This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pharmacology
A single cell within a culture of freshly isolated cardiac muscle cells is injected with a fluorescent dye that cannot cross cell membranes. Within minutes, several adjacent cells become fluorescent. The most likely explanation for this observation is the presence of 
Select and explain. 
A. Gap junctions, B. IP3 receptors, C. Transverse tubules, D. Desmosomes
A: Gap junctions
Answer: A: Gap junctions 
Explanation: Gap junctions are pores composed of paired connexons that allow the passage of ions, nucleotides, and other small molecules between cells. Ref: katzung 12 th ed.