Ephaptic interactions within a chemical synapse: hemichannel-mediated ephaptic inhibition in the retina.
The two best-known types of cell-cell communication are chemical synapses and electrical synapses, which are formed by gap junctions. A third, less well known, form of communication is ephaptic transmission, in which electric fields generated by a specific neuron alter the excitability of neighboring neurons as a result of their anatomical and electrical proximity. Ephaptic communication can be present in a variety of forms, each with their specific features and functional implications. One of these is ephaptic modulation within a chemical synapse. This type of communication has recently been proposed for the cone-horizontal cell synapse in the vertebrate retina. Evidence indicates that the extracellular potential in the synaptic terminal of photoreceptors is modulated by current flowing through connexin hemichannels at the tips of the horizontal cell dendrites, mediating negative feedback from horizontal cells to cones. This example can be added to the growing list of cases of ephaptic communication in the central nervous system.
The Netherlands Ophthalmic Research Institute, Royal Netherlands Academy of Arts and Sciences, Meiberdreef 47, 1105 BA Amsterdam, The Netherlands. m.kamermans@ioi.knaw.nl
Maarten
M
Kamermans
Iris
I
Fahrenfort
D000818:Animals; D017630:Connexins / Q000502:physiology; D005246:Feedback / Q000502:physiology; D006801:Humans; D007395:Interneurons / Q000502:physiology* / Q000648:ultrastructure; D007473:Ion Channels / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology* / Q000648:ultrastructure; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology* / Q000648:ultrastructure; D013569:Synapses / Q000502:physiology*
D017630:Connexins; D007473:Ion Channels