Fig. 3

Vacuoles may originate from membrane invaginations. a. Serial sections stained for laminin with a section thickness of 10 µm demonstrate how invaginations apparently terminate in three vacuoles (red arrowheads), bar is 50 µm. b. Serial sections demonstrate how invaginations (red line) from opposite sides meet at a vacuole (red oval), bar is 50 µm. c,d. electron microscopy images demonstrating vacuoles with no content and plasma membrane (PM, black arrows) separating sarcoplasm from vacuole (inserts). e,f. Low power electron microscopy image demonstrating different vacuoles, one of which is connected to the outside of the myofiber by an invagination (white arrows). The white box in panel E refers to panel F, and the box in panel F refers to panel G. g. An invagination ends in “fingers” with caveolae (white arrows) along the plasma membrane (black arrows)