Figure 8.

Intracellular syntaxin 4–positive organelles can be observed under normal extracellular calcium conditions in cells that are not within a monolayer. MDCK cells expressing syntaxin 4 were grown for 16 h in medium containing a normal calcium concentration. The medium for A–D contained 5% FCS, whereas the medium for E and F was serum-free. Cells were costained for syntaxin 4 (left column) and gp135 (right column). Syntaxin 4 frequently localizes to intracellular organelles in single cells (C) as well as in cells at the periphery of a colony (A, arrow) regardless of the presence of serum. In contrast, syntaxin 4 is mostly restricted to the plasma membrane in cells in the midst of a colony. Prominent intracellular gp135-positive VACs are frequent in cells grown in the absence of serum (E and F, arrows) but rare when serum is included. Bars, 5 μm.