Evidence that prostaglandin E2 can block calcium-activated 86Rb efflux from rat brain synaptosomes via a protein kinase C-dependent mechanism

Modulation of glutamate-induced outward current by prostaglandin E(2) in rat dissociated preoptic neurons

The preoptic/anterior hypothalamus (POA) is one of the major brain regions where cytokines and their related mediators (i.e., prostaglandins) exert diverse actions. In the present study, the modulatory effects of prostaglandin E(2) (PGE(2)) on the glutamate-induced membrane currents were examined using perforated-patch clamp method in rat POA neurons that had been mechanically dissociated by vibration without enzyme treatment. Application of glutamate through U-tube induced a slow outward current following fast inward ionotroic current at a holding membrane potential of -30 mV. The slow outward current was also induced by N-methyl-d-aspartate (NMDA), accompanied by an increased membrane conductance, and inhibited by perfusion with Ca(2+)-free solution, tetraethylammonium chloride (TEA), and apamin, suggesting a Ca(2+)-dependent K(+) current (KCa) activated by Ca(2+) entry through NMDA channels. Perfusion with PGE(2) at 0.1-10 microM, a principal mediator of fever and neuroendocrine control at the POA, did not produce apparent current by itself, but selectively potentiated the glutamate- or NMDA-induced KCa without affecting inward currents. The KCa induced by activation of NMDA receptors may serve as a feedback mechanism and the modulatory effects of PGE(2) on the KCa may have an important physiological significance.

Prostaglandin E2 modulates a non-inactivating potassium current in rat neurohypophyseal nerve terminals

A non-inactivating voltage dependent K+ channel current was observed in neuro-hypophyseal nerve terminals. This current was sensitive to inhibition by 4-aminopyridine and tetraethyl ammonium chloride, but was not sensitive to inhibition by alpha- or beta-dendrotoxin. Prostaglandin E2 (PGE2) modulated the voltage-dependent K+ channel, through a receptor-mediated process, as indicated by meclofenamate sensitivity, and this involved the activation of G protein(s), as indicated by sensitivity to guanosine-5'-O-(2-thiodiphosphate) (GDPfS). After short periods of incubation (e.g. 5 min), PGE2 increased the non-inactivating current. Following longer incubation periods with PGE2 (e.g. 20 min), the non-inactivating current declined. Forskolin and the cyclic adenosine monophosphate (AMP) analogs 8-bromo- and dibutyryl cyclic AMP, and Sp-cyclic AMPs inhibited the current, but did not mimic the increase in current caused by PGE2. Also, the cyclic AMP antagonist Rp-cyclic AMPs did not block the increase in current induced by PGE2. These results indicate that activation of cyclic AMP-dependent protein kinase (PKA) is not involved in mediating the stimulatory actions of PGE2. These observations provide evidence that PGE2 may contribute to the regulation of hormone release from the posterior pituitary by modulating K+ channels. However, the post-receptor mechanisms of subcellular signal transduction underlying this effect remain unknown.

Comparative study of prostaglandin E2 production in chick spinal cord and meninges

In chick spinal cord the presence of low affinity (KD = 2.2 microM) receptors for prostaglandin E2 (PGE2) raises the question whether spinal cord possesses a PGE2 biosynthetic capacity able to activate these receptors. The production of PGE2 in spinal cord and meninges was investigated by enzyme immunoassay. Spinal cord exhibited a 30- to 100-fold lower PGE2 biosynthetic capacity compared to meninges, but can generate PGE2 resulting in micromolar concentrations, sufficient to activate the low affinity PGE2 receptors. It is suggested that in physiological conditions, PGE2 synthesized within the spinal cord might locally activate the low affinity PGE2 receptors, whereas in pathological situations, after disruption of the blood-spinal cord barrier, PGE2 produced by the meninges might be accessible to spinal cord PGE2 receptors, and thus largely contribute to their saturation.