They allow any molecule to move across or any ion to move across, as long as it's not too large. So large substances such as proteins and polynucleotides and polysaccharides, these molecules cannot pass across gap junctions. Now, unlike these voltage gated and ligand gate on channels, which are only open for about a millisecond before being closed or inactivated, these gap junctions can be open anywhere from seconds to minutes. Now, voltage gated and ligand gate on channels connect the cytoplasm of a cell to the outside extracellular environment. But we see that these gap junctions actually connect two adjacent cells. And more specific, they transverse the membrane of these two adjacent cells and they connect the cytoplasm of one cell to the cytoplasm of that contiguous adjacent cell.