Blood vessel phenotype in male β3-null mice is confirmed by scanning electron microscopy. Coronary capillaries from adult wild-type mice (A-B) have a smooth luminal surface consistent with images acquired using TEM. Freeze-fractured samples prepared for SEM reveal filopodia extending into the vessel lumen (C-D) or across the lumen to make adhesive contact with the opposite wall (E). Luminal divisions are visible, which may represent the expanded vacuoles observed via TEM (F). Arrows indicate filopodia; asterisk, expanded vacuole. Bar = 500 nm.