Acidic pH and capsaicin activate mechanosensitive group IV muscle receptors in the rat.
Strenuous exercise of muscle as well as inflammation and ischaemia are associated with tissue acidosis. However, so far, nothing is known about the sensitivity to hydrogen ions of slowly conducting muscle afferent units. The study investigated if acid-sensing ion channels, e.g. the polymodal acid/capsaicin-sensitive vanilloid receptors, were present on unmyelinated (group IV) muscle afferent units of the gastrocnemius-soleus muscle of the rat. Intramuscular injections of acidic phosphate buffer pH 6 excited 56.0% of the group IV units. A similar proportion (54.29%) was activated by capsaicin (655 microM). Tests of the same unit with both adenosine triphosphate at neutral pH (ATP, 7.6 mM; pH 7.4) and acidic phosphate demonstrated that most acid-sensitive units were also excited by ATP at neutral pH. The data show that (1) a high proportion of group IV muscle receptors are responsive to an increased extracellular hydrogen ion concentration, and (2) a subpopulation of these units are sensitive to both acidic pH and ATP.
Institut für Pharmakologie und Toxikologie, Charité, Humboldt-Universität, Dorotheenstrasse 94, D-10117 Berlin, Germany.
Ulrich
U
Hoheisel
Jochen
J
Reinöhl
Thomas
T
Unger
Siegfried
S
Mense
D000200:Action Potentials / Q000187:drug effects; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D002452:Cell Count; D048429:Cell Size; D005727:Ganglia, Spinal / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007150:Immunohistochemistry / Q000379:methods; D007273:Injections, Intramuscular / Q000379:methods; D008297:Male; D008465:Mechanoreceptors / Q000187:drug effects* / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects; D036421:Nerve Fibers, Unmyelinated / Q000187:drug effects* / Q000502:physiology; D009431:Neural Conduction / Q000187:drug effects; D009475:Neurons, Afferent / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects; D011955:Receptors, Drug / Q000378:metabolism; D018048:Receptors, Purinergic P2 / Q000378:metabolism; D058477:Receptors, Purinergic P2X3
C546410:P2rx3 protein, rat; D011955:Receptors, Drug; D018048:Receptors, Purinergic P2; D058477:Receptors, Purinergic P2X3; D000255:Adenosine Triphosphate; D002211:Capsaicin