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Katherine Fehlhaber, Anurima Majumder, Kimberly Boyd, Nikolai Artemyev, Alapakkam P Sampath; UNC119 expression in rods is required to maximize the sensitivity of rod bipolar cells. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1716.
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© ARVO (1962-2015); The Authors (2016-present)
UNC119 is a binding partner of G-protein α subunits and has been shown to be important in G-protein trafficking, particularly in transducin trafficking in rods. UNC119 is highly expressed in rod spherules and inner segments. However, its role in signal transmission to bipolar cells remains unclear. A putative synaptic function is suggested based on the interactions of UNC119 with CaBP4, a Ca2+-dependent modulator of the voltage-gated calcium channel Cav1.4, and RIBEYE, a major component of synaptic ribbons.
Signal transmission between rods and rod bipolar cells was assessed by making whole-cell voltage clamp recordings from rods (Vm = -40mV) and rod bipolar cells (Vm = -60mV) in dark-adapted retinal slices from UNC119+/- (control) and UNC119-/- mice. Light-evoked responses were generated by a brief flash (10ms) from a blue LED (λmax ~ 470 nm).
The size of light-evoked responses from rod photoreceptors displayed a similar dependence on flash strength in both control and UNC119-/- mice, indicating the outer segment current was unaffected by the lack of UNC119. However, UNC119-/- rod bipolar cells displayed ~5-fold desensitization compared to control. Additionally, while the time course of photoresponses were similar in control and UNC119-/- rods, UNC119-/- rod bipolar cells displayed response acceleration.
Our results suggest that UNC119 plays a crucial role in synaptic transmission between rods and rod bipolar cells. In the dark-adapted retina these effects appear to be directly on synaptic release, since the rod photocurrents are unchanged in UNC119-/- rods. Future experiments will determine the role of UNC119 in modulation of Cav1.4 activity and during light-dependent translocation of transducin.
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