P2X2 and P2X3 receptor expression in the gallbladder of the guinea pig

We investigated for the first time, the distribution pattern of P2X2 and P2X3 receptors in the gallbladder of the guinea pig using immunohistochemistry. P2X2 and P2X3 receptor-immunoreactive nerve fibers were observed within the ganglia, in the interganglionic connectives, in the muscularis and in the paravascular plexus. Immunoreactivity for P2X2 and P2X3 was also observed in most neurons in the ganglionated plexus. Double-labeling studies revealed that 58.1% of all P2X2-positive neurons and 54.3% of all P2X3-positive neurons were found to display nitric oxide synthase. Over 90% of the neurons that were immunoreactive for P2X2 and P2X3 receptor were also immunoreactive for calretinin. We also found that 30.5% of P2X2- and 32.6% of P2X3-immunoreactive neurons were also immunoreactive for vasoactive intestinal peptide. No P2X2- or P2X3- immunoreactive neurons stained for calcitonin gene-related peptide; a few calcitonin gene-related peptide-immunoreactive nerve fibers also showed immunoreactivity to P2X2 or P2X3 receptors. These results further demonstrate the neurotransmitter diversity of the nerves of the gallbladder and provide an incentive for studies of the actions of these compounds in the gallbladder wall.