Abstract
In response to light, most retinal neurons exhibit gradual changes in membrane potential. Therefore K+ channels that mediate threshold currents are well-suited for the fine-tuning of signal transduction. In the present study we demonstrate the expression of the different Kv11 (ether-à-go-go related gene; erg) channel subunits in the human and mouse retina by RT PCR and quantitative PCR, respectively. Immunofluorescence analysis with cryosections of mouse retinae revealed the following local distribution of the three Kv11 subunits: Kv11.1 (m-erg1) displayed the most abundant expression with the strongest immunoreactivity in rod bipolar cells. In addition, immunoreactivity was found in the inner part of the outer plexiform layer (OPL), in the inner plexiform layer (IPL) and in the inner segments of photoreceptors. Immunoreactivity for Kv11.2 (m-erg2) was observed in the outer part of the OPL and throughout the IPL. Double-labeling for vGluT1 or synaptophysin indicated a mainly presynaptic localization of Kv11.2. While no significant staining for Kv11.3 (m-erg3) was detected in the neuronal retina, strong Kv11.3 immunoreactivity was present in the apical membrane of the retinal pigment epithelium. The different expression levels were confirmed by real-time PCR showing almost equal levels of Kv11.1 and Kv11.2, while Kv11.3 mRNA expression was significantly lower. The two main splice variants of Kv11.1, isoforms a and b were detected in comparable levels suggesting a possible formation of cGMP/cGK-sensitive Kv11.1 channels in photoreceptors and rod bipolar cells. Taken together, the immunohistological results revealed different expression patterns of the three Kv11 channels in the mouse retina supposing distinct physiological roles.
Highlights
The vertebrate retina is a neuronal network which consists of six major cell types
RT PCR experiments We investigated the mRNA expression of all three Kv11 channel subunits in mouse and human retinas by RT PCR
While Kv11.1 subunits displayed a relatively wide-spread distribution in different retinal layers, Kv11.2 subunit expression was detected predominantly presynaptically in the glutamatergic photoreceptors and bipolar cells, and Kv11.3 immunoreactivity was detected in the apical membrane of the retina supporting cell layer of the retinal pigment epithelium (RPE) and in choroidal and retinal blood vessels
Summary
The vertebrate retina is a neuronal network which consists of six major cell types. The incoming light is detected by photoreceptors and the information is subsequently passed through bipolar cells to ganglion cells which form the optic nerve. In contrast to some subtypes of amacrine cells and the ganglion cells which are able to generate action potentials, neurotransmitter release from most retinal neurons is triggered by only gradual changes of the membrane potential. Kv11 (ether a-go-go related gene; erg) K+ channels belong to the EAG family of voltage-gated K+ channels. Most members of this family (Kv10 or eag, Kv11 or erg, and Kv12 or elk channels) share an activation threshold at relatively negative potentials [4]. These channels are able to control the membrane potential in retinal neurons in their rested and activated state.
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