Changes in hyperpolarization-activated cyclic nucleotide-gated channel expression and activity in bladder interstitial cells of Cajal from rats with detrusor overactivity

Introduction and hypothesis To investigate changes in the expression and function of the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, interstitial cells of Cajal (ICCs) were isolated from detrusor overactivity (DO) rats induced with partial bladder outlet obstruction (PBOO). We hypothesized that increased expression of HCN channels in ICCs would enhance the excitability of ICCs and bladder in DO rats. Methods Forty adult female Sprague-Dawley rats were randomly assigned to control and DO groups. The expression of HCN isoforms in the rat bladders was detected using reverse transcription-polymerase chain reaction (RT-PCR). Whole-cell patch-clamp techniques and laser confocal microscopy were used to explore the effects of the HCN channel blocker ZD7288 on Ih current and intracellular calcium levels ([Ca2+](i)) in freshly isolated ICCs. The effect of ZD7288 on bladder contraction was evaluated using a bladder smooth muscle strip test. Results The results of RT-PCR showed that HCN1-4 isoforms increased expression in the DO group compared with the control group. The current density of Ih in the bladder ICCs was increased. A moderate concentration of ZD7288 (50 mu mol/L) significantly decreased the [Ca2+](i) levels in freshly isolated ICCs from sham and DO bladders. The smooth strip tests indicated that ZD7288 (50 mu mol/L) suppressed the amplitude of smooth muscle strip contractions in the sham and DO bladders. Conclusions All HCN channel isoforms were highly expressed in bladders from the DO group, which was correlated with increased Ih currents in DO ICCs, suggesting that the HCN channels might play an important role in the pathological processes of DO.