Voltage-dependent Ca2+ channels, not ryanodine receptors, activate Ca2+-dependent BK potassium channels in human retinal pigment epithelial cells
| Autor: | Wimmers, Sönke, Halsband, Claire, Seyler, Sebastian, Milenkovic, Vladimir, Strauß, Olaf |
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| Jazyk: | angličtina |
| Rok vydání: | 2008 |
| Předmět: |
Protein Subunits
Calcium Channels L-Type Gene Expression Regulation Caffeine Humans Calcium Ryanodine Receptor Calcium Release Channel Large-Conductance Calcium-Activated Potassium Channels Retinal Pigment Epithelium 3-Pyridinecarboxylic acid 1 4-dihydro-2 6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)- Methyl ester Ion Channel Gating Research Article Cell Line |
| Zdroj: | Molecular Vision |
| ISSN: | 1090-0535 |
| Popis: | 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 α 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. |
| Databáze: | OpenAIRE |
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