The Role Of ICC In Excitability Change Of Neurogenic Bladder

Background and objectiveThe aim of this study is to investigate the role of interstitial cell of Cajal(ICC) in excitability change of neurogenic bladder. Neurogenic bladder, which is always caused by spinal cord injury, is a common bladder dysfunction. According to the segment of lesion, spinal cord injury can be classified as sacral cord injury(SCI) and Suprasacral cord injury(SSCI). SCI induce detrusor areflexia(DA), which displays contraction dysfunction or atony in bladder during voiding phase. SSCI induce detrusor hyperreflexia (DH), which displays spontaneous or evoked contraction in bladder during filling phase. According to the traditional theory, the bladder without the control of primary micturition center may display no contraction during voiding phase when the injury locates at sacral cord primary micturition center. The bladder under the control of primary micturition center and without the control of high centeral may display hyperreflexia when the injury locates at upper sacral cord. However, these theories can not explain the further changes of detrusor after nerve injury, such as muscle cells arranging disorder and maldistribution, intercellular space widening or nonuniform with decrease of elastic fibers and increase of collagen fibers, or decrease of intermediate junction following with appearance of gap junction. Moreover, SCI and SSCI always have the similar pathological change, which indicates we have not get enough data on the pathophysiological changes inducing the changes of bladder function.ICCs act as the pacemaker of smooth muscle activation in gastrointestinal tract. They play a role in producing gastrointestinal basic electrical rhythm(BER), transmitting electrical signal and mediating the signal between intestinal nerve and smooth muscle. It's important for ICCs to maintain normal structure, distribution and function to regulate gastrointestinal motility. The abnormal distribution of ICCs and the destroy of cellular network may related with gastrointestinal motility disorders, such as Hirschsprung's disease and chronic transmitting constipation. Recently, several investigators found that there are ICCs in many organs, such as renal pelvis, ureter and bladder, using phase contrast microscope, immunohistochemical anlysis and electron microscopy. However, the role of ICCs in urinary tract is still unknown. Studies demonstrated that ICCs in urinary tract presented spontaneous excitability. Some further studies indicated that the number of ICCs in the pyeloureteral junction decreased in patients with congenital pyeloureteral junction obstruction, and the number of ICCs in bladder decreased in patients with megacystis-microcolon intestinal hypoperistalsis syndrome. The munber of ICCs increased in overactivity bladder with the bladder outlet obstruction. Previously we found that ICCs increased significantly in bladder with BOO in rats model, which indicated ICCs may contribute to bladder activity. Therefor, we speculate that ICCs may contribute to detrusor hyperreflexia or detrusor areflexia in neurogenic bladder.C-kit receptors, which determined by a proto-oncogene kit encoding tyrosine kinase receptors, specially express in ICCs. The signal mediated by kit is important to maintain the development and function of cells. Imatinib mesylate (Glivec) is a selective inhibitor of c-kit receptor tyrosine kinases, and has USA Food and Drug Administration approval for the treatment of Philadelphia chromosome-positive chronic myeloid leukaemia and c-kit positive gastrointestinal stromal tumours. The data demonstrate that Glivec block kit signaling expression in gastrointestinal tract, and can suppress the spontaneous activity in bladder and the spontaneous action potential in detrusor in guinea pigs, suggests that ICCs contribute to the spontaneous activity in bladder and the spontaneous action potential in detrusor.The present study purposes to investigate the role of ICCs in the changes of detrusor hyperreflexia and detrusor areflexia in the bladder. We detect the changes of quantity and excitability of the ICCs in rats with detrusor hyperreflexia and detrusor areflexia, respectively. And we observe the changes of excitability of ICCs, the spontaneous activity of strips and bladder function, using c-kit receptor inhibitor Glivec to block ICCs in vitro and in vivo.MethodsFemale SD rats were used in the present study. These rats were randomly divided into normal group, post-cystostomy group, SSCI group and SCI group. The following studies were performed: 1. The bladders of rats were harvested in 4-6 weeks after spinal cord injury or cystostomy. The number of ICCs in each group was counted by immunofluorescence staining. 2. The ICCs of bladder in each group were freshly dispersed and the spontaneous calcium waves of ICCs were detected using laser confocal microscopy. 3. The changes of the spontaneous calcium waves of ICCs, the spontaneous contraction of the bladder strips and the changes of bladder function were detected after Glivec blocked the ICCs in each group.Results1,We successfully create the rat model with detrusor hyperreflexia and detrusor arereflexia.2,There are significantly more ICCs in bladder of SSCI rats than that in normal and post-cystostomy rats bladder. The quantity of ICCs in normal bladder is similar to that in post-cystostomy bladder. There are significantly less ICCs in bladder of SCI rats than that in normal and post-cystostomy rats bladder.3,We successfully freshly disperse and identify ICCs in rats bladder.4,The spongtanous excitability of ICCs in SSCI rats is higher than that in normal and post-cystostomy rats. The spongtanous excitability of ICCs in normal rats is similar to that in post-cystostomy rats. The spongtanous excitability of ICCs in SCI rats is lower than that in normal and post-cystostomy rats.5,The spontaneous calcium waves of ICCs in bladder is suppressed by Glivec with dose dependent. Glivec in low concentration(1×10-6mol/L) suppress the spontaneous calcium waves of ICCs in bladder with detrusor hyperreflexia, while 5×10-5mol/L Glivec suppress the spontaneous calcium waves of ICCs in bladder with detrusor areflexia.6,Each group has different spontaneous contractions of bladder in rats with unvarying preload(1g). The amplitude of spontaneous contractions of bladder with detrusor hyperreflexia in rats is higher than that in bladder with detrusor areflexia.7,The amplitude of spontaneous contraction of detrusor strips is inhibited by Glivec application with dose dependent. Glivec in low concentration(1×10-5mol/L) suppress the amplitude of spontaneous contraction of detrusor strips with detrusor hyperreflexia in rats, while 5×10-4mol/L Glivec suppress the amplitude of spontaneous contraction of detrusor strips with detrusor areflexia.8,Glivec(10mg/kg) increase the bladder capacity and compliance in rats with detrusor hyperreflexia and can not influence the bladder capacity and compliance in rats with detrusor areflexia. The spontaneous contraction of bladder can be suppressed by Glivec(20mg/kg) during the storage phase.Conclusion1. ICCs in rat bladder with spinal cord injury, including SSCI and SCI,occur to the changes of quantity and excitability.2. Glivec can suppress the spontaneous contraction of detrusor strips, increase the bladder capacity and compliance, and inhibit the spontaneous contraction of bladder with detrusor hyperreflexia by blocking ICCs, whereas it can not suppress the spontaneous contraction of detrusor strips, increase the capacity and compliance of bladder with detrusor arereflexia by blocking ICC.3. The increase of ICCs quantity and excitability may contribute to the bladder function of detrusor hyperreflexia, and the decrease of ICCs quantity and excitability may involve in the bladder function of detrusor arereflexia.4. Glivec increase the bladder capacity and compliance, and inhibit the spontaneous contraction of bladder with detrusor hyperreflexia. These results indicate that Glivec may be a new strategy for the clinical treatment of detrusor hyperreflexia.