In cardiac muscle, which junction in intercalated discs provides electrochemical coupling?

• A. Desmosomes
• B. Gap junctions
• C. Hemidesmosomes
• D. Tight junctions

Answer: (B)

Electrochemical coupling in cardiac muscle is achieved by gap junctions within intercalated discs. These channels, formed by connexin proteins, create direct cytoplasmic connections between adjacent cardiomyocytes, allowing ions such as Na+, K+, and Ca2+ to flow rapidly from one cell to the next. This enables quick, coordinated spread of action potentials and synchronized heart contractions. Desmosomes and adherens junctions provide mechanical linkage to resist the forces of contraction, but they don’t permit ion flow. Hemidesmosomes anchor cells to the basement membrane, and tight junctions seal spaces between cells without mediating electrical coupling. So the junction responsible for electrochemical coupling is the gap junction.