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.