What is the role of gap junctions in epithelial tissue?

• A. They permit direct cytoplasmic exchange of ions and small metabolites, coordinating cell activity.
• B. They seal apical surfaces to prevent leakage between cells.
• C. They anchor cells to the basement membrane.
• D. They generate mucus on epithelial surfaces.

Answer: (A)

Direct cytoplasmic exchange of ions and small metabolites between neighboring epithelial cells coordinates tissue activity. Gap junctions form channels (connexons) that connect adjacent cell interiors, allowing ions, Ca2+, cAMP, IP3, and other small signaling molecules to pass between cells, usually up to about 1 kDa. This metabolic and electrical coupling lets epithelial cells respond in a coordinated way to stimuli and maintain homeostasis across the sheet, such as synchronized ion transport and calcium signaling waves. This function is distinct from tight junctions, which seal surfaces to prevent leakage, from anchoring junctions that attach cells to the basement membrane, and from mucus-secreting cells that produce mucus.