title: Activation of endogenously expressed ion channels by active complement in the retinal pigment epithelium.
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.
authors.affiliation: Max-Planck Institute of Psychiatry, Munich, Germany.|Experimental Ophthalmology, Eye Clinic, University Medical Center Regensburg, Regensburg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Genewsky
authors.affiliation: Experimental Ophthalmology, Eye Clinic, University Medical Center Regensburg, Regensburg, Germany.
authors.forename: Ingmar
authors.initials: I
authors.lastname: Jost
authors.affiliation: Experimental Ophthalmology, Department of Ophthalmology, Charite University Medicine Berlin, Campus Virchow-Klinikum, Augustenburger Platz 1, 13353, Berlin, Germany.
authors.forename: Catharina
authors.initials: C
authors.lastname: Busch
authors.affiliation: Experimental Ophthalmology, Department of Ophthalmology, Charite University Medicine Berlin, Campus Virchow-Klinikum, Augustenburger Platz 1, 13353, Berlin, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Huber
authors.affiliation: Experimental Ophthalmology, Eye Clinic, University Medical Center Regensburg, Regensburg, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Stindl
authors.affiliation: Department of Infection Biology, Leibniz Institute for Natural Product Research and Infection Biology, Jena, Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Skerka
authors.affiliation: Department of Infection Biology, Leibniz Institute for Natural Product Research and Infection Biology, Jena, Germany.|Friedrich Schiller University, Jena, Germany.
authors.forename: Peter F
authors.initials: PF
authors.lastname: Zipfel
authors.affiliation: Department of Ophthalmology, Medical University of South Carolina, Charleston, SC, 29425, USA.|Research Service, Ralph H. Johnson VA Medical Center, Charleston, SC, 29401, USA.
authors.forename: Bärbel
authors.initials: B
authors.lastname: Rohrer
authors.affiliation: Experimental Ophthalmology, Eye Clinic, University Medical Center Regensburg, Regensburg, Germany. olaf.strauss@charite.de.|Experimental Ophthalmology, Department of Ophthalmology, Charite University Medicine Berlin, Campus Virchow-Klinikum, Augustenburger Platz 1, 13353, Berlin, Germany. olaf.strauss@charite.de.
authors.forename: Olaf
authors.initials: O
authors.lastname: Strauß
mesh_terms: D000200:Action Potentials; D000818:Animals; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D020013:Calcium Signaling; D002460:Cell Line; D002478:Cells, Cultured; D003165:Complement System Proteins / Q000494:pharmacology*; D006801:Humans; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D013552:Swine
chemical_list: D020746:Calcium Channels, L-Type; D051036:Large-Conductance Calcium-Activated Potassium Channels; D019837:Ryanodine Receptor Calcium Release Channel; D003165:Complement System Proteins
keywords: (4–6): complement system; BK channels; L-type channels; RPE; Retinal pigment epithelium