Ultrastructural morphometry of cultivated smooth muscle cells from normotensive and hypertensive rats

Cultivated aortic smooth muscle cells (SMC) derived from normotensive and hypertensive rats were analyzed by transmission electron microscopy and ultrastructural morphometry. SMC cultures obtained from hypertensive rats showed an increase in cell size and a higher percentage of large, often polynuclear cells. The stereological data of mitochondria, rough endoplasmic reticulum (RER) and secondary lysosomes were determined by measuring area according to the "Delesse principle". The organelle contents of small and large cells of each group were only slightly different. Significant changes were found between SMC from normotensive and hypertensive rats: The volume density Vv of mitochondria per unit cytoplasm volume was increased up to 48% in small and 50% in large SMC from hypertensive rats compared to those of control animals. The numerical density Nv of secondary lysosomes per unit cytoplasm volume was increased up to 68% in small and 267% in large SMC from hypertensive rats. The content of rough endoplasmic reticulum varied tremendously between the individual cells. All these stereological data represent relative parameters of cell organelles relative to the unit cytoplasm volume. Therefore the differences between the absolute values would be even higher since SMC from hypertensive rats are shown to have a higher mean cell size and volume. We conclude that the effect of experimental hypertension, resulting in an activation of SMC, persists even when the cells are transferred to in vitro conditions.