein in Bufo arenarum oocytes to perform voltage clamp and kinetic analysis, we proved the absence of APX and APXL in these oocytes by immunohistochemical analysis and the absence of amiloride sensitive currents by voltage clamp. We have also observed that the  subunit of the epithelial sodium channel ENaC is not present in the oocytes or in syncytiotrophoblast. These results confirm that the model is appropriate to complete our study.