Bimodal concentration-response of nicotine involves the nicotinic acetylcholine receptor, transient receptor potential vanilloid type 1, and transient receptor potential ankyrin 1 channels in mouse trachea and sensory neurons.
High concentrations of nicotine, as in the saliva of oral tobacco consumers or in smoking cessation aids, have been shown to sensitize/activate recombinant transient receptor potential vanilloid type 1 (rTRPV1) and mouse TRPA1 (mTRPA1) channels. By measuring stimulated calcitonin gene-related peptide (CGRP) release from the isolated mouse trachea, we established a bimodal concentration-response relationship with a threshold below 10 µM (-)-nicotine, a maximum at 100 µM, an apparent nadir between 0.5 and 10 mM, and a renewed increase at 20 mM. The first peak was unchanged in TRPV1/A1 double-null mutants as compared with wild-types and was abolished by specific nicotinic acetylcholine receptor (nAChR) inhibitors and by camphor, discovered to act as nicotinic antagonist. The nicotine response at 20 mM was strongly pHe-dependent, - five times greater at pH 9.0 than 7.4, indicating that intracellular permeation of the (uncharged) alkaloid was required to reach the TRPV1/A1 binding sites. The response was strongly reduced in both null mutants, and more so in double-null mutants. Upon measuring calcium transients in nodose/jugular and dorsal root ganglion neurons in response to 100 µM nicotine, 48% of the vagal (but only 14% of the somatic) sensory neurons were activated, the latter very weakly. However, nicotine 20 mM at pH 9.0 repeatedly activated almost every single cultured neuron, partly by releasing intracellular calcium and independent of TRPV1/A1 and nAChRs. In conclusion, in mouse tracheal sensory nerves nAChRs are 200-fold more sensitive to nicotine than TRPV1/A1; they are widely coexpressed with the capsaicin receptor among vagal sensory neurons and twice as abundant as TRPA1. Nicotine is the major stimulant in tobacco, and its sensory impact through nAChRs should not be disregarded.
Institute of Physiology and Pathophysiology (T.I.K., J.L., M.E., R.M.B., P.W.R.) and Institute of Anatomy I (W.N.), Friedrich-Alexander-University, Erlangen, Germany; Institute of Pathology, University of Ulm, Ulm, Germany (J.L.); Department of Biophysics, Carol Davila University of Medicine and Pharmacy, Bucharest, Romania (R.M.B.); Department of Anesthesiology and Intensive Care, Hannover Medical School, Hannover, Germany (M.E.); and Altria Client Services, Inc., Richmond, Virginia (G.K.).
Tatjana I
TI
Kichko
Jochen
J
Lennerz
Mirjam
M
Eberhardt
Ramona M
RM
Babes
Winfried
W
Neuhuber
Gerd
G
Kobal
Peter W
PW
Reeh
D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism; D018929:Cell Culture Techniques; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005260:Female; D017950:Ganglia, Sensory / Q000187:drug effects* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009538:Nicotine / Q000008:administration & dosage / Q000494:pharmacology*; D011978:Receptors, Nicotinic / Q000235:genetics / Q000378:metabolism*; D011984:Sensory Receptor Cells / Q000187:drug effects* / Q000378:metabolism; D000074025:TRPA1 Cation Channel; D050916:TRPV Cation Channels / Q000235:genetics / Q000378:metabolism*; D014132:Trachea / Q000187:drug effects* / Q000378:metabolism; D050051:Transient Receptor Potential Channels / Q000235:genetics / Q000378:metabolism*
D011978:Receptors, Nicotinic; D000074025:TRPA1 Cation Channel; D050916:TRPV Cation Channels; C493921:TRPV1 protein, mouse; D050051:Transient Receptor Potential Channels; C475685:Trpa1 protein, mouse; D009538:Nicotine; D015740:Calcitonin Gene-Related Peptide