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Gap junctions are a specialized intercellular connection between a multitude of animal cell-types. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulated gate between cells. One gap junction channel is composed of two connexons (or hemichannels), which connect across the intercellular space. Gap junctions are analogous to the plasmodesmata that join plant cells. Gap junctions occur in virtually all tissues of the body, with the exception of adult fully developed skeletal muscle and mobile cell types such as sperm or erythrocytes.
Upon entrance of the K+ ion to the selectivity filter from the cytoplasmic side, the outermost K+ exits the channel to the extracellular solution. The jumps of ions between these sites and the sequence of multi-ion configurations involved in permeation are described thoroughly in here.+ channels are membrane proteins that allow rapid and selective flow of K+ ions across the cell membrane, and thus generate electrical signals in cells. Voltage-gated K+ channels (Kv channels), present in all animal cells, open and close upon changes in the transmembrane potential.