Which cell junction allows exchange of cytoplasmic molecules?

Gap junction forms tunnels that join the cytoplasm of two cells. Units called connexons lines up in the cell membrane of each cell that contributes to the gap junction. The subunit surrounds a channel of diameter 2nm and the channel of the connexion of one cell is continuous with the channel in the connexion of the adjacent cell at gap junction. This permit exchange of substance from one cell to the other. (REF: TEXTBOOK OF MEDICAL PHYSIOLOGY GEETHA N 2 EDITION, PAGE NO - 18)