| Background and Objective: Bladder is a hollow muscular organ that stores urine. The abnormity of detrusor excitability is one of the essential causes of bladder dysfunction and also the main field of our scientific research. At present, it is still not clear about whether detrusor has spontaneous excitability and the regulation of it. In our previous work, we found several interesting phenomenons: first, all the strips isolated from bladder exhibit spontaneous contraction activity under certain tension load, and the unstable strips will develop spontaneous contraction under little tension load; second, when under the same tension load, the frequency of unstable detrusor strips increases more significantly than that of normal detrusor; third, the spontaneous contraction is little affected by neural factors. These phenomenons indicate that the spontaneous contraction of detrusor strips may not be neurogenic, and the detrusor should have the ability of generating spontaneous excitability itself, and so, what is the pacemaker cell in bladder?With this question, it is naturally for us to think that the bladder smooth muscle cells may be the pacemaker cells. In the past several years, we have done some research work about the excitability of detrusor tissue at the level of bladder smooth muscle cells. Our results show that there are many factors that have close relationship with detrusor excitability, including the ultrastructure of smooth muscle cells, the receptor expression, the phenotype transformation of smooth muscle cells and the change of gap junction intercellular communication. But all the results can not show that the bladder smooth muscle cells are the origin the spontaneous excitability. In the year of 2001, Sui found that spontaneous potential can only be recorded in few cells, and most of the other cells can not. If the spontaneous potential origins from bladder smooth muscle cells, the spontaneous potential should be recorded in most of the cells. And so the bladder smooth muscle cells should not be the origin of the spontaneous excitability, and there should be some other cells that can generate spontaneous excitability. Recently, more and more attention has been paid to the interstitial cells of Cajal (ICC).The physiology of a number of smooth muscle tissues has been much enhanced by the study of a population of specialized cells first described in the gastrointestinal tract by Cajal. Interstitial cells of Cajal (ICCs), which are found throughout the gut, are now known to be the origin of pacemaker signals that underlie its spontaneous activity and they have a major role in the transmission of signals from enteric neurons to smooth muscle cells (SMCs).ICC-like cells have also been identified in many smooth muscle tissues, such as portal vein, ureteropelvic junction and urethra etc. Bladder is also a muscular organ that made up by smooth muscle tissue, and so we guess that there may be ICC-like cells in detrusor tissue, and these cells may be the pacemaker cells of bladder. To confirm this guess, in our previous researches, we have done some investigations on the ICC-like cells in detrusor tissue, and found that ICC-like cells do locate in guinea pig bladder and underlies spontaneous electricity potential. These results suggest that the cells have the electrophysiological characters of pacemaker cells, and they can be the candidate pacemaker cells in bladder.The organs that have been proved to have pacemaker activity usually have two characters: pacemaker cells and the transfer of pacemaker potential. Whether in heart or gastrointestinal tract, the number of muscle cells is much more than that of pacemaker cells, and so there must be some way to transfer pacemaker potential, which is essential for the synchronous contraction of muscle tissue. The results of histological research show that , in heart, the pacemaker is sinuatrial node, and intercalated disk is the structure that mediates the transfer of spontaneous excitability. And in gastrointestinal tract and ureter, the way for pacemaker potential to be transferred is gap junction. In our past research, we also found that there were gap junctions between detrusor cells, and in unstable bladder, the number of gap junction increased significantly, which make it possible that spontaneous excitability can be transferred through gap junction easily.What we talk about above show that the detrusor itself has spontaneous excitability,and there are the cells that can generate spontaneous excitability and the channels that can be used to transfer exctitability in bladder. And then, whether there are pacemaker activity in bladder? Where is the possible pacemaker site? What is the relationship between ICC-like cells and pacemaker site? This study is of great significance. First, it will help us to know whether the detrusor itself has spontaneous excitability. Second, it will help us to get an essential comprehension about bladder physiology. Third, it is helpful to reveal some essential pathogeny of some disease of bladder dysfunction. And at last, it will offer us a new field about the series research on detrusor excitability.To finish this study, we plan to do some works as following: first, by investigation of the variance of detrusor excitability in different locations of bladder or between normal bladder and unstable bladder, to explore the possibility that bladder has pacemaker site and its possible location; second, at the base of the results of part one, by the dysfunction of different areas of bladder, to explore their effects on bladder function and the possible functional pacemaker site in bladder; third, by the method of immunofluorescence histochemistry, to explore the presence of ICC-like cells in rat bladder and its relationship with nerve fibres; at last, by investigation of the distribution of ICC-like cells and its innervation in normal bladder and unstable bladder, to explore the