Gap junctions are located in which membrane domain?

• A. Apical
• B. Laterally
• C. Basal
• D. All surfaces

Answer: (B)

Gap junctions form direct channels between neighboring cells, so they must be located where cell membranes are in close contact. In epithelial sheets, this happens in the lateral membrane domain, at the borders where adjacent cells meet. The apical surface faces the lumen and is usually sealed off from neighboring cells by tight junctions, while the basal surface faces the basement membrane; neither is a site for direct cytoplasmic continuity between cells. Hence, gap junctions are best located in the lateral membrane, enabling ions and small molecules to pass directly from one cell to its neighbor.