<prompt> 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 became fluorescent. The most likely explanation for this observation is the presence ofGap junctionsIP3 receptorsTransverse tubulesDesmosomes  <response>: Gap junctions are pores composed of paired connexons that allow the passage of ions, nucleotides, and other small molecules between cells.Ref: Guyton; 13th edition 