Figure 6.

Pharmacological experiments suggest that at least two types of sensory nerves expressing TRP channels innervate guinea pig urinary bladder. TRPA1 channels are located on one population of nerves (Type A). Activation of TRPA1 in these nerves and/or unidentified non-neuronal cells by AITC excites bladder smooth muscle; an effect blocked by indomethacin indicating that the excitation is mediated by the synthesis and release of prostaglandins (PGs). Another population of sensory nerves (Type B) expresses TRPV1, TRPA1, and TRPC channels. Activation of these channels by capsaicin (CAPS), AITC, or OA-NO₂ releases CGRP causing inhibition of the bladder smooth muscle. However, in comparison to the prominent effects of CAPS and OA-NO₂ the inhibitory effect of AITC mediated by CGRP release from Type B nerves is relatively weak and only detectable when prostaglandin (PG) synthesis is blocked by indomethacin indicating that it is normally masked by the PG excitation. (+): excitatory; (–): inhibitory.