Wimmers, Soenke and Halsband, Claire and Seyler, Sebastian and Milenkovic, Vladimir and Strauss, Olaf (2008) Voltage-dependent Ca2+ channels, not ryanodine receptors, activate Ca2+-dependent BK potassium channels in human retinal pigment epithelial cells. MOLECULAR VISION, 14 (269-70). pp. 2340-2348. ISSN 1090-0535,
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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 a 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.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | K+ CURRENTS; NEUROTRANSMITTER RELEASE; CALCIUM-CHANNELS; BRAIN NEURONS; ION CHANNELS; CONDUCTANCE; SUBUNITS; STIMULATION; FRESH; RPE; |
| Subjects: | 600 Technology > 610 Medical sciences Medicine |
| Divisions: | Medicine > Lehrstuhl für Augenheilkunde |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 14 Oct 2020 09:00 |
| Last Modified: | 14 Oct 2020 09:00 |
| URI: | https://pred.uni-regensburg.de/id/eprint/29929 |
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