The modulation of voltage-dependent calcium currents (ICa) by serotonin (5-HT) was studied in rat acutely dissociated amygdala neurons using whole-cell patch-clamp recording techniques. 5-HT inhibited ICa in a concentration-dependent manner with a ED50 of ∼1 μM and a maximal inhibition of ∼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 μM) reduced the ICa by ∼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 ω-conotoxin-GVIA (ω-CgTX, 1 μM) or ω-agatoxin-IV (ω-AgTX, 200 nM), which blocked 26% and 21% of the total ICa, respectively, was significantly decreased, suggesting involvement of the N- and P/Q-type channels. In the combined presence of ω-CgTX and ω-AgTX, 5-HT still caused a small but significant reduction of ICa, suggesting a possible involvement of R-type channels. Stimulation of β-adrenergic receptor with isoproterenol (Iso) or activation of adenylyl cyclase with forskolin resulted in an enhancement of ICa. 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 ICa 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 ICa.
All Science Journal Classification (ASJC) codes
- Cellular and Molecular Neuroscience