ACTIVITY AND PROTEIN LOCALIZATION OF MULTIPLE GLUTAMATE TRANSPORTERS IN GESTATION DAY 14 VS. DAY 20 RAT PLACENTA

Concentrative absorption of glutamate by the developing placenta is cr itical for proper fetal development. The expression of GLAST1, GLT1, E AAC1, and EAAT4, known to be capable of D-aspartate-inhibitable and Na +-coupled glutamate transport (system X-AG(-)), was evaluated in day 1 4 vs. day 20 rat chorioallantoic placenta. Steady-state mRNA levels we re greater at day 20 for all transporters. Immunohistochemistry determ ined that the expression of GLAST1, GLT1, and EAAC1 was greater throug hout the day 20 placenta and was asymmetric with respect to cellular l ocalization. EAAT4 protein was not detected. System X-AG(-) activity w as responsible for most of the Na+-dependent glutamate uptake and was greater in day 20 than in day 14 apical and basal membrane subdomains of the labyrinth syncytiotrophoblast. Greater quantities of EAAC1 and GLAST1 protein were identified on day 20, and quantities were greater in basal than in apical membranes. GLT1 expression, unchanged in apica l membranes, was decreased in basal membranes. These data correlate tr ansporter mRNA and protein content with transport activity and demonst rate an increasing capacity for glutamate absorption by the developing placenta.