Non-specific effects of the MEK inhibitors PD098,059 and U0126 on glutamate release from hippocampal synaptosomes.
In order to investigate a role for the extracellular-signal-regulated kinases 1 and 2 (ERK1/2) on hippocampal neurotransmitter release, we studied the effect of commonly used MEK (mitogen-activated protein kinase [MAPK]/ERK kinase) inhibitors, PD098,059 and U0126, on depolarization-induced glutamate release. PD098,059 inhibited glutamate release from hippocampal synaptosomes stimulated with 15 mM KCl in a concentration-dependent manner. At the same range of concentrations, PD098,059 inhibited basal and KCl-stimulated ERK1/2 phosphorylation. U0126, however, did not significantly affect KCl-evoked glutamate release at concentrations shown to inhibit ERK activity. Nonetheless, U0126 unspecifically potentiated depolarization-induced Ca2+-independent glutamate release, which masked a small dose-dependent inhibitory effect on the Ca2+-dependent release. PD098,059 reduced the [Ca2+]i response to KCl by partially inhibiting Ca2+ entry through N- and P-/Q-type voltage-gated Ca2+ channels, whereas U0126 did not affect depolarization-induced Ca2+ influx. To overcome the unspecific effect of PD098,059 on Ca2+ entry, we studied the effect of both MEK inhibitors on glutamate release stimulated by a Ca2+ ionophore. PD098,029 and U0126 showed a small dose-dependent inhibitory effect on ionomycin-induced glutamate release, at concentrations shown to inhibit ionomycin-stimulated ERK phosphorylation. These findings uncover new unspecific actions for both MEK inhibitors and suggest a minor role for ERK in modulating glutamate release in the hippocampus.
Pereira
D B
DB
Center for Neuroscience of Coimbra, University of Coimbra, 3004-517, Coimbra, Portugal.
Carvalho
A P
AP
Duarte
C B
CB
D000818:Animals; D002070:Butadienes / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005419:Flavonoids / Q000494:pharmacology*; D018698:Glutamic Acid / Q000378:metabolism*; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D015151:Immunoblotting; D066298:In Vitro Techniques; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors*; D009411:Nerve Endings / Q000187:drug effects / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*
D002070:Butadienes; D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007476:Ionophores; D009570:Nitriles; C113580:U 0126; D018698:Glutamic Acid; D015759:Ionomycin; D011189:Potassium Chloride; D020928:Mitogen-Activated Protein Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D002118:Calcium