Localization of large conductance calcium-activated potassium channels and their effect on calcitonin gene-related peptide release in the rat trigemino–neuronal pathway

Abstract

Large conductance calcium-activated potassium (BKCa) channels are membrane proteins contributing to electrical propagation through neurons. Calcitonin gene-related peptide (CGRP) is a neuropeptide found in the trigeminovascular system (TGVS). Both BKCa channels and CGRP are involved in migraine pathophysiology. Here we study the expression and localization of BKCa channels and CGRP in the rat trigeminal ganglion (TG) and the trigeminal nucleus caudalis (TNC) as these structures are involved in migraine pain. Also the effect of the BKCa channel blocker iberiotoxin and the BKCa channel opener NS11021 on CGRP release from isolated TG and TNC was investigated. By RT-PCR, BKCa channel mRNA was detected in the TG and the TNC. A significant difference in BKCa channel mRNA transcript levels were found using qPCR between the TNC as compared to the TG. The BKCa channel protein was more expressed in the TNC as compared to the TG shown by western blotting. Immunohistochemistry identified BKCa channels in the nerve cell bodies of the TG and the TNC. The β2- and β4-subunit proteins were found in the TG and the TNC. They were both more expressed in the TNC as compared to TG shown by western blotting. In isolated TNC, the BKCa channel blocker iberiotoxin induced a concentration-dependent release of CGRP that was attenuated by the BKCa channel opener NS11021. No effect on basal CGRP release was found by NS11021 in isolated TG or TNC or by iberiotoxin in TG. In conclusion, we found both BKCa channel mRNA and protein expression in the TG and the TNC. The BKCa channel protein and the modulatory β2- and β4-subunt proteins were more expressed in the TNC than in the TG. Iberiotoxin induced an increase in CGRP release from the TNC that was attenuated by NS11021. Thus, BKCa channels might have a role in trigeminovascular pain transmission.