ABSTRACT
Objective To localize the sinoatrial node (SAN) of the newborn rabbits in vivo and cut it for purifying cultivation and study the morophologic characters of primary cultured pacemaker cells of SAN under light microscope and transmissional electron microscope. Methods Hearts of the newborn rabbits were embedded in paraffin for HE-staining and observed the location, form of SAN under optical microscope; SAN cells isolated from neonatal rabbits cultured and purified with the method of differential attachment and BrdU-treatment.Results SAN localized in the anterior wall of the superior vena cava and the posterior-lateral atrial wall.There was about 0.32 mm between its lowest point and sulcus terminalis. Three distinctly different types of cells were observed among the cultured cells of SAN: spindle, araneiform and polygon. The spindle cells covered the greatest proportion of the cultured cells of SAN (59.6%?7.3%). The frequency of spontaneous contraction of spindle cells was the highest among the constrcting cells (145 ?9)time/min. The results of ultrastructure observation showed that myofibrils and other organelles in spindle cells were poorly organized and significantly decreased in number compared with araneiform cells. There was no significant difference between araneiform cells isolated from SAN and from atrial muscle.Conclusion Among the cultured cells from neonatal rabbits SAN, the spindle cells are the pacemaker cells of SAN.