The function of hyperpolarization-activated cyclic nucleotide-gated channel in diabetic cystopathy

OBJECTIVE: We aimed at investigating changes in the expression and physiological function of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels in interstitial cells of Cajal (ICC) in diabetic state.

MATERIALS AND METHODS: Twenty adult female Sprague-Dawley (SD) rats were randomly assigned to control and Zucker diabetic fatty (ZDF) group. The protein and mRNA expression of HCN isoforms and C-kit in the rat bladders were detected using Western blotting and reverse transcription-polymerase chain reaction (RT-PCR). The bladder contraction was evaluated using a bladder smooth muscle strip test. Whole cell patch-clamp techniques were used to detect the activity of HCN channels. Immunofluorescent staining was used to the positive expression of HCN and C-kit in ICC.

RESULTS: cAMP, as HCN channel-specific stimulant, could increase the frequency and amplitude of spontaneous contractions in both group, while cAMP inducing contraction of ZDF rats, was still significantly lower compared with the control group. Acute bladder ICCs were isolated by collagenase digestion. Classic Ih current pattern was recorded on ICCs while Ih current amplitude of ICCs from ZDF diabetic rats was significantly lower than the control group. The expression and mRNA of HCN1-4 isoforms in ZDF diabetic rats were both significantly lower compared with the control group. Meanwhile, the number of c-kit positive cells in ZDF diabetic rats showed no significant differences compared with controls. The morphological structure of ICC in the bladder of ZDF rats was relatively loose and the number of their cell process was apparently decreased.

CONCLUSIONS: The structure of ICCs in ZDF rats was relatively loose, their connection to each other was also diminished. The expression of HCN was down-regulated and its response to cAMP was also decreased. HCN channels in bladder ICCs might regulate detrusor contraction. Changes in HCN expression and activity in bladder ICCs might be one of the most important mechanisms of diabetic cystopathy.

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