May 2004
Volume 45, Issue 13
Free
ARVO Annual Meeting Abstract  |   May 2004
Cloning and molecular characterization of L type Ca2+ channels in the retinal pigment epithelium
Author Affiliations & Notes
  • S. Wimmers
    Experimentelle Ophthalmologie, Universitatsklinikum Hamburg, Hamburg, Germany
  • L. Coeppicus
    Experimentelle Ophthalmologie, Universitatsklinikum Hamburg, Hamburg, Germany
  • O. Strauss
    Experimentelle Ophthalmologie, Universitatsklinikum Hamburg, Hamburg, Germany
  • Footnotes
    Commercial Relationships  S. Wimmers, None; L. Coeppicus, None; O. Strauss, None.
  • Footnotes
    Support  DFG STR480/8–2
Investigative Ophthalmology & Visual Science May 2004, Vol.45, 3688. doi:
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      S. Wimmers, L. Coeppicus, O. Strauss; Cloning and molecular characterization of L type Ca2+ channels in the retinal pigment epithelium . Invest. Ophthalmol. Vis. Sci. 2004;45(13):3688.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Abstract: : Purpose: Secretion of various growth factors by the retinal pigment epithelium (RPE) is substantial for normal structure of the retina but also plays a role in the etiology of retinal diseases. Further, the RPE itself is the target of cytokines. L type channels are mediating intracellular processing from incoming signals and subsequent growth factor secretion.To resolve the molecular structure function relation of the Ca2+ channels expressed by the RPE because of its importance in the regulation of cytokine secretion and its possible role in the formation of chorioidal neovascularization (CNV). Methods:The biophysical properties of Ca2+ currents in the RPE were investigated by the patch–clamp technique. The complete coding sequence of the pore forming α subunit of the human RPE cell line ARPE–19 and from patients with CNV was cloned and the expression pattern of accessory subunits (ß and α2δ) was investigated by RT–PCR. Results: The RPE from patients with CNV have Ba2+ currents that were reduced by nifedipine (to 69.8% with 10 µM; n=6) and stimulated by high concentrations of BayK 8644 (to 147% with 5 µM; n=4) but insensitive to low concentrations of BayK 8644 (97.6% with 0.5 µM; n=9). The currents displayed very fast inactivation kinetics (τinact = 4.0 ± 1.1 ms). We found the pore forming α subunit Cav1.3 to be expressed in a not yet described splicing variant lacking exons 8, 11, 32 and 44 in CNV cells and exons 11, 32 and 44 in ARPE–19 cells. The expression pattern of the accessory Ca2+ channel subunits showed some differences between the cell line and the primary culture as well (e.g. α2δ3 is expressed in our primary culture but not in ARPE–19–cells whereas with ß2 it is the other way around). Discussion: The Ba2+ currents we found in RPE cells had dihydropyridine sensitivities like neuroendocrine Ca2+ channels. Consistently, we found the Cav1.3 α subunit to be expressed in the RPE. The obvious differences in the inactivation kinetics between neuroendocrine Ca2+ channels in the RPE and other cells may be explained an yet unknown regulation mechanism of the channels in the RPE. These differences may be caused by the expression of the splicing variant and the expression pattern of accessory subunits.

Keywords: ion channels • retinal pigment epithelium • age–related macular degeneration 
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