RESUMO
The morphometry of the intramembranous particles (IMP) of the dog sinus node cells was studied with freeze-cleaved specimens under H-500 electron microscope. The photographs of IMP of the P cells and transitional cells were analysed with imaging analytical system (IBAS Ⅰ+Ⅱ type). The results are as follows. The mean area of IMP: on PF and EF faces of P cells are 25.800nm~2 and 17.816nm~2. The mean values of IMP on PF and EF faces of the transitional cells are 46.041nm~2 and 88.633nm~2. The averages of the perimeter of IMP on the PF and EF faces of P cells are 20.735 nm and 18.078 nm, respectively. And those of the transitional cells are 28.780 nm and 43.901 nm. The diameters of circles of IMP of PF and EF faces of P cells are 5.220 nm and 4.402 nm. Those of PF and EF faces of the transitional cells are 7.010 nm and 10.476 nm. The mean values of form factor of IMP on PF and EF faces of P cells are 0.653 and 0.643, and those of transitional cells are 0.627 and 0.573. The mumbers of IMP are 1325/?m~2 and 345/?m~2 on PF and EF faces of P cells, and the mumbers of IMP of the transitional cells are 3225/?m~2 on PF face and 590/?m~2 on EF face.