correlation between ICC-like cells and detrusor excitability,Materials and methods: Female SD rats of 2～3 months , weighing from 220-280g were used. Proximal urethra was partial ligated to produce the models of partial bladder outlet obstruction (BOO). Intravesical pressure was measured 6 weeks later. Rats were divided into DI group and normal control group. The detrusor excitability was investigated by the test of strips contraction and the record of myoelectric potential. Fresh detrusor strips were used in muscle strips experiment. The myoelectric potential was recorded by optimized Ag-Cl electrode. And then by manual blockade, the function of potential pacemaker site was investigated. Immunofluorescent was used to investigate the presence and distribution of ICC-like cells and the distribution of nerve fibres in rat bladder. And then the correlation between ICC-like cells and detrusor excitability or between the ratio of nerve fibre to ICC-like cells and detrusor excitability was investigated. At last, the effects of Glevic, one specific blocker of c-kit receptor, were investigated on the contraction and myoelectric potential of detrusor strips.Results:1. The contraction frequency and amplitude of the strips harvested from different locations of bladder is different. The contraction frequency and amplitude of the strips obtained from the dome and triangle are higher than that obtained from the body and base, and in unstable bladder, the contraction frequency and amplitude of the strips from all the locations are significantly higher than that in the corresponding locations of normal bladder, and the strips from the dome is the highest.2. The myoelectricity potential amplitude of the strips obtained from different locations of bladder is different. The myoelectricity potential amplitude of the strips obtained from the dome and triangle are higher than that from the body and base, and in unstable bladder, the myoelectricity potential amplitude of the strips from all the locations are significantly higher than that in the corresponding locations of normal bladder, and the strips from the dome is the highest. The myoelectricity potential frequency of all the locations of bladder is similar, whether normal bladder or unstable bladder.3. When block the dome, the amplitude of both the micturition contraction or spontaneous contraction decrease significantly, including normal bladder and unstable bladder;4. When block the triangle, the micturition contraction disappears while the spontaneous contraction amplitude of normal bladder increased a little.5. When block the body or base, the spontaneous contraction is little affected but the amplitude of micturition contraction decrease.6. During the filling period, the spontaneous contraction is not accompied or only accompied by weak nerve impulse, and when cut the double pelvic nerve, in both the normal bladder and unstable bladder, the micturition contraction disappear, but the spontaneous contraction is sill present.7. ICC-like cells do locate in rat bladder, and mainly locate in sub-mucous membrane, along the longitude of smooth muscle bundles, between smooth muscle bundles or along the blood vessels; and there are more ICC-like cells in unstable bladder than that in normal bladder, and the cell net is more obvious in unstable bladder than that in normal bladder.8. The density of ICC-like cells is different in different locations of rat bladder. There are more ICC-like cells in the dome and triangle than that in the lateral and base, and in unstable bladder, the density of ICC-like cells in dome is significantly higher than that in other locations, and then the triangle, and there are no difference between the body and the base. 9. The density of nerve fiber is similar in all the locations of bladder, whether normal bladder or unstable bladder, but it decreases significantly in unstable bladder than that in normal bladder.10. The ratio of nerve fibre to ICC-like cells is different in different locations of bladder. The ratio in the dome and triangle is significantly lower than that in the body and base. In unstable bladder, the ratio decreases significantly in all the locations, the ratio in the dome is the lowest.11. The amplitude of the myoelectricity potential or strips contraction decreases significantly after Glevic was added. Conclusion:1. The excitability is different in different locations of bladder, which indicates there may be pacemaker site in bladder.2. The variance of excitability in different locations of bladder or between normal bladder and unstable bladder and results of functional research show that the triangle may be the"neurogenic pacemaker site"and the dome may be the"myogenic pacemaker site".3. The ICC-like cells do locate in rat ladder, most of the cells locate in sub-mucous membrane, along the longitude of smooth muscle bundles, between smooth muscle bundles or along the blood vessels, and the cells in different locations may play a different role;4. There are two existent fashions of ICC-like cells in rat bladder: single or conjuncted closely each other. In normal bladder, most of the ICC-like cells are single, and in unstable bladder, there are more ICC-like cells and the cell net is more obvious .The different exist fashion may has some relationship with their function.5. There is a strong positive correlation between the density of ICC-like cells and detrusor excitability, and the strips contraction and myoelectricity potential can be affected by Glevic obviously, which indicated that there may be close relationship between ICC-like cells and the function of detrusor.6. The density of nerve fibre decreases significantly in unstable bladder and there is a strong negative correlation between the ratio of nerve fibre to ICC and detrusor excitability, which indicated that the excitability of isolated detrusor strips may be myogenic. |
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