KCNQ5/K(v)7.5 potassium channel expression and subcellular localization in primate retinal pigment epithelium and neural retina.
ABSTRACT Previous studies identified in retinal pigment epithelial (RPE) cells an M-type K(+) current, which in many other cell types is mediated by channels encoded by KCNQ genes. The aim of this study was to assess the expression of KCNQ genes in the monkey RPE and neural retina. Application of the specific KCNQ channel blocker XE991 eliminated the M-type current in freshly isolated monkey RPE cells, indicating that KCNQ subunits contribute to the underlying channels. RT-PCR analysis revealed the expression of KCNQ1, KCNQ4, and KCNQ5 transcripts in the RPE and all five KCNQ transcripts in the neural retina. At the protein level, KCNQ5 was detected in the RPE, whereas both KCNQ4 and KCNQ5 were found in neural retina. In situ hybridization in frozen monkey retinal sections revealed KCNQ5 gene expression in the ganglion cell layer and the inner and outer nuclear layers of the neural retina, but results in the RPE were inconclusive due to the presence of melanin. Immunohistochemistry revealed KCNQ5 in the inner and outer plexiform layers, in cone and rod photoreceptor inner segments, and near the basal membrane of the RPE. The data suggest that KCNQ5 channels contribute to the RPE basal membrane K(+) conductance and, thus, likely play an important role in active K(+) absorption. The distribution of KCNQ5 in neural retina suggests that these channels may function in the shaping of the photoresponses of cone and rod photoreceptors and the processing of visual information by retinal neurons.
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ABSTRACT: Hypoxia causes vasodilatation of coronary arteries, but the underlying mechanisms are poorly understood. We hypothesized that hypoxia reduces intracellular Ca(2+) concentration ([Ca(2+) ]i ) by opening of K channels and release of H2 S. Porcine coronary arteries without endothelium were mounted for measurement of isometric tension and [Ca(2+) ]i , and the expression of voltage-gated K channels (KV ) subtype 7 (KV 7 channels encoded by KCNQ genes) and large-conductance calcium-activated K channels (BKCa ) was examined. Voltage clamp assessed the role of KV 7 channels in hypoxia. Gradual reduction of oxygen concentration from 95% to 1% dilated the coronary arteries and was associated with reduced [Ca(2+) ]i in prostaglandin F2α (PGF2α 10 μM)-contracted arteries whereas no fall in [Ca(2+) ]i was observed in 30 mM K-contracted arteries. Blockers of ATP-sensitive and voltage-gated potassium channels, and BKCa inhibited hypoxia-induced dilatation in PGF2α -contracted arteries; the inhibition was most pronounced in the presence of the Kv7 channel blockers, XE991 and linopirdine, while a KV 7.1 blocker, failed to change hypoxic vasodilatation. XE991 also inhibited H2 S- and adenosine-induced vasodilatation. PCR revealed expression of KV 7.1, KV 7.4, KV 7.5, and BKCa channels, and BKCa , KV 7.4 and KV 7.5 was also found by immunoblotting. Voltage clamp studies showed a more pronounced XE991-sensitive current in hypoxic conditions. The KV 7.4 and KV 7.5 channels, which we identified in the coronary arteries, appear to be a main component in the hypoxia-induced vasodilatation. Voltage clamp results further support a role for KV 7 channels during hypoxia. H2 S and adenosine may also lead to the activation of KV 7 channels.British Journal of Pharmacology 09/2013; · 5.07 Impact Factor
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ABSTRACT: The function of sensory hair cells of the cochlea and vestibular organs depends on an influx of K+ through apical mechanosensitive ion channels and its subsequent removal over their basolateral membrane. The KCNQ4 (Kv7.4) K+ channel, which is mutated in DFNA2 human hearing loss, is expressed in the basal membrane of cochlear outer hair cells (OHCs) where it may mediate K+ efflux. Like the related K+ channel KCNQ5 (Kv7.5), KCNQ4 is also found at calyx terminals ensheathing type I vestibular hair cells where it may be localized pre- or postsynaptically. Making use of Kcnq4-/- mice lacking KCNQ4, as well as Kcnq4dn/dn and Kcnq5dn/dn mice expressing dominant negative channel mutants, we now show unambiguously that in adult mice both channels reside in postsynaptic calyx-forming neurons, but cannot be detected in the innervated hair cells. Accordingly whole-cell currents of vestibular hair cells did not differ between genotypes. Neither Kcnq4-/-, Kcnq5dn/dn nor Kcnq4-/-/Kcnq5dn/dn double mutant mice displayed circling behavior found with severe vestibular impairment. However, a milder form of vestibular dysfunction was apparent from altered vestibulo-ocular reflexes in Kcnq4-/-/Kcnq5dn/dn and Kcnq4-/- mice. The larger impact of KCNQ4 may result from its preferential expression in central zones of maculae and cristae, which are innervated by phasic neurons that are more sensitive than the tonic neurons predominantly present in the surrounding peripheral zones where KCNQ5 is found. The impact of postsynaptic KCNQ4 on vestibular function may be related to K+ removal and modulation of synaptic transmission.Journal of Biological Chemistry 02/2013; · 4.65 Impact Factor
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ABSTRACT: Refractive error is the most common eye disorder worldwide and is a prominent cause of blindness. Myopia affects over 30% of Western populations and up to 80% of Asians. The CREAM consortium conducted genome-wide meta-analyses, including 37,382 individuals from 27 studies of European ancestry and 8,376 from 5 Asian cohorts. We identified 16 new loci for refractive error in individuals of European ancestry, of which 8 were shared with Asians. Combined analysis identified 8 additional associated loci. The new loci include candidate genes with functions in neurotransmission (GRIA4), ion transport (KCNQ5), retinoic acid metabolism (RDH5), extracellular matrix remodeling (LAMA2 and BMP2) and eye development (SIX6 and PRSS56). We also confirmed previously reported associations with GJD2 and RASGRF1. Risk score analysis using associated SNPs showed a tenfold increased risk of myopia for individuals carrying the highest genetic load. Our results, based on a large meta-analysis across independent multiancestry studies, considerably advance understanding of the mechanisms involved in refractive error and myopia.Nature Genetics 02/2013; · 35.21 Impact Factor