Prostaglandin E(2) (
PGE(2)) is quantitatively one of the major
prostaglandins synthesized in mammalian brain, and there is evidence that it facilitates
seizures and neuronal death. However, little is known about the molecular mechanisms involved in such excitatory effects. Na(+),K(+)-
ATPase is a
membrane protein which plays a key role in
electrolyte homeostasis maintenance and, therefore, regulates neuronal excitability. In this study, we tested the hypothesis that
PGE(2) decreases Na(+),K(+)-
ATPase activity, in order to shed some light on the mechanisms underlying the excitatory action of
PGE(2). Na(+),K(+)-
ATPase activity was determined by assessing
ouabain-sensitive
ATP hydrolysis. We found that incubation of adult rat hippocampal slices with
PGE(2) (0.1-10 microM) for 30 min decreased Na(+),K(+)-
ATPase activity in a concentration-dependent manner. However,
PGE(2) did not alter Na(+),K(+)-
ATPase activity if added to hippocampal homogenates. The inhibitory effect of
PGE(2) on Na(+),K(+)-
ATPase activity was not related to a decrease in the total or plasma membrane immunocontent of the catalytic alpha subunit of Na(+),K(+)-
ATPase. We found that the inhibitory effect of
PGE(2) (1 microM) on Na(+),K(+)-
ATPase activity was receptor-mediated, as incubation with selective antagonists for EP1 (SC-19220, 10 microM), EP3 (L-826266, 1 microM) or EP4 (
L-161982, 1 microM) receptors prevented the PGE(2)-induced decrease of Na(+),K(+)-
ATPase activity. On the other hand, incubation with the selective EP2 agonist (
butaprost, 0.1-10 microM) increased
enzyme activity per se in a concentration-dependent manner, but did not prevent the inhibitory effect of
PGE(2). Incubation with a
protein kinase A (
PKA) inhibitor (
H-89, 1 microM) and a
protein kinase C (PKC) inhibitor (
GF-109203X, 300 nM) also prevented PGE(2)-induced decrease of Na(+),K(+)-
ATPase activity. Accordingly,
PGE(2) increased phosphorylation of Ser943 at the alpha subunit, a critical residue for regulation of
enzyme activity. Importantly, we also found that
PGE(2) decreases Na(+),K(+)-
ATPase activity in vivo. The results presented here imply Na(+),K(+)-
ATPase as a target for PGE(2)-mediated signaling, which may underlie PGE(2)-induced increase of brain excitability.