Cytofluorometric nuclear DNA determinations on the atrioventricular nodal cells in human hearts

In the human heart, it is well known that the polyploidization of working heart-muscle cells increases in proportion to increases in heart weight, but there has been no investigation of the process of polyploidization in the specialized heart-muscle cells of the cardiac conduction system which have a nerve-like function. In order to investigate the process of polyploidization in these cells, the nuclear DNA content of atrioventricular nodal cells was measured using cytofluorometry. Tissue samples taken from autopsied hearts without arrhythmias were embedded in paraffin blocks after Carnoy fixation. Blocks containing the atrioventricular conduction system were cut according to the serial sectioning method of Lev et al. The compact atrioventricular nodes were removed from thick paraffin sections (150 micron) under a stereomicroscope. The cells were then isolated by enzyme digestion and ultrasonic treatment. Smears of the isolated cells were double stained with azocarmin-G and acriflavine-Feulgen. Cytofluorometric DNA determinations of the DNA content of atrioventricular nodal cells were performed. Atrioventricular nodes were found to be composed of a large number of diploid cells and a small number of tetraploid cells. No octaploid cells were found. These findings reveal that the process of polyploidization in atrioventricular nodal cells is different from that found in working heart-muscle cells.