3.1.4. DAG lipase is required for bradykinin-induced enhancing
of capsaicin cells
The results above have shown that bradykinin-induced sensitisation of
capsaicin-sensitive neurons is mediated by EP4 and cyclooxygenase. To
investigate this further we looked at the DAG lipase branch of the PLC
pathway since PLC activation results in the production of DAG which can
then metabolised to arachidonic acid by cyclooxygenase enzymes,
particularly the constitutively expressed isoform, COX-1. To confirm
this, experiments were conducted to examine the effect of DAG lipase
inhibitor, RHC-80267, on the bradykinin-induced enhancement of
capsaicin-induced calcium responses in cultured DRG neurons.
Figure 5A representative traces showing the effect of the DAG lipase
inhibitor RHC-80267 on capsaicin responses and its effect on bradykinin
mediated sensitisation following bradykinin application. Capsaicin
(80nm; 10seconds) was applied twice in absence and presence of BK
(100nM; 3-minutes, bar) with second application in presence of BK and
the DAG lipase inhibitor, RHC-80267 (20µM; 20minutes).
RHC-80267 (20µM; 20 min) attenuated the bradykinin-induced sensitisation
of capsaicin-induced calcium responses (Fig 5B). The response ratio of
the first and second capsaicin responses was 61.9± 4.9 % in the
presence of (RHC-80267 +bradykinin) which was significantly reduced
compared to the effect of bradykinin alone (115±11.8 %).(** P< 0.01, one-way ANOVA by Bonferroni’s multiple comparison
tests).