Investigation of hyperpolarization-activated cyclic nucleotide-gated channels in interstitial cells of Cajal of human bladder.

OBJECTIVE: To investigate the expression of hyperpolarization-activated cyclic nucleotide-gated (HCN) protein in the interstitial cells of Cajal (ICCs) of the human bladder and to determine the relative expression of the HCN subtypes.
METHODS: A total of 30 bladder specimens were obtained, and each bladder sample was divided into 2 parts. Part I, which included mucosa, submucosa, and muscle, was used for immunofluorescence study. Part II, in which the mucosa and submucosa were removed and fresh bladder muscle tissue was kept, was used for Western blotting. First, the immunoreactivity of HCN1, HCN2, HCN3, and HCN4 isoforms was detected in the ICCs of lamina propria using immunofluorescence. Second, the protein expression of HCN1, HCN2, HCN3, and HCN4 isoforms in ICCs of bladder detrusor muscle was analyzed using Western blotting.
RESULTS: Immunofluorescence showed that there were many vimentin- and HCN4-positive ICCs in the lamina propria region and detrusor. Also, only a few c-kit and HCN4-positive ICCs were detected in the lamina propria region and detrusor. Additionally, novel c-kit negative, but HCN4-positive mast cells were found in the lamina propria. Immunofluorescence and Western blotting revealed that HCN1, HCN2, HCN3, and HCN4 channels were all present in the ICCs of the human bladder; however, HCN4 channel expression in the ICCs was greater than in HCN1, HCN2, or HCN3.
CONCLUSION: HCN1, HCN2, HCN3, and HCN4 channels are identified in ICCs of human bladder tissue, and the expression of the HCN4 channel exceeded that of the other subtypes.