Expression and cellular function of KCNQ channels in the eye

Abstract

KCNQ subunits (1 to 5) form voltage-gated potassium channels. They are responsible of the M-current that regulates neuronal excitability in the CNS. KCNQ4 and -5 expression has been reported in the retina where could participate in the visual processing. Our aim was to investigate the expression and function of KCNQ channels in different tissues of the eye, employing KO mice for subunits 3 to 5. By KO-controlled immunofluorescence, we found a weak labeling of KCNQ4 in retinal pigmented epithelium (RPE) cells and the ciliary body (CB). KCNQ4 signal in RPE was stronger in the area adjacent to the CB and located in the apical membrane of the cells. In the CB the signal was placed in the basal membrane of the pigmented epithelium (PE) cells. KCNQ5 was found neither in the retina nor RPE or CB. Finally, KCNQ3 was observed in non-pigmented epithelium (NPE) cells of the CB. Gene expression analysis by RT-PCR showed that all KCNQ subunits were present in RPE/retinal tissue while in CB were only KCNQ1, -4 and - 5. This profile was altered in KCNQ4 KO mouse with the appearance of KCNQ2. By patch-clamp, we observed the M-current in 40% of the RPE cells while it was absent in the KCNQ4 KO mouse. In CB, the M-current was present in NPE cells, however it could not be analyzed in PE cells. NPE cell-currents were preserved in KCNQ4 KO mouse. In conclusion, KCNQ4 may participate in the homeostasis of K+ in the subretinal space and the ciliary body, contributing to transepithelial transport.