Objective      To determine the effects of the knockout of hyper-polarization-activated

cyclic nucleotide-gated cation channels (HCN1 channels) on the expression and function of large-conductance calcium-activated potassium channels (BK channels) in interstitial cells of Cajal (ICCs) in the mouse bladder

and investigate the significance of these effects to the excitatory regulation of bladder.        Methods      Forty-eight healthy clean adult wild-type C57BL/6J mice (HCN1 WT) and 48 HCN1 channels knockout C57BL/6J mice (HCN1 KO) were employed in this study. The expression of BK channels and subunits in ICCs at mRNA and protein levels was detected by RT-PCR

Q-PCR

Western blotting and immunofluorescence staining.  The inhibitor of BK channel

IBTX

was added in the isolated detrusor muscle strips to observe the effect on muscle contraction. While

intracellular calcium concentration in ICCs were measured with laser confocal microscopy after the treatment of IBTX and the agonist of BK channels

NS1619

respectively.        Results      Q-PCR and Western blot results indicated that the expression of 5 BK channels’  subunits

α

β1

β2

β3 and β4 were significantly lower at mRNA level (P0.01) and at protein level (α

β3

β4: P0.01; β1

β2: P0.05) in the bladder of HCN1 KO mice than HCN1 WT mice. Double-labeling immunofluorescence staining revealed that the expression of α subunit was also lower in ICCs of HCN1 KO mice than HCN1 WT mice(P0.05). IBTX increased the amplitudes of detrusor contraction in the detrusor strip of HCN1 KO and WT mice (P0.01

P0.05)

but the KO mice detrusor had a lower sensitivity to IBTX (P0.05). NS1619 decreased while IBTX increased the intracellular calcium concentration of ICCs in both WT and KO mice (P0.05

P0.01)

but the actions of NS1619 and IBTX on KO mice were lower than WT mice (P0.01).        Conclusion      Knockout of HCN1 channels decreases the expression and function of BK channels in ICCs

and it might be a compensational mechanism of the decreased contractility induced by the knockout of HCN1 channels.