Abstract
Electrical synapses are formed by two unrelated gap junction protein families, the primordial innexins (invertebrates) or the connexins (vertebrates). Although molecularly different, innexin- and connexin-based electrical synapses are strikingly similar in their membrane topology. However, it remains unclear if this similarity extends also to more sophisticated functions such as long-term potentiation which is only known in connexin-based synapses. Here we show that this capacity is not unique to connexin-based synapses. Using a method that allowed us to quantitatively measure gap-junction conductance we provide the first and unequivocal evidence of long-term potentiation in an innexin-based electrical synapse. Our findings suggest that long-term potentiation is a property that has likely existed already in ancestral gap junctions. They therefore could provide a highly potent system to dissect shared molecular mechanisms of electrical synapse plasticity.
Highlights
Electrical synapses formed by gap junction channels enable the direct spread of electrical current between coupled cells in vertebrates and invertebrates[1]
Comparable data are still lacking for innexin-based electrical synapses[19], suggesting that such higher forms of plasticity might constitute a functional difference between connexin- and innexin-based electrical synapses and that this difference was critical in the evolution of the modern connexins
We unequivocally and for the first time demonstrate that innexin-based electrical synapses are capable of a sophisticated form of plasticity that can underlie learning and memory
Summary
Electrical synapses formed by gap junction channels enable the direct spread of electrical current between coupled cells in vertebrates and invertebrates[1]. Basic functional features of connexin- and innexin-based electrical synapses are remarkably similar. They are both known to be regulated by pH14, Calcium, transmembrane voltage or transjunctional voltage[15,16,17,18] and respond to neuromodulators[19,20,21,22,23,24,25,26,27,28,29,30]. We show that it is possible to directly measure the gap junctional currents between the electrically coupled Retzius (R) cells in the nervous system of the leech (Hirudo medicinalis) and provide what seems to be the first direct demonstration of activity-dependent gap junction plasticity in an innexin-based electrical synapse
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