| The brain-gut axis, consisting of central nervous system (CNS), autonomicnervous system(ANS) and enteric nervous system(ENS), affects gastrointestinalmotility. Gastrointestinal smooth muscle cell (SMC) has rhythmic contractions,which is characterized by slow wave (SW). Research suggests that ICCs are thepacemaker cells of the smooth muscles’ slow wave, which can be divided intofour types according to their positions. IC-MY, which is located between thecircular muscles and longitudinal muscles is proved to be major pacemaker cellthat generates gastrointestinal rhythmic slow wave. After inhibition of theinhibitory neurotransmitter of autonomic nervous system, nitric oxide synthase(NOS) on ICCs will release nitrogen monoxidum (NO) which suppressesgastrointestinal motility. Hyperpolarization-activated cyclic nucleotide-gatedchannel (HCN), which is unique to mammals, has intrinsic activity of Ih and isproved to be a slow wave pacemaker channel. The activity of cardiac pacing andneural activity often depend on HCN. HCN can be divided into four subtypes,but there is almost no research on the distribution of HCN1in gastrointestinal system. The laboratory has found a specific distribution ofhyperpolarization-activated cyclic nucleotide-gated channel—HCN1whichmakes self-discipline rhythms in the rat gastrointestinal tract’s ICCs byobserving the ultrastructures and using immunofluorescence double labeling.Moreover, expression goes up when rats have a stable gastrointestinal tractperistalsis, which indicates that HCN1is important to make ICCs take aspontaneous rhythm. The contraction of isolated muscle strips reducessignificantly, when the strips are given ZD7288, HCN1specific blocker, toblock HCN1’s function, which proves that HCN1may be the original ionchannel of gastrointestinal dynamic pacing. Ischemic changes of thegastrointestinal tract can cause obvious gastrointestinal motility disorders inpatients in clinical practice, but there is no clear report at present on theconnection between the mechanism responsible for gastrointestinal motilitydisorders and the existence of HCN1. This research sets up an ischemia modelof rats’ gastrointestinal tract, measures the expression of HCN1in theexperimental group and normal reference group, and observes the distribution ofHCN1, its coexistence with neurotransmitter by double immunofluorescencelabeling and its change after gastrointestinal ischemia. The role of HCN1and itspossible mechanism in the process of gastrointestinal ischemia are expected tobe verified and serve as the theoretical basis for the treatment of gastrointestinalmotility disorders.Methods①Set up an animal intestinal ischemia model;②Detected changes of rats’EGG (electrogastrography) and MMC (migrating myoelectric complex) of smallintestine by using electrophysiological methods;③Identified the relationshipbetween changes of EGG and MMC, as well as changes of gastrointestinal electric activity according to the time that the model is established. Meanwhile,observed the changes of expressions of HCN1in different time byimmunofluorescence methods to sift typical period out and analyzed whetherthere is a correlation between HCN1’s expression and MMC’s changes of smallintestine.④Used ZD7288, HCN1’s specific blocker, to block rat in the typicalperiod, observed changes of MMC after ischemia and verified the function ofHCN1.⑤Label HCN1with SP(substance P) and HCN1with CGRP(calcitoningene related peptide) by immunofluorescence double labeling to verify thatHCN1coexists with some brain-gut peptides in gastrointestinal ischemicsituations.⑥Given rats of the typical period the intervention of inhibitoryneurotransmitter NO, then observed the expressions of SP and CGRP and detectthe concentrations of them in tissue and plasma, along with the changes ofMMC of small intestine.Results1. Gastrointestinal ischemic changes can lead to changes of gastrointestinalmotility. After an incomplete ischemia, gastrointestinal motility is lowering andunder a disorder in early ischemia. But the motility will improve gradually astime goes on. Through this study, EGG and MMC of small intestine are found tobe in a mess and in a low state at the beginning of intestinal ischemia. They arealso proved to be in a stable state five days later and recover seven days later.Correlation analysis shows a linear relationship between expressions of c-kit andHCN1while the ischemic time is extending, which suggests that ischemicchanges of gastrointestinal tract can lead to changes of gastrointestinal motilityand gastrointestinal motility disorder caused by ischemia can recover graduallywith the gradual recovery of functions of c-kit and HCN1.2. HCN1expresses in gastrointestinal mucosa and smooth muscle gap and tends to be positive after double libeling with c-kit. Its expressions increasesignificantly under the ischemic conditions of the gastrointestinal tract. WhenHCN1’s function is blocked, gastrointestinal motility disorder, as a result ofischemic changes, will reduce remarkably as the pacing role of HCN1is blocked,which further proves that HCN1plays the role of original pacing ion channel.Furthermore, the research finds that some gastrointestinal hormone improvinggastrointestinal motility such as SP and CGRP coexists with HCN1, which willnot be affected when the function of HCN1is blocked. Therefore, it can beconcluded that SP and CGRP may play important roles in mediation of HCN1.3.When given brain-gut peptide NO of exogenous inhibition ofgastrointestinal motility, expressions of HCN1, SP, and CGRP all decrease,which indicates that the excitatory neurotransmitter and the inhibitoryneurotransmitter work together in making HCN1play the role of original pacingion channel. Moreover, when inhibitory neurotransmitter’s function enhances,gastrointestinal motility will obviously be inhibited.ConclusionExpressed in gastrointestinal mucosa and smooth muscle gap, HCN1’sexpressions increase significantly under the ischemic conditions ofgastrointestinal tract. At the same time, neurotransmitter such as SP and CGRPalso expresses in the myenteric plexus and increases compensatorily afterischemia while decreases when given NO, which indicates that HCN1may playan important role in regulating gastrointestinal motility and may be the originalpacemaker ion channels. |
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