Gap junctions in many tissues can be opened or closed in response to extracellular or intracellular signals.

The neurotransmitter dopamine, for example, reduces gap-junction communication between certain neurons in the mammalian retina when secreted in response to an increase in light intensity.

This reduction in gap-junction permeability alters the pattern of electrical signaling and helps the retina switch from using rod photoreceptors, which are good detectors of low light levels, to cone photoreceptors, which detect color and fine detail in bright light.

Gap junctions are dynamic structures that, like conventional ion channels, are gated: they can close by a reversible conformational change in response to extracellular or intracellular sign als . The permeability of gap junctions decreases within seconds, for example, when the intracellular Ca 2+ concentration is raised.