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Pharmacological fractionation of tetrodotoxin‐sensitive sodium currents in rat dorsal root ganglion neurons by μ‐conotoxins
Author(s) -
Zhang MinMin,
Wilson Michael J,
Gajewiak Joanna,
Rivier Jean E,
Bulaj Grzegorz,
Olivera Baldomero M,
Yoshikami Doju
Publication year - 2013
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/bph.12119
Subject(s) - dorsal root ganglion , tetrodotoxin , sodium channel , conotoxin , gene isoform , depolarization , sodium , biophysics , chemistry , biology , neuroscience , microbiology and biotechnology , anatomy , biochemistry , dorsum , peptide , gene , organic chemistry
Background and Purpose Adult rat dorsal root ganglion ( DRG ) neurons normally express transcripts for five isoforms of the α‐subunit of voltage‐gated sodium channels: Na V 1.1, 1.6, 1.7, 1.8 and 1.9. Tetrodotoxin ( TTX ) readily blocks all but Na V 1.8 and 1.9, and pharmacological agents that discriminate among the TTX ‐sensitive Na V 1‐isoforms are scarce. Recently, we used the activity profile of a panel of μ‐conotoxins in blocking cloned rodent Na V 1‐isoforms expressed in X enopus laevis oocytes to conclude that action potentials of A ‐ and C ‐fibres in rat sciatic nerve were, respectively, mediated primarily by Na V 1.6 and Na V 1.7. Experimental Approach We used three μ‐conotoxins, μ‐ TIIIA , μ‐ PIIIA and μ‐ SmIIIA , applied individually and in combinations, to pharmacologically differentiate the TTX ‐sensitive I Na of voltage‐clamped neurons acutely dissociated from adult rat DRG . We examined only small and large neurons whose respective I Na were >50% and >80% TTX ‐sensitive. Key Results In both small and large neurons, the ability of the toxins to block TTX ‐sensitive I Na was μ‐ TIIIA < μ‐ PIIIA < μ‐ SmIIIA , with the latter blocking ≳90%. Comparison of the toxin‐susceptibility profiles of the neuronal I Na with recently acquired profiles of rat Na V 1‐isoforms, co‐expressed with various Na V β‐subunits in X . laevis oocytes, were consistent: Na V 1.1, 1.6 and 1.7 could account for all of the TTX ‐sensitive I Na , with Na V 1.1 < Na V 1.6 < Na V 1.7 for small neurons and Na V 1.7 < Na V 1.1 < Na V 1.6 for large neurons. Conclusions and Implications Combinations of μ‐conotoxins can be used to determine the probable Na V 1‐isoforms underlying the I Na in DRG neurons. Preliminary experiments with sympathetic neurons suggest that this approach is extendable to other neurons.