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Teresa Puthussery, Daniel B Yaeger, Roupen A Khanjian, Jacqueline Gayet-Primo; Localization and functional properties of Kv8.2-containing voltage-gated potassium channels in primate photoreceptors. Invest. Ophthalmol. Vis. Sci. 201657(12):.
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© 2017 Association for Research in Vision and Ophthalmology.
Mutations in the voltage-gated potassium channel subunit, KV8.2 (KCNV2), underlie an inherited cone-rod dystrophy. However, the role of these channels in normal photoreceptor signaling is unclear. In expression systems, KV8.2 subunits do not form functional homomeric channels, but instead combine with KV2 subunits to alter their electrical properties. KV8.2-containing heteromeric channels may mediate IKx (Beech and Barnes, 1989), a delayed-rectifer potassium current thought to counter-balance the dark current and help set the photoreceptor membrane potential. The goals of this study were to: 1) determine the protein localization and subunit interactions of retinal KV8.2 channels and 2) to characterize the IKx current in primate cones.
We used subunit-specific antibodies to localize KV8.2, KV2.1 and KV2.2 in macaque (n=12) and human retina (n=4). Co-immunoprecipitation and western blot assays were performed on macaque retinal lysates to examine KV subunit interactions. Voltage-clamp recordings were made from cone inner segments in macaque retinal wholemounts. For these recordings, the cone IKx current was isolated by recording in a Ca2+-free extracellular solution that contained 1.15 mM Co2+ and 4 mM Cs+ to block other voltage-gated conductances.
We found that KV8.2 and KV2.1 were localized to the membranes of rod and cone inner segments, whereas the Kv2.2 subunit was present only in cone inner segments. The fluorescence intensity of KV2.2 was significantly lower in S- compared with L/M- cone photoreceptors (p < 0.05, n=4 human retinae). Co-immunoprecipitation experiments revealed interactions between KV8.2 and both the KV2.1 and KV2.2 subunits (n = 3). Finally, we used voltage-clamp recordings to characterize the putative cone IKx current. IKx activated between -70 and -30 mV, with a maximum conductance of 1.16 ± 0.04 nS, half-maximal activation at -54 ± 1 mV and conductance increasing e-fold every 5.8 ± 0.3 mV (mean ± s.e.m, 11 cones from 3 retinas).
Our results suggest that the KV8.2 subunit forms heteromeric channels with KV2.1 in rods and with KV2.1 and KV2.2 in cones. These potassium channels are localized to the photoreceptor inner segment where they likely mediate the IKx current. Future studies will examine how differences in KV channel composition impact rod and cone signaling.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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