ω-Phonetoxins inhibit voltage-gated calcium Ca V 2.2 ion channel splice isoforms of dorsal root ganglia.

Cell-specific alternative splicing of Cacna1b pre-mRNA generates functionally distinct voltage-gated Ca V 2.2 channels. Ca V 2.2 channels mediate the release of glutamate from nociceptor termini in the dorsal horn spinal cord and they are implicated in chronic pain. One alternatively spliced exon in Cacna1b , e37a, is highly expressed in dorsal root ganglia, relative to other regions of the nervous system, and it is particularly important in inflammatory hyperalgesia. Here we studied the effects of two ω-phonetoxins, PnTx3-4 and Phα1β, derived from the spider Phoneutria nigriventer on Ca V 2.2 channel isoforms of dorsal root ganglia (Ca V 2.2 e37a and Ca V 2.2 e37b). Both PnTx3-4 and Phα1β are known to have analgesic effects in rodent models of pain and to inhibit Ca V 2.2 channels. Ca V 2.2 e37a and Ca V 2.2 e37b isoforms expressed in a mammalian cell line were inhibited by PnTx3-4 and Phα1β with similar potency and with similar timecourse, although Ca V 2.2 e37a currents were slightly, but consistently more sensitive to toxin inhibition compared to Ca V 2.2 e37b. The inhibitory effects of PnTx3-4 and Phα1β on Ca V 2.2-e37a and Ca V 2.2-e37b channels were voltage-dependent, and both occlude the inhibitory effects of ω-conotoxin GVIA, consistent with a common site of action. The potency of PnTx3-4 and Phα1β on both major splice isoforms in dorsal root ganglia constribute to understanding the analgesic actions of these ω-phonetoxins.