Expression profile of voltage-dependent Ca2+ channel subunits in the human retinal pigment epithelium.
BACKGROUND
The secretion of a variety of factors by the retinal pigment epithelium (RPE) is essential for the structural integrity of the neuronal retina and choroid, but also plays a pivotal role in the etiology of diseases such as choroidal neovascularisation. A recent study showed that the secretory activity of the RPE is regulated by the activity of a certain type of voltage-dependent Ca(2+) channels, the L-type channel. In order to provide a better base for the understanding of the underlying Ca(2+) signalling in these cells, we investigated the expression profile of voltage-dependent Ca(2+) channel subunits in RPE cells.


METHODS
Using RT-PCR techniques with cDNA isolated from RPE cells, we investigated the expression pattern of Ca(2+) channel subunits. Furthermore, we analysed Ba(2+) currents through voltage-dependent Ca(2+) channels in RPE cells by the patch-clamp technique.


RESULTS
We detected the expression of two L-type channel subtypes and the expression of two different T-type channel subtypes. As accessory subunits, they expressed beta2 and beta4 and all known alpha(2)delta subunits. In general, we were able to confirm these data with cDNA from the ARPE-19 cell line. They only showed some differences in their expression pattern of accessory subunits. Since the expression of T-type channels was so far unknown in RPE cells, we confirmed their expression in the RPE using cDNA isolated from freshly isolated human RPE cells. Furthermore, the patch-clamp analysis of Ba(2+) currents showed a heterogeneous pattern of voltage-dependent inward currents in RPE cells. In some cells, typical slowly inactivating L-type currents were detected, whereas in other cells fast inactivating T-type currents could be detected.


CONCLUSIONS
These data indicate the expression of a so far not detected subtype of voltage-dependent Ca(2+) channels, the T-type channels. Together with the expression of L-type channels, RPE cells show a comparable expression pattern to that of other secretory cells, such as beta-islets of the pancreas.
Wimmers
Sönke
S
Experimentelle Ophthalmologie, Klinik und Poliklinik für Augenheilkunde, Universitätsklinikum Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany. wimmers@uke.uni-hamburg.de
Coeppicus
Linn
L
Rosenthal
Rita
R
Strauss
Olaf
O
D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000235:genetics*; D020013:Calcium Signaling / Q000502:physiology; D002460:Cell Line; D015870:Gene Expression / Q000502:physiology*; D020869:Gene Expression Profiling; D006801:Humans; D018408:Patch-Clamp Techniques; D010857:Pigment Epithelium of Eye / Q000378:metabolism*; D021122:Protein Subunits / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D015220:Calcium Channels; D021122:Protein Subunits; D012333:RNA, Messenger; D002118:Calcium