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Upregulation of P2X(7) receptor currents in Müller glial cells during proliferative vitreoretinopathy
A Bringmann1, T Pannicke, V Moll
1Department of Neurophysiology, Paul Flechsig Institute of Brain Research, University of Leipzig, Jahnallee 59, D-04109 Liepzig, Germany. bria@server3.medizin.uni-liepzig.de
Purpose:
Müller glial cells from the human retina express purinergic P2X(7) receptors. Because extracellular adenosine triphosphate (ATP) is assumed to be a mediator of the induction or maintenance of gliosis, this study was undertaken to determine whether the expression of these receptors is different in human Müller cells obtained from retinas of healthy donors and of patients with choroidal melanoma and proliferative vitreoretinopathy (PVR).
Methods:
Human Müller cells were enzymatically isolated from donor retinas, and whole-cell patch-clamp recordings were made to characterize the density of the P2X(7) currents and the activation of currents through Ca2+-activated K+ channels of big conductance (I:(BK)) that reflects the increase of the intracellular Ca2+ concentration.
Results:
Stimulation by external ATP or by benzoylbenzoyl ATP (BzATP) evoked both release of Ca2+ from thapsigargin-sensitive intracellular stores and opening of Ca2+ -permeable P2X(7) channels. These responses caused transient and sustained increases in I:(BK). In Müller cells from patients with PVR, the mean density of the BzATP-evoked cation currents was significantly greater compared with cells from healthy donors. As a consequence, such cells displayed an enlarged I:(BK) during application of purinergic agonists. ATP and BzATP increased the DNA synthesis rate of cultured cells. This effect could be reversed by blocking the I:(BK).
Conclusions:
The increased density of P2X(7) receptor channels may permit a higher level of entry of extracellular Ca2+ into cells from patients with PVR. Enhanced Ca2+ entry and the subsequent stronger activation of I:(BK) may contribute to the induction or maintenance of proliferative activity in gliotic Müller cells during PVR.
Insights
Müller cells in proliferative vitreoretinopathy (PVR) show increased P2X(7) receptors, leading to higher calcium entry and potentially driving gliosis. This suggests P2X(7) receptors are key in PVR progression.
Area of Science:
- Neuroscience
- Ophthalmology
- Cell Biology
Background:
- Müller glial cells are crucial retinal support cells.
- Purinergic receptors, particularly P2X(7), are implicated in cellular responses to injury.
- Extracellular adenosine triphosphate (ATP) may mediate gliosis, a reactive cell proliferation.
Purpose of the Study:
- To investigate differences in P2X(7) receptor expression in human Müller cells from healthy donors versus patients with choroidal melanoma and proliferative vitreoretinopathy (PVR).
- To explore the functional consequences of altered P2X(7) receptor expression on Müller cell activity.
Main Methods:
- Enzymatic isolation of human Müller cells from donor and patient retinas.
- Whole-cell patch-clamp recordings to measure P2X(7) currents and Ca2+-activated K+ channels (I:(BK)).
- Assessment of intracellular calcium concentration changes and DNA synthesis rates.
Main Results:
- ATP and benzoylbenzoyl ATP (BzATP) stimulated Ca2+ release and P2X(7) channel opening in Müller cells.
- Müller cells from PVR patients exhibited significantly higher BzATP-evoked cation currents compared to healthy controls.
- Purinergic