Communicating junctions, also called gap junctions or nexus, are present in a wide variety of tissues, including epithelia, smooth and cardiac muscle, and nerves. They are important in tissues in which activity of adjacent cells must be coordinated, such as epithelia engaged in fluid and electrolyte transport, vascular and intestinal smooth muscle, and heart muscle. A gap junction consists of an accumulation of transmembrane channels or pores in a tightly packed array. The pores in one cell membrane are precisely aligned with corresponding pores on the membrane of an adjacent cell, thus, as the name implies, allowing communication between the cells. The gap junctions allow cells to exchange ions, regulatory molecules, and small metabolites through the pores. The number of pores in a gap junction can vary widely, as can the number of gap junctions between adjacent cells.
Organized concentrations of integral membrane proteins form the gap junctions
Various procedures have been used to study gap junctions, including the injection of dyes, radiolabeled compounds, or electric current into cells and the measurement of these probes in adjacent cells. In dye studies, a
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