Differential effects of endothelin-1 on calcium mobility in cultured porcine pigment epithelial cells of iris and retina.
OBJECTIVE
Photoreceptor function depends on an intact retina pigment epithelial (RPE) cell layer. Transplantation of iris pigment epithelial (IPE) cells to the subretinal space offers a potential alternative to RPE transplantation in patients with severe retinal diseases such as macular degeneration. Whether the functions of IPE and RPE are similar or different is not well established. The purpose of this study was to identify the characteristics of IPE cells and RPE cells by detecting the effects of endothelin-1 (ET-1) on intracellular free Ca(2+) ([Ca(2+)](i)) mobility in these cells.


METHODS
Iris and retina pigment epithelial cells were cultured from porcine eyeballs. After the cells were loaded with fura-2/AM, fluorescence was monitored with a fluorescent spectrophotometer by continuously recording excitation signals at 340 nm and 380 nm and emission signals at 510 nm.


RESULTS
IPE and RPE cells induced a significant increase in [Ca(2+)](i) under exposure to 10(-7), 10(-8), and 10(-9) mol/L ET-1 in Ca(2+)-containing buffer. In the presence of Ca(2+)-free buffer, ET-1 alone induced an increase in [Ca(2+)](i) in iris but not in retina pigment epithelial cells. In Ca(2+)-free buffer, pretreatment of the IPE cells with 10(-7) mol/L ET-1 partially inhibited thapsigargin-induced [Ca(2+)](i) increase and carbonylcyanide m-chlorophenylhydrazone (CCCP)-induced Ca(2+) release. Similarly, pretreatment of the IPE cells with thapsigargin or CCCP also partially inhibited ET-1-induced [Ca(2+)](i) increase. The [Ca(2+)](i) release induced by 10(-7) mol/L ET-1 was not inhibited by the phospholipase C inhibitor U73122. In Ca(2+)-containing buffer, the ET(A) receptor antagonist BQ123 and ET(B) receptor antagonist BQ788 partially inhibited 10(-7) mol/L ET-1-induced [Ca(2+)](i) increase in IPE cells. However, BQ123 partially inhibited the 10(-7) mol/L ET-1-induced [Ca(2+)](i) increase in RPE cells. Nifedipine partially inhibited 10(-7) mol/L ET-1-induced [Ca(2+)](i) increase in both types of pigment cells.


CONCLUSIONS
These results suggest that iris and retina pigment epithelial cells possess distinguishing characteristics because the ET-1-induced [Ca(2+)](i) increases in these 2 types of pigment epithelial cells are regulated by distinct mechanisms.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D019332:Endothelin-1 / Q000494:pharmacology*; D007498:Iris / Q000166:cytology / Q000378:metabolism*; D012160:Retina / Q000166:cytology / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013552:Swine
D019332:Endothelin-1; D002118:Calcium