Decreased hyperpolarization-activated cyclic nucleotide-gated channels are involved in bladder dysfunction associated with spinal cord injury

Abstract

Spinal cord injury (SCI) leads to bereft voluntary control of bladder, but the possible role of spontaneous excited system in bladder of SCI patients is poorly understood. Hyper polarization-activated cyclic nucleotide-gated (HCN) channels are deemed to regulate the spontaneous contraction of bladder, our study explored the functional role of HCN channels in SCI induced neurogenic bladder. Sixty female Sprague-Dawley rats were randomized into control, sham and SCI groups. Rat models subjected to SCI at S2 levels were successfully established and were assessed using hematoxylin and eosin staining and cystometry. In SCI rats, the mRNA and protein expression levels of HCN channels and the I _h density were significantly reduced, and expression levels of several bladder HCN1 channel regulatory proteins were also significantly changed. The effects of 50 µM forskolin and 50 µM 8-bromoadenosine 3′,5′-cyclic monophosphate on [Ca ²⁺] _i of isolated bladder interstitial cells of Cajal-like cells were significantly decreased in SCI rats. The spontaneous contractions in detrusor strips from SCI rats were significantly weakened. Furthermore, detrusor strips from SCI rats exhibited decreased tolerance to two doses of ZD7288 (10 and 50 µM). Taken together, our results indicate that the decreased bladder HCN channel expression and function induced by altered regulatory proteins are involved in the pathological process of SCI induced neurogenic bladder, which present HCN channels as valid therapeutic targets for treating this disease.