Effects of neurosteroids on Ca(2+) signaling mediated by recombinant N-methyl-D-aspartate receptor expressed in Chinese hamster ovary cells.

Pregnenolone sulfate (PREGS) potentiates the N-methyl-D-aspartate (NMDA) receptor-mediated Ca(2+)-signals in cultured hippocampal neurons. The NMDA receptor family has several different subunits whose expression in neurons has distinct spatial and temporal patterns. To examine subunit specificity of the PREGS action, we have investigated the effect of PREGS on recombinant GluR epsilon2/zeta1 (NR2B/NR1) type NMDA receptors stabley expressed in Chinese hamster ovary cells using heat shock promoters. PREGS enhanced the Ca(2+) influx through the GluR epsilon2/zeta1 receptors in a dose-dependent manner. The EC(50) of PREGS for the GluR epsilon2/zeta1 receptors was 8.6 microM. Other sulfated neurosteroids, dehydroepiandrosterone sulfate (DHEAS), 17beta-estradiol sulfate and 3alpha-ol-5beta-pregnan-20-one sulfate (3alpha5betaS), inhibited the positive modulatory effect of PREGS on the GluR epsilon2/zeta1 NMDA receptors. Ifenprodil, a specific inhibitor of GluR epsilon2 subunit, abolished the NMDA-induced Ca(2+) influx even in the presence of PREGS. These results imply that PREGS positively modulates the Ca(2+) influx through the GluR epsilon2/zeta1 receptors which are expressed from the embryonic period.