title: CB1 receptors diminish both Ca(2+) influx and glutamate release through two different mechanisms active in distinct populations of cerebrocortical nerve terminals.
abstract: We have investigated the mechanisms by which activation of cannabinoid receptors reduces glutamate release from cerebrocortical nerve terminals. Glutamate release evoked by depolarization of nerve terminals with high KCl (30 mmol/L) involves N and P/Q type Ca(2+)channel activation. However, this release of glutamate is independent of Na(+) or K(+) channel activation as it was unaffected by blockers of these channels (tetrodotoxin -TTX- or tetraethylammonium TEA). Under these conditions in which only Ca(2+) channels contribute to pre-synaptic activity, the activation of cannabinoid receptors with WIN55,212-2 moderately reduced glutamate release (26.4 +/- 1.2%) by a mechanism that in this in vitro model is resistant to TTX and consistent with the inhibition of Ca(2+) channels. However, when nerve terminals are stimulated with low KCl concentrations (5-10 mmol/L) glutamate release is affected by both Ca(2+) antagonists and also by TTX and TEA, indicating the participation of Na(+) and K(+) channel firing in addition to Ca(2+) channel activation. Interestingly, stimulation of nerve terminals with low KCl concentrations uncovered a mechanism that further inhibited glutamate release (81.78 +/- 4.9%) and that was fully reversed by TEA. This additional mechanism is TTX-sensitive and consistent with the activation of K(+) channels. Furthermore, Ca(2+) imaging of single boutons demonstrated that the two pre-synaptic mechanisms by which cannabinoid receptors reduce glutamate release operate in distinct populations of nerve terminals.
authors.affiliation: Departamento de Bioquímica, Facultad de Veterinaria, Universidad Complutense, Madrid, Spain.
authors.forename: María del Carmen
authors.initials: Mdel C
authors.lastname: Godino
authors.forename: Magdalena
authors.initials: M
authors.lastname: Torres
authors.forename: José
authors.initials: J
authors.lastname: Sánchez-Prieto
mesh_terms: D000818:Animals; D048588:Benzoxazines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D002540:Cerebral Cortex / Q000502:physiology*; D018698:Glutamic Acid / Q000378:metabolism*; D008297:Male; D009025:Morpholines / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D043884:Receptor, Cannabinoid, CB1 / Q000502:physiology*; D013574:Synaptosomes / Q000502:physiology; D019789:Tetraethylammonium / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D048588:Benzoxazines; D015220:Calcium Channels; D009025:Morpholines; D009281:Naphthalenes; D043884:Receptor, Cannabinoid, CB1; D018698:Glutamic Acid; D013779:Tetrodotoxin; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; D019789:Tetraethylammonium; D011189:Potassium Chloride; D002118:Calcium