title: Changes in cytosolic calcium in response to noxious heat and their relationship to vanilloid receptors in rat dorsal root ganglion neurons.
abstract: Heat transduction mechanisms in primary nociceptive afferents have been suggested to involve a vanilloid receptor channel with high calcium permeability. To characterize the changes in free cytosolic calcium evoked by noxious heat stimuli (< or =51 degrees C, 10s), we performed microfluorometric measurements in acutely dissociated small dorsal root ganglion neurons (< or =32.5 microm) of adult rats using the dye FURA-2. Only neurons that responded with a reversible increase in intracellular calcium to high potassium were evaluated. Heat-induced calcium transients (exceeding mean + 3S.D. of the temperature dependence of the dye) were found in 66 of 105 neurons. These transients increased non-linearly with temperature. In contrast, heat-insensitive neurons showed a small linear increase of intracellular calcium throughout the range of 12-49 degrees C, similar to cardiac muscle cells. The vanilloid receptor agonist capsaicin induced calcium transients in 72 of 99 neurons. Capsaicin sensitivity and heat sensitivity were significantly associated (P<0.001, chi(2)-test), but 16 of 34 heat-insensitive cells responded to capsaicin and four of 49 heat-sensitive cells were capsaicin insensitive. The competitive vanilloid receptor antagonist capsazepine (10 microM) reversibly reduced the heat-induced calcium transients by 47+/-13%. In contrast, high potassium-induced calcium transients were not affected by pre-incubation with capsazepine. In calcium-free extracellular solution, the heat-induced rise in intracellular calcium was reduced by 76+/-5%. Heat-induced calcium transients were also reversibly reduced by 75+/-6% in sodium-free solution and by 62+/-7% with the L-type calcium channel blocker nifedipine (5 microM). These results indicate that noxious heat rapidly increases intracellular calcium in nociceptive primary sensory neurons. Heat-sensitive vanilloid receptors are involved in the induction of calcium transients, and calcium is also released from intracellular stores, but the main fraction of calcium passes through voltage-operated calcium channels.
authors.affiliation: Institute of Physiology and Pathophysiology, Johannes Gutenberg University, D-55099, Mainz, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Greffrath
authors.forename: T
authors.initials: T
authors.lastname: Kirschstein
authors.forename: H
authors.initials: H
authors.lastname: Nawrath
authors.forename: R
authors.initials: R
authors.lastname: Treede
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002211:Capsaicin / Q000494:pharmacology; D002478:Cells, Cultured / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D005456:Fluorescent Dyes / Q000493:pharmacokinetics; D016257:Fura-2 / Q000493:pharmacokinetics; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006358:Hot Temperature / Q000009:adverse effects; D008297:Male; D009206:Myocardium / Q000378:metabolism; D009475:Neurons, Afferent / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009619:Nociceptors / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010146:Pain / Q000378:metabolism* / Q000503:physiopathology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011955:Receptors, Drug / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013697:Thermosensing / Q000187:drug effects / Q000502:physiology
chemical_list: D015220:Calcium Channels; D005456:Fluorescent Dyes; D011955:Receptors, Drug; D011188:Potassium; D002211:Capsaicin; D002118:Calcium; D016257:Fura-2