Functional role of purinergic receptor in retinal pigment epithelial cells

Abstract

The RPE cell serves very important functions to support vision. RPE functions for vision are controlled by increase in intracellular-free Ca2+. The ATP stimulation induces the physiologic changes in the RPE. Some of the ATP can stimulate the P2 receptors on RPE cells and lead to increase intracellular Ca2+ concentrations in RPE cells. The increased intracellular Ca2+ may open Ca2+ activated K+ channel. Several previous studies of Kir 4.1 channel have reported. But the details of Kir 4.1 channel mechanism have to be completely defined. I examed Ca2+ activated K+ channel and Kir 4.1 channel in ARPE cells.I confirmed the various expression of Ca2+-activated K+ channels subunits such as small-like conductance Ca2+-activated K+ channels (SK) as well as large-like conductance in ARPE-19 cells using a combined molecular biological and electrophysiological study. The presence of Ca2+-activated K+ channel are identified by expression profile of transcripts encoding BK and SK channel subunits (i.e., BKα1, BKβ3, BK β4, SK1, SK3 and SK4/IK). The BK, IK and SK current-voltage relationship yielded a single-channel conductance of 219.6 ± 3.26 pS, 20.24 ±0.73 and 12.55 ± 0.11 pS, respectively. I treated ATP at ARPE cells. The increases of ATP-induced intracellular-free Ca2+ were found to result predominantly from release of Ca2+ from cytosolic Ca2+ stores implying that these are mediated by activation of P2Y receptors. It was found that ATP-dependent increases in intracellular free Ca2+ activate Ca2+-dependent K+ channels leading to increase open probabilities of their single channels using attached patches. ATP-induced transient increased of intracellular Ca2+ in RPE activate to BK channels and SK channels in ARPE-19 cells. SK channel was more activated than BK channel by increase of intracellular Ca2+. It is probable that SK channel is physiologically more important than BK channel for homeostasis of K+ in RPE cells. The application of ATP to RPE did not immediately effect on current density of Kir4.1 channel. Long term incubation(24 hours) of RPE with ATP decreased current density of Kir4.1 channel. Decreased current density of Kir4.1 channel occured via a mechanism that requires Gαq, subunit of G protein. There was no effects of DAG to change of the current density of Kir4.1 channel. Current density change was independent of PKC. Decreased current density of Kir4.1 channel by long term incubation of RPE with ATP occurred through a mechanism involving caveolin-mediated endocytosis of Kir4.1 channel in cell membrane. Including this study, the more investigation of ion channels in the RPE will provide further information of the physiology and pathophysiology of the RPE.