Antimigraine drug, zolmitriptan, inhibits high-voltage activated calcium currents in a population of acutely dissociated rat trigeminal sensory neurons

Abstract

Background: Triptans, 5-HT IB/ID agonists, act on peripheral and/or central terminals of trigeminal ganglion neurons (TGNs) and inhibit the release of neurotransmitters to second-order neurons, which is considered as one of key mechanisms for pain relief by triptans as antimigraine drugs. Although high-voltage activated (HVA) Ca2+ channels contribute to the release of neurotransmitters from TGNs, electrical actions of triptans on the HVA Ca2+ channels are not yet documented. Results: In the present study, actions of zolmitriptan, one of triptans, were examined on the HVA Ca2+ channels in acutely dissociated rat TGNs, by using whole-cell patch recording of Ba2+ currents (IBa) passing through Ca2+ channels. Zolmitriptan (0.1-100 μM) reduced the size of IBa in a concentration-dependent manner. This zolmitriptan-induced inhibitory action was blocked by GR127935, a 5-HTIB/ID antagonist, and by overnight pretreatment with pertussis toxin (PTX). P/Q-type Ca2+ channel blockers inhibited the inhibitory action of zolmitriptan on IBa, compared to N-and L-type blockers, and R-type blocker did, compared to L-type blocker, respectively (p < 0.05). All of the present results indicated that zolmitriptan inhibited HVA P/ Q- and possibly R-type channels by activating the 5-HTIB/ID receptor linked to Gi/o pathway. Conclusion: It is concluded that this zolmitriptan inhibition of HVA Ca2+ channels may explain the reduction in the release of neurotransmitters including CGRP, possibly leading to antimigraine effects of zolmitriptan. © 2006 Morikawa et al; licensee BioMed Central Ltd.