Heat-induced release of CGRP from isolated rat skin and effects of bradykinin and the protein kinase C activator PMA

In the skin, noxious heating induces an axon reflex response which is commo nly accepted to be due to the release of vasodilatory neuropeptides from po lymodal nociceptors. In the present study, the quantitative assessment of c alcitonin gene-related peptide (CGRP) release from rat skin serves as an in tegrative measure of primary afferent activation by noxious heat and the pr esumed sensitising action of bradykinin and an activator of protein kinase C (PKC). The isolated rat hairy skin of either hind paw was mounted on acry lic rods and exposed for 5 min periods to synthetic interstitial fluid of e ither 32 degrees C for control or of higher temperatures up to 59 degrees C during stimulation. In addition, experiments were performed in calcium fre e solution (containing 10 mM EGTA) or the skin was preloaded with the membr ane permeant calcium chelator BAPTA-AM (1 mM). To look for modulatory effec ts on the heat responses, bradykinin or polymyristate-acetate (PMA) were ad ded during heat stimulation in further experiments. Heating the skin induce d a temperature-dependent release of CGRP from a threshold of 43 degrees C which was absent in calcium free solution. Only at the highest temperatures (55 and 59 degrees C) was a partially calcium-independent release observed . Inhibition of the release was also obtained with the intracellular calciu m buffer BAPTA-AM. Bradykinin 10 but not 1 mu M as well as PMA 1 and 10 mu M significantly facilitated the heat-induced CGRP release at 47 degrees C w hereby BK caused a marginal and PMA a significant CGRP release by itself. O ur results indicate that moderate noxious heat induces calcium-dependent CG RP release and this can be facilitated by bradykinin and by the activation of PKC. This suggests the same sensitising mechanism that affects nocicepto r heat responses. (C) 1999 International Association for the Study of Pain. Published by Elsevier Science B.V.