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http://purl.uniprot.org/citations/19096717http://www.w3.org/1999/02/22-rdf-syntax-ns#typehttp://purl.uniprot.org/core/Journal_Citation
http://purl.uniprot.org/citations/19096717http://www.w3.org/2000/01/rdf-schema#comment"

Purpose

In different tissues the activation of large conductance Ca2+-activated (BK) potassium channels has been shown to be coupled to voltage-gated Ca2+ channels as well as ryanodine receptors. As activation of BK channels leads to hyperpolarization of the cell, these channels provide a negative feedback mechanism for Ca2+-induced functions. Many cellular functions of the retinal pigment epithelium (RPE) are coupled to changes in [Ca2+]i. The aim of this study was to identify which Ca2+-entry pathway leads to the activation of BK channels in the RPE.

Methods

We used freshly isolated human RPE cells and the ARPE-19 cell line for the detection of transcripts of BK channel alpha subunits. Patch-Clamp measurements were used to characterize BK channels in ARPE-19 cells electrophysiologically. To monitor changes in [Ca2+]i ARPE-19 cells were loaded with Fura-2.

Results

Freshly isolated human RPE cells and ARPE-19 cells were shown to express BK channels. In ARPE-19 cells these channels were shown to be functionally active. Application of iberiotoxin led to a block of outward currents by 28.15%. At +50 mV ARPE-19 cells had a BK channel-mediated current density of 2.42 pA/pF. Activation of ryanodine receptors by caffeine led to a significant increase in [Ca2+]i by 34.16%. Nevertheless, caffeine-induced Ca2+ signals were not sufficient to activate BK channels. Instead, the activation of L-type Ca2+ channels by BayK 8644 caused a dramatic increase in BK channel activity and a shift of the reversal potential of the ARPE-19 cells by -22.6 mV.

Conclusions

We have shown here for the first time that human RPE cells express BK channels. These channels are activated in RPE cells by increases in [Ca2+]i that are mediated by the opening of voltage gated L-type Ca2+ channels. As Ca2+ entering the RPE cells through these Ca2+ channels are known to be important for growth factor secretion and light-induced transepithelial transport, we speculate that BK channels coupled directly to these Ca2+ channels may provide a good tool for negative feedback control of the L-type Ca2+ channels."xsd:string
http://purl.uniprot.org/citations/19096717http://purl.uniprot.org/core/author"Wimmers S."xsd:string
http://purl.uniprot.org/citations/19096717http://purl.uniprot.org/core/author"Strauss O."xsd:string
http://purl.uniprot.org/citations/19096717http://purl.uniprot.org/core/author"Halsband C."xsd:string
http://purl.uniprot.org/citations/19096717http://purl.uniprot.org/core/author"Milenkovic V."xsd:string
http://purl.uniprot.org/citations/19096717http://purl.uniprot.org/core/author"Seyler S."xsd:string
http://purl.uniprot.org/citations/19096717http://purl.uniprot.org/core/date"2008"xsd:gYear
http://purl.uniprot.org/citations/19096717http://purl.uniprot.org/core/name"Mol Vis"xsd:string
http://purl.uniprot.org/citations/19096717http://purl.uniprot.org/core/pages"2340-2348"xsd:string
http://purl.uniprot.org/citations/19096717http://purl.uniprot.org/core/title"Voltage-dependent Ca2+ channels, not ryanodine receptors, activate Ca2+-dependent BK potassium channels in human retinal pigment epithelial cells."xsd:string
http://purl.uniprot.org/citations/19096717http://purl.uniprot.org/core/volume"14"xsd:string
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