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Pflugers Arch. 2015 Oct;467(10):2179-91. doi: 10.1007/s00424-014-1656-2. Epub 2014 Nov 27.

Activation of endogenously expressed ion channels by active complement in the retinal pigment epithelium.

Author information

1
Max-Planck Institute of Psychiatry, Munich, Germany.
2
Experimental Ophthalmology, Eye Clinic, University Medical Center Regensburg, Regensburg, Germany.
3
Experimental Ophthalmology, Department of Ophthalmology, Charite University Medicine Berlin, Campus Virchow-Klinikum, Augustenburger Platz 1, 13353, Berlin, Germany.
4
Department of Infection Biology, Leibniz Institute for Natural Product Research and Infection Biology, Jena, Germany.
5
Friedrich Schiller University, Jena, Germany.
6
Department of Ophthalmology, Medical University of South Carolina, Charleston, SC, 29425, USA.
7
Research Service, Ralph H. Johnson VA Medical Center, Charleston, SC, 29401, USA.
8
Experimental Ophthalmology, Eye Clinic, University Medical Center Regensburg, Regensburg, Germany. olaf.strauss@charite.de.
9
Experimental Ophthalmology, Department of Ophthalmology, Charite University Medicine Berlin, Campus Virchow-Klinikum, Augustenburger Platz 1, 13353, Berlin, Germany. olaf.strauss@charite.de.

Abstract

Defective regulation of the alternative pathway of the complement system is believed to contribute to damage of retinal pigment epithelial (RPE) cells in age-related macular degeneration. Thus we investigated the effect of complement activation on the RPE cell membrane by analyzing changes in membrane conductance via patch-clamp techniques and Ca(2+) imaging. Exposure of human ARPE-19 cells to complement-sufficient normal human serum (NHS) (25 %) resulted in a biphasic increase in intracellular free Ca(2+) ([Ca(2+)]i); an initial peak followed by sustained Ca(2+) increase. C5- or C7-depleted sera did not fully reproduce the signal generated by NHS. The initial peak of the Ca(2+) response was reduced by sarcoplasmic Ca(2+)-ATPase inhibitor thapsigargin, L-type channel blockers (R)-(+)-BayK8644 and isradipine, transient-receptor-potential (TRP) channel blocker ruthenium-red and ryanodine receptor blocker dantrolene. The sustained phase was carried by CaV1.3 L-type channels via tyrosine-phosphorylation. Changes in [Ca(2+)]I were accompanied by an abrupt hyperpolarization, resulting from a transient increase in membrane conductance, which was absent under extracellular Ca(2+)- or K(+)-free conditions and blocked by (R)-(+)-BayK8644 or paxilline, a maxiK channel inhibitor. Single-channel recordings confirmed the contribution of maxiK channels. Primary porcine RPE cells responded to NHS in a comparable manner. Pre-incubation with NHS reduced H2O2-induced cell death. In summary, in a concerted manner, C3a, C5a and sC5b-9 increased [Ca(2+)]i by ryanodine-receptor-dependent activation of L-type channels in addition to maxi-K channels and TRP channels absent from any insertion of a lytic pore.

KEYWORDS:

(4–6): complement system; BK channels; L-type channels; RPE; Retinal pigment epithelium

PMID:
25427445
DOI:
10.1007/s00424-014-1656-2
[Indexed for MEDLINE]

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