Retinal pigment epithelium (RPE) interacts with photoreceptors and supports visual function. Many of these functions such as visual cycle or secretion are regulated by increases in intracellular Ca²⁺ as second-messenger. Store operated calcium entry (SOCE) is an important mechanism in calcium signaling to regulate many cellular processes. In native RPE cells little is known about I_CRAC channel activation. We aim to show activation of SOCE through I_CRAC channel pathway in primary pig RPE cells close to in vivo conditions.

Methods: 

RT-PCR and FURA 2AM Ca²⁺ imaging in pig RPE cells 48 h after preparation.

Result: 

RT-PCR revealed expression of I_CRAC channel proteins Orai 1-3 and in addition Stim 1and 2 proteins. Activation of SOCE was induced by depletion of Ca²⁺ store (ER) in the presence or absence of thapsigargin (1mM) under extracellular Ca²⁺ free conditions. Re-adding of extracellular Ca²⁺ increased intracellular Ca²⁺ by 15 fold of basal calcium (n=9). This was blocked with 2-APB (75mM) but not with SKF (50mM). Due to the large increase of Ca²⁺ trigged by thapsigargin, 2-APB (5mM) had no effect but when the depletion was only with extracellular Ca²⁺ free, 2-APB (5mM) increased intracellular Ca²⁺ from 123 nM to 151 nM.

Conclusions: 

Short-time RPE cell culture which is close to in vivo conditions show functional presence of Orai probably regulated by Stim activation. Our findings bring a new pathway of calcium signaling in the RPE that give insight on function of endogenously expressed proteins in this tissue which are involved in Ca²⁺ signaling.