Effects Of Rapid Atrial Pacing-on Atrial Remodeling And The NPR/PGC/cGMP Signaling Pathway In Rabbits

Atrial fibrillation (AF) is one of the common clinical arrhythmia, which might seriously affect human health and the quality of human life, but its exact pathogenesis is not clear. Atrial structural, electrophysiological remodeling and abnormal distribution of calcium ion may lead to multiple reentrant wave in atrium, and thus promote the maintenance of atrial fibrillation. CGMP regulation of cardiac function as intracellular second messenger, its intracellular levels by guanylate cyclase activation and formation process and two process is the decomposition of PDE to achieve the dynamic balance in order to maintain the proper intracellular concentrations. The clinical study showed that,, higher ANP and BNP concentrations in blood during atrial fibrillation and atrial fibrillation, and related to the course of disease, but the changes in atrial tissue in atrial fibrillation atrial remodeling and NPR/pGC/cGMP and its pathophysiology effect is not clear. Therefore, we studied the structural changes of atrium after rapid atrial pacing, ion channel and the signal pathway of NPR/pGC/cGMP, in order to clarify the mechanisms of atrial remodeling in AF.Methods: Rabbits model of rapid atrial pacing were establisded. The RM6240physiological signal acquisition system was used. The surface limb lead electrocardiographies were recorded at the same time. Atrial structural changes were observed by light and transmission electron microscopy, it is found that rapid pacing tructure effects atrial sarcoplasmic reticulum and mitochondria ultrastructure;on this basis, using RT-PCR, Western blotting and spectrophotometric method was used to detect PO and P8expression and activity of the Ca2+channel, L type GRP78,JNK and CHOP and mitochondrial mPTP opening degree, from the relationship between the molecular level comparison of structural remodeling and electrical remodeling; PO were detected by radioimmunoassay (control group), PI, P2, P4and P8the level of serum ANP; expression using immunohistochemistry and Western blot detection of atrial natriuretic peptide receptor; at the same time, effects of rapid atrial pacing on the activity of pGC and indirect cGMP concentrations were observed in atrial tissue was determined by ELESA method; the mechanism of rapid atrial pacing induced changes in cGMP concentration and its relation to the atrial remodeling.Results:1.The right external jugular vein puncture implanted electrodes, ECG detection in vitro electrophysiological changes and electrode positioning in rabbits with rapid atrial pacing the right atrium model, stable and reliable, easier to simulate the occurrence of atrial fibrillation2. the changes of atrial tissue structure, rapid atrial pacing at different moments of light microscopy and transmission electron microscopy results:1. HE staining, the atrial muscle fibers in a long strip shape, a branch, the branch is connected into a network. Nuclei were oval, located in the central atrium muscle fibers, muscle fibers visible light and dark stripes, and the control group (PO) and pacing at different time (P1, P2, P4, P8) had no obvious change between groups. Observation of transmission electron microscopy (P0, P1, P2, P4, P8) ultrastructure, visible dilatation of sarcoplasmic reticulum, mitochondria swelling, deformation, ridge arranged in disorder, disappear, massive vacuolization and glycogen accumulation was, myofilament dissolved, nuclear membrane rupture, depression, with the stimulation time of injury, P8more obvious. Therefore, this study selected PO and P8atrial tissue was studied3.Using RT-PCR, Western method of blot and spectrophotometer to detect the change of L expression and activity of PO and P8, Ca2+channels in atrial tissue GRP78, CHOP and JNK. and mitochondrial mPTP opening degree, results can be observed, the L-type calcium channel subunit alpha1expression of mRNA had no significant change in the fast paced P8an increase in GRP78and CHOP; the P8expression in atrial tissue, compared with PO up-regulated the expression of P8, atrial tissue of phosphorylated JNK were significantly increased, compared with PO were up-regulated; the spectrophotometer combined determination of PO and P8in atrial tissue of mPTP opening degree swelling buffer induction method, in the induction of200umol/L Ca2+next, P8atrial muscle mitochondrial absorbance decreased rapidly, PO and P8respectively, suggesting that P8atrial muscle mitochondrial mPTP and PO were increased compared to open.4.Radioimmunoassay technique for determination of ANP concentration PO, PI, P2, P4and P8in the blood of rabbits, the results were0.239±0.0350.027and0.386±0.086μg/L (P<0.01); the concentration of ANP pacing group1h in plasma of rabbits with pacing time highest, ANP concentration decreased, but were higher than P0.5. Determination of P0, P1, P2, P4and P8in atrial tissue cGMP concentration by ELISA, cGMP concentration of P1results in atrial tissue was higher than that of P0, but with the stimulus duration decreased gradually, the level of cGMP in atrial tissue of P8below P0, with statistical significance (P<0.01).6.Determination of atrial natriuretic peptide receptors A and B6immunohistochemistry, Western blot combined with enzyme linked immunosorbent assay and the expression of guanylate cyclase activity, results P0and P8in atrial tissue expressed NPR-A and B receptors were observed in brown powder, particle size distribution, but its expression was not the difference of Western blot; NPR-A/B for further quantitative results also show, there was no difference between P0and P8; the indirect determination of pGC activity and ELISA binding membrane fragments, found the pGC activity of P8in atrial tissue was significantly lower than that in P0.Conclusion:1. Rapid atrial pacing in rabbits could simulate the arial remodeling of the early stage of AF. The results were stable and reliable. 2. In the early stage of rapid atrial pacing, the changes of sarcoplasmic reticulum and mitochondria structure were ealier than that of ion channel density.3.Rapid atrial pacing can induce mitochondrial membrane potential and endoplasmic reticulum stress and atrial remodeling of myocardial intracellular calcium abnormal distribution.4. ANP was involved in atrial remodeling of atrial fibrillation through NPR-A/pGC-cGMP pathway.5. In the early stage of rapid atrial pacing, early atrial cGMP concentration decreasing was caused by decreased pGC activity.6. In the early stage of rapid atrial pacing, the declining of cGMP concentration is one of the important mechanisms of atrial remodeling.7. Interference of NPR/pGC/cGMP may be a pharmacological target of prevention and treatment of atrial fibrillation induced atrial remodeling.