| Background and objective: Sick sinoatrial node syndrome (SSS) is a common cardiovascular disease which is greatly harmful to human health. To elucidate the pathogenesis of SSS and to find out the possible measures of prevention and radical cure is important in cardiovascular field. Gap junction whose molecular basis is made up of connexin (Cx) is one of the specialized intercellular connection manners. There are many kinds of Cxs in myocardial cells which are crucial for guiding electric and chemical signals amongst myocardial cells and guarantee normal electric-machinery coupling to maintain normal cardiac function. There are different connexins in different mammals as well as one of mammal with different connexins. There are three kinds of connexins (Cx45, Cx43 and Cx40) in mammalian heart. Up to date, there are many reports on the lesions of connexins in myocardial diseases especially arrhythmias, but there are few reports on connexin changes in rabbit sinoatrial node cells when damaged. The purpose of our investigation is to observe the dynamic regulation of electrophysiologic function, cell morphologic changes and expression of connexin of rabbit as damaged by formaldehyde wet dressing method, and discuss the feasibility of establishing the acute damage model of rabbit sinoatrial node by formaldehyde wet dressing method. Methods: Sixty rabbits were randomly divided into 6 groups (10 for each group): the control group and groups of after operation 2h, 1w, 2w, 3w and 4w. The rabbits were anesthetized with sodium pentobarbital and the chest was opened through the right lateral line away 2 to 3 millimeters from the sternum. The sinoatrial node area of rabbits was damaged by 20% formaldehyde wet dressing in the experimental groups and by saline wet dressing in the control group. 3F tetra-electrode catheter was inserted into the right atrium through right external jugular vein in the control group and 2h group after wet dressing for 2h, in the other groups at the corresponding times of re-operation respectively; electrocardiogram of body surface and endocardium were recorded synchronically; then the right atrium was stimulated, and sinus node recovery time (SNRT), corrected SNRT and sino-atrial conduction time (SACT) were measured respectively. The rabbits were sacrificed after electrophysiological study and the tissue of SAN was cut and fixed respectively. Light and electronic microscope was used to examine the pathological changes of SAN cells. Apoptosis of sinoatrial node cells was detected by TUNEL staining and expression of Cx45 and Cx43 detected by immunohistochemical staining.Results: 1. The heart rate (HR) and cardiac rhythm of the control group dressed by saline didn't change distinctly while that of the experimental groups dressed by formaldehyde were slower than before dressing. The change of HR in experimental groups was significant compared to that of control group (P<0.05). Sinus arrest, junctional escape rhythm and atrial fibrillation were present in 80% rabbits of experimental groups. 2. The SNRT,corrected SNRT and SACT of experimental groups were all significantly longer than those of the control group (P<0.05) . 3. There were cell swelling, granulocytic cell infiltration and focal necrosis found by light microscopy in experimental groups at the early stage, and late part of collagen fiber proliferation was found. Under electron microscope, the sinoatrial nodal matrix became sparse and lightly-stained, and mitochondria swelling, cristae disorganization or break, endoplasmic reticulum disintegration or break as well as the nucleolus splitting was also found in experimental groups. 4. There were few TUNEL positive cells in sinoatrial node of rabbits in the control group while there were lots of TUNEL positive cells in sinoatrial nodes of all experimental groups. The ratios of apoptosis in all experimental groups were significantly higher than that of the control group (P<0.01). 5. The Cx45 of sinoatrial node cells of rabbits expressed in the center of the sinoatrial nodal area wa...
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