Objective To investigate whether there is expression of hyperpolarization-activated cyclic nucleotide-gated cation channel (HCN) in normal bladder interstitial cells of Cajal (ICCs) and in ICCs of unstable bladder

so as to assess the relationship between the changes of ICCs excitability and the detrusor instability. Method ① Thirty SD rats were randomized into 3 groups:　normal(n=10)

detrusor stability(n=12) and detrusor instability (n=8

8 weeks after bladder outlet obstruction). ② The HCN protein expression in ICCs was detected with double-labeled immunofluorescence. The relationship of HCN protein and ICCs was accessed by double-labeled immunofluorescence with HCN and c-kit. ③ HCN expression of the 3 groups was also detected with Western blotting assay. Results ① HCN expression was well accorded to c-kit expression by using double-labeled immunofluorescence. ② With double-labeled immunofluorescence and Western blotting

HCN expression of DI and stable group was increased compared to the normal group

with statistical significance between the DI and normal groups (P0.01). Conclusion HCN protein is identified in ICCs of rat bladder. The expression of HCN protein is enhanced obviously in DI group

which may be responsible for the increased excitability of DI bladder.