L-type channel inhibition by CB1 cannabinoid receptors is mediated by PTX-sensitive G proteins and cAMP/PKA in GT1-7 hypothalamic neurons.
Using immortalized hypothalamic GT1-7 neurons, which express the CB1 cannabinoid receptor (CB1R) and three Ca2+ channel types (T, R and L), we found that the CB1R agonist WIN 55,212-2 inhibited the voltage-gated Ca2+ currents by about 35%. The inhibition by WIN 55,212-2 (10 microM) was reversible and prevented by nifedipine (3 microM), suggesting a selective action on L-type Ca2+ channels (LTCCs). WIN 55,212-2 action exhibited all the features of voltage-independent Ca2+ channel modulation: (1) no changes of the activation kinetics, (2) equal depressive action at all potentials and (3) no facilitation following strong prepulses. At variance with WIN 55,212-2, the CB1R inverse agonist AM-251 (10 microM) caused 20% increase of Ca2+ currents. The inhibition of LTCCs by WIN 55,212-2 was prevented by overnight PTX-incubation and by intracellular perfusion with GDP-beta-S. The latter caused also a 20% Ca2+ current up-regulation. WIN 55,212-2 action was also prevented by application of the PKA-blocker H89 or by loading the neurons with 8-CPT-cAMP. Our results suggest that LTCCs in GT1-7 neurons are partially inhibited at rest due to a constitutive CB1R activity removed by AM-251 and GDP-beta-S. Activation of CB1R via PTX-sensitive G proteins and cAMP/PKA pathway selectively depresses LTCCs that critically control the synchronized spontaneous firing and pulsatile release of gonadotropin-releasing hormone in GT1-7 neurons.
Hoddah
Hanaa
H
Department of Biology, University Abdelmalek Essaadi, Tetouan, Morocco.
Marcantoni
Andrea
A
Comunanza
Valentina
V
Carabelli
Valentina
V
Carbone
Emilio
E
D000818:Animals; D048588:Benzoxazines / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D002460:Cell Line; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015536:Down-Regulation; D004594:Electrophysiology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D007031:Hypothalamus / Q000378:metabolism*; D007546:Isoquinolines / Q000494:pharmacology; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D055099:Neuroendocrine Cells / Q000378:metabolism*; D010880:Piperidines / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D043884:Receptor, Cannabinoid, CB1 / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013449:Sulfonamides / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology
D048588:Benzoxazines; D020746:Calcium Channels, L-Type; D007546:Isoquinolines; D009025:Morpholines; D009281:Naphthalenes; D010880:Piperidines; D011720:Pyrazoles; D043884:Receptor, Cannabinoid, CB1; D013449:Sulfonamides; D013873:Thionucleotides; D006153:Guanosine Diphosphate; C103505:AM 251; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; C023427:guanosine 5'-O-(2-thiodiphosphate); D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D019204:GTP-Binding Proteins; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide