Large conductance calcium-activated potassium channels (BKCa) modulate trigeminovascular nociceptive transmission

Migraine is a common, disabling, neurological problem whose acute management would benefit from the development of purely neurally acting therapies. The trigeminocervical complex is pivotal in nociceptive signaling in migraine, and is an accepted target for putative antimigraine agents. Whole-cell patch-clamp or extracellular recordings were made of trigeminal neurons identified in rat brainstem slices. Bath application of the large conductance calcium-activated potassium (BKCa) channel opener NS1619 caused a dramatic decrease of cell firing that could be reversed by the co-application of iberiotoxin. NS1619 hyperpolarized the resting membrane potential and reduced the frequency of spontaneous action potentials in these neurons. These data suggest the presence of BKCa channels in the trigeminocervical complex. In vivo in cat L-glutamate-evoked firing was facilitated in nociceptive neurons, also responding to stimulation of the superior sagittal sinus, in the trigeminal nucleus caudalis by the BKCa peptide antagonists, iberiotoxin and slotoxin. Of units tested, 70% responded to microiontophoretic application of the blockers, identifying a subpopulation of trigeminal neurons expressing toxin-sensitive BKCa channels. NS1619 inhibited 74% of cells tested, and this was reversed by slotoxin, suggesting that the action of NS1619 in these cells was mediated through BKCa channels. These data are consistent with the presence of BKCa channels in the trigeminal nucleus caudalis that are potential targets for the development of antimigraine treatments, and may also offer insights into receptor mechanisms involved in sensitization and thus allodynia, in migraine.