Modulation of voltage-dependent calcium currents by serotonin in acutely isolated rat amygdala neurons.
The modulation of voltage-dependent calcium currents (I(Ca)) by serotonin (5-HT) was studied in rat acutely dissociated amygdala neurons using whole-cell patch-clamp recording techniques. 5-HT inhibited I(Ca) in a concentration-dependent manner with a ED50 of approximately 1 microM and a maximal inhibition of approximately 50%. The inhibition was mimicked by the selective 5-HT1A agonist 8-hydroxy-dipropylaminotetralin (8-OH-DPAT) and was reduced by the 5-HT1A antagonist NAN-190, indicating its mediation by 5-HT1A receptors. Pretreatment of neurons with the alkylating agent N-ethylmaleimide (NEM) or pertussis toxin (PTX) markedly reduced the action of 5-HT. The modulation was partially reversed by strong depolarization and was not seen in cell-attached patches when the agonist was applied outside the recorded patch, suggesting a membrane-delimited, G-protein-mediated signaling pathway. Nimodipine (1 microM) reduced the I(Ca) by approximately 30% without reducing inhibition of current by 5-HT significantly, ruling out L-type channels as the target of modulation. 5-HT-mediated inhibition after exposure to omega-conotoxin-GVIA (omega-CgTX, 1 microM) or omega-agatoxin-IV (omega-AgTX, 200 nM), which blocked 26% and 21% of the total I(Ca), respectively, was significantly decreased, suggesting involvement of the N- and P/Q-type channels. In the combined presence of omega-CgTX and omega-AgTX, 5-HT still caused a small but significant reduction of I(Ca), suggesting a possible involvement of R-type channels. Stimulation of beta-adrenergic receptor with isoproterenol (Iso) or activation of adenylyl cyclase with forskolin resulted in an enhancement of I(Ca). 5-HT caused the same degree of inhibition with or without Iso or forskolin pretreatment. On the other hand, application of 8-OH-DPAT inhibited I(Ca) and blocked Iso- and Sp-cAMPS-induced enhancement. These results provide the first evidence showing a dominant effect of 5-HT-mediated inhibition over Iso-mediated enhancement of I(Ca).
Lin
C H
CH
Department of Pharmacology, College of Medicine, National Cheng-Kung University, Tainan City, Taiwan 701.
Huang
Y C
YC
Tsai
J J
JJ
Gean
P W
PW
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000494:pharmacology; D037361:Adenylate Cyclase Toxin; D000262:Adenylyl Cyclases / Q000378:metabolism; D000679:Amygdala / Q000166:cytology* / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009553:Nimodipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D037342:Pertussis Toxin; D010879:Piperazines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013566:Sympathomimetics / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D020867:omega-Agatoxin IVA / Q000494:pharmacology; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004791:Enzyme Inhibitors; D010879:Piperazines; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D013566:Sympathomimetics; D013873:Thionucleotides; D010566:Virulence Factors, Bordetella; D020867:omega-Agatoxin IVA; C058895:1-(2-methoxyphenyl)-4-(4-(2-phthalimido)butyl)piperazine; D005576:Colforsin; C016957:adenosine-3',5'-cyclic phosphorothioate; D012701:Serotonin; D009553:Nimodipine; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D020866:omega-Conotoxin GVIA; D000242:Cyclic AMP; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D007545:Isoproterenol; D005033:Ethylmaleimide; D002118:Calcium