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.
- SourceAvailable from: Olaf Strauss[Show abstract] [Hide abstract]
ABSTRACT: Ion channels and ion transporters play essential roles in the function of the retinal pigment epithelium (RPE). The use of cell cultures has been exploited as a key method for successfully identifying and studying ion channels and transporters of the RPE. Cultured RPE cells enable robust and long-lasting patch-clamp recordings, Ussing chamber investigations of the transepithelial transport within the isolated RPE, and analyses of the intracellular Ca2+ or pH with fluorescent probes. Furthermore, cultured RPE can be transfected at high success rates, permitting the easy use of siRNA to study the involvement of ion channels on the molecular level. However, the expression patterns of the ion channels in the RPE appear to be a very sensitive marker reflecting the extent of RPE differentiation in vitro. Having originated from the neuroectoderm, cultured RPE cells seem to retain some capacity to change into a more neuronal phenotype expressing TTX-blockable Na+ channels or synaptic Ca2+ channels. Therefore, the identification of ion channels and transporters in cultured cells should be verified in freshly isolated RPE cells and in situ preparations of the RPE, via immunohistochemistry and the analysis of RPE-specific signals in the electroretinogram from transgenic animals.Experimental Eye Research 09/2014; 126:27–37. DOI:10.1016/j.exer.2014.05.005 · 3.02 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Recently, we demonstrated the expression of KCNQ1, KCNQ4, and KCNQ5 transcripts in monkey retinal pigment epithelium (RPE) and showed that the M-type current in RPE cells is blocked by the specific KCNQ channel blocker XE991. Using patch-clamp electrophysiology, we investigated the pharmacological sensitivity of the M-type current in isolated monkey RPE cells to elucidate the subunit composition of the channel. Most RPE cells exhibited an M-type current with a voltage for half-maximal activation of approximately -35 mV. The M-type current activation followed a double-exponential time course and was essentially complete within 1 s. The M-type current was inhibited by micromolar concentrations of the nonselective KCNQ channel blockers linopirdine and XE991 but was relatively insensitive to block by 10 μM chromanol 293B or 135 mM tetraethylammonium (TEA), two KCNQ1 channel blockers. The M-type current was activated by 1) 10 μM retigabine, an opener of all KCNQ channels except KCNQ1, 2) 10 μM zinc pyrithione, which augments all KCNQ channels except KCNQ3, and 3) 50 μM N-ethylmaleimide, which activates KCNQ2, KCNQ4, and KCNQ5, but not KCNQ1 or KCNQ3, channels. Application of cAMP, which activates KCNQ1 and KCNQ4 channels, had no significant effect on the M-type current. Finally, diclofenac, which activates KCNQ2/3 and KCNQ4 channels but inhibits KCNQ5 channels, inhibited the M-type current in the majority of RPE cells but activated it in others. The results indicate that the M-type current in monkey RPE is likely mediated by channels encoded by KCNQ4 and KCNQ5 subunits.AJP Cell Physiology 11/2011; 302(5):C821-33. DOI:10.1152/ajpcell.00269.2011 · 3.67 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Photoreceptors are exquisitely adapted to transform light stimuli into electrical signals that modulate neurotransmitter release. These cells are organized into several compartments including the unique outer segment (OS). Its whole function is to absorb light and transduce this signal into a change of membrane potential. Another compartment is the inner segment where much of metabolism and regulation of membrane potential takes place and that connects the OS and synapse. The synapse is the compartment where changes in membrane potentials are relayed to other neurons in the retina via release of neurotransmitter. The composition of the plasma membrane surrounding these compartments varies to accommodate their specific functions. In this chapter, we discuss the organization of the plasma membrane emphasizing the protein composition of each region as it relates to visual signaling. We also point out examples where mutations in these proteins cause visual impairment.Current Topics in Membranes 01/2013; 72C:231-265. DOI:10.1016/B978-0-12-417027-8.00007-6 · 1.77 Impact Factor