Progesterone increases the activity of the rat glutamate transporter type 3 expressed in Xenopus oocytes

Abstract

Background : Progesterone is an important sex hormone for pregnancy and also has neuroprotective and antiepileptic effects as a neurosteroid hormone. It is well known that minimum alveolar concentration (MAC) of inhalation anesthetics is reduced during pregnancy. Glutamate transporters are important for preventing neurotoxicity and for anesthetic action in the central nervous system. The author investigated the effects of progesterone on the activity of glutamate transporter type 3 (EAAT3). Methods : EAAT3 was expressed in Xenopus oocytes by injecting its mRNA. Oocytes were incubated with diluted progesterone for 72 hours. Two-electrode voltage clamping was used to measure membrane currents before, during, and after applying L-glutamate (30 μM). Responses were quantified by integrating the current traces and reported in microCoulombs (μC). Results are presented as mean±S.E.M. Results : Progesterone concentration from 1 to 100 nM significantly increased the responses in a dose-dependent manner. Kinetic study showed that Vmax was increased compared with control group (2.7±0.2 μC for control group vs. 3.6±0.2 μC for progesterone group; n=13-16; p<0.05), but Km was not changed (46.7±10.2 μM for control group vs. 55.9±10.5 μM for progesterone group; n=13-16; p>0.05). Phorbol-12-myristate-13-acetate (PMA), a protein kinase C (PKC) activator did not change progesterone-induced EAAT3 activity. Staurosporine, a protein kinase C inhibitor and wortmannin, phosphatidylinositol 3-kinase (PI3K) inhibitor abolished the progesterone-induced increases of EAAT3 activity. Conclusions : Our results suggest that progesterone increases the EAAT3 activity and that PKC and PI3K may mediate this effect. These effects of progesterone may explain its neuroactive and anesthesia-related properties.