Expression and distribution of the transient receptor potential cationic channel A1 (TRPA1) in the human clitoris-comparison to male penile erectile tissue.

The transient receptor potential cationic channel ankyrin 1 (TRPA1) is a channel protein assumed to act in various human tissues as mechano- and pain sensor and play a role in neurotransmission. The expression of TRPA has already been investigated in the human prostate and urethra, however, only very few studies have addressed the expression and distribution in the male and female genital tract. The present study aimed to investigate by means of immunohistochemistry (double-labeling technique, laser fluorescence microscopy) in the human clitoris and penile erectile tissue the localization of TRPA1 in relation to nNOS, the vasoactive intestinal polypeptide (VIP) and vesicular acetylcholine transporter (VAChT). In the clitoral tissue, TRPA1 was observed in basal epithelial cells and slender nNOS-positive nerve fibers transversing the subepithelial space. To a certain degree, in the clitoral epithelial cells, TRPA1 was found co-localized with vimentin. In human corpus cavernosum, immunoreactivity for TRPA1 was seen in nerves transversing the cavernous sinusoidal space and running alongside small arteries, these nerves also displayed expression of the vesicular acetylcholine transporter protein (VAChT). Varicose nerves containing nNOS or VIP were not immunoreactive for TRPA1. It seems likely that TRPA1 is involved in nitric oxide-mediated afferent sensory transmission in the clitoris while, in penile erectile tissue, a role for TRPA1 in cholinergic signaling might be assumed.