Hypertrophic smooth muscle. II. Sarcoplasmic reticulum, caveolae and mitochondria.

The cytological features of hypertrophic smooth muscle cells are investigated in the small intestine of the guinea pig in which a hypertrophy is induced by an experimental stenosis. By freeze-fracture the cell membrane appears richer in intramembrane particles than that of control muscle cells, whereas the number of caveolae per unit surface of cell membrane shows little or no change (16--19 caveolae micron-2). In the sarcoplasm there is a conspicuous increase of both smooth and rough sarcoplasmic reticulum; extent was measured by surface and by volume. Unusual forms of reticulum also appear. Mitochondria are reduced (in percentage volume) to about half the control value.