Gap Junctions and Electrical Synapses

Gap junctions are common intercellular organelles that join the interiors of functionally coupled cells. Most neurons express both the machinery for chemical transmission and the proteins that allow electrical transmission, that is, the family of gap junction proteins, connexins. Connexin Cx36 is the form at most mammalian electrical synapses, but some neurons express other connexins, and Cx36 is more widely distributed than initially thought. Electrical synapses mediate neuronal synchronization as well as lateral spread and forward transmission of information. Both chemical and electrical synapses can transmit graded potentials. In single neurons, gap junctions may permit GABAergic cells to be excitatory as well as inhibitory and to synchronize with others more precisely than possible with inhibition alone. Gap junctional communication can be modified by heterosynaptic inputs operating through G-protein-coupled receptors and kinases. Formation of gap junctions in general is highly specific, but the controls of specificity are not well understood.