Acid-induced CGRP release from the stomach does not depend on TRPV1 or ASIC3.
BACKGROUND
Acid-sensing and regulating reactions are vitally important in the upper gastrointestinal tract and disturbances are common. Sensory neurons in the mucosa detect the intrusion of hydrogen ions and, by their release of vasoactive neuropeptides, seem to play a predominantly protective role in these tissues.


METHODS
The model to investigate sensory transduction of proton stimuli in the isolated everted mouse stomach was to measure the induced calcitonin gene-related peptide (CGRP) release as an index of neuronal activation.


RESULTS
Proton concentrations in the range of pH 2.5-0.5 stimulated the release of CGRP and substance P and profoundly decreased the prostaglandin E2 formation in outbred CD mice. A similar linearly pH-dependent CGRP release was observed in inbred C57BL/6 mice, fully dependent on extracellular calcium at pH 2, partially at pH 1. Both transient receptor potential vanilloid type 1 (TRPV1) and acid-sensing ion channel type 3 (ASIC3) are expressed in the sensory neurons innervating the stomach walls and are responsible for the transduction of acidic stimuli in other visceral organs. However, the proton-induced gastric CGRP release in mice lacking the TRPV1 or the ASIC3 receptor-channels was the same as in corresponding wild-type mice. Nonetheless, the pharmacological blockers N-(4-tertiarybutylphenyl)-4-(3-chlorophyridin-2-yl)tetrahydropyrazine-1(2H)carboxamide and amiloride, respectively, inhibited the acid-stimulated CGRP release, although to the same extend in wild types as TRPV1 and ASIC3 knockout mice.


CONCLUSIONS
Adequate proton concentrations inhibit prostaglandin and stimulate CGRP release from the stomach wall, however, the transduction mechanism in the gastric sensory neurons remains unclear.
Auer
J
J
Institute of Physiology and Pathophysiology, University of Erlangen-Nürnberg, Erlangen, Germany.
Reeh
P W
PW
Fischer
M J M
MJ
D062565:Acid Sensing Ion Channels; D000143:Acids; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism*; D003627:Data Interpretation, Statistical; D015232:Dinoprostone / Q000378:metabolism; D005753:Gastric Mucosa / Q000187:drug effects / Q000294:innervation / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007124:Immunoenzyme Techniques; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D015222:Sodium Channels / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D013270:Stomach / Q000187:drug effects; D013373:Substance P / Q000378:metabolism; D050916:TRPV Cation Channels / Q000187:drug effects / Q000235:genetics / Q000502:physiology*
C508378:ASIC3 protein, mouse; D062565:Acid Sensing Ion Channels; D000143:Acids; D015222:Sodium Channels; D050916:TRPV Cation Channels; C493921:TRPV1 protein, mouse; D013373:Substance P; D000584:Amiloride; D015740:Calcitonin Gene-Related Peptide; D015232:Dinoprostone