Objective  To investigate the distribution of hyperpolarization-activated cyclic nucleotide-gated channel 2-positive cells (HCN2)

in the myenteric nerve plexus of gastrointestinal tract of mice.   Methods  Gastrointestinal tract samples

which included the stomach

small intestine and colon

from mature Kunming mice were collected for the preparation of whole-mount preparations

and then examined by immunocytochemistry for HCN2

cholinergic nerves and interstitial cells of Cajal (ICCs) with fluorescence microscopy and laser confocal microscopy. The markers of cholinergic nerves (ChAT) and ICCs (c-kit) were used to doubleimmunostaining with HCN2 channel.   Results  Most of HCN2-positive cells within the myenteric plexus of mature mice were Dogiel Ⅱ type-neurons and positive products occurred on the cell membranes and cytoplasm. They often gathered in cluster in the ganglia

which contained several to dozens of IR cells for HCN2. IR products were seen on nervous process

but majority occurred on those which were thicker. The density of distribution for HCN2-positive cells in the gastrointestinal tract was different: that of the colon was highest (P0.05)

that of the stomach was lower than that of the colon (P0.05)

and that of the small intestine was lowest (P0.05). HCN2 channel were found in the cholinergic nerves

although HCN2 channel not found in the soma of ICCs. The processes of ICCs were close to the HCN2-positive cells.   Conclusion  HCN2 channels are widely distributed in the myenteric nerve plexus

and primary expressed in the cholinergic nerves. HCN2 channels maybe involved in its regulation of gastrointestinal neural electrical activity

release of neurotransmitter and regulation of gastrointestinal function.