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Synaptic Transmission from Horizontal Cells to Cones Is Impaired by Loss of Connexin Hemichannels

Figure 7

Model for ephaptic feedback.

(A) Schematic drawing of the cone synaptic terminal. HC, horizontal cell; BC, bipolar cell; ICa, cone Ca2+-current; Vext, potential in the synaptic cleft. (B) The feedback model formulated by Fahrenfort et al. [6] was used to evaluate the effect of changes in voltage dependence of horizontal cell hemichannels. Here we will give a short description of the main features, for a full description see Fahrenfort et al. [6]. The model consists of a simple resistive network. The model was used to evaluate the relation between the horizontal cell membrane potential (VHC) and the change in extracellular potential (Vext) with different numbers of hemichannels in the horizontal cell membrane. Vext is the potential in the synaptic cleft, VHC is the horizontal cell membrane potential, ghemi is the hemichannel conductance, gGlu, tip is the glutamate conductance at the tips of the horizontal cell dendrites, gGlu, neuropil is the glutamate conductance of the horizontal cell dendrites in the neuropil, gK, is the potassium conductance of horizontal cells and EK is the equilibrium potential for potassium. [Glu] is the Glutamate-concentration in the synaptic cleft. ICa is the cone Ca2+-current; gext is the conductance of the extracellular space in the synaptic complex.

Figure 7

doi: https://doi.org/10.1371/journal.pbio.1001107.g007