Expanded vacuoles and intussusception in male β3-null coronary capillaries. Transmission electron micrographs show that coronary capillaries from male β3-null mice contain single endothelial cells with expanded vacuoles (A-D) that, like pockets formed by interacting filopodia, are consistent with angiogenesis by division of existing vessels. Some vessels have a limited luminal area and appear to be composed of a single endothelial cell (B), because cell-cell junctions are not visible. Although less frequent, some endothelial cells have luminal processes that extend across the lumen, resembling angiogenesis by intussusception (E). Asterisks indicate expanded vacuoles; arrows, intussusception. Bar = 500 nm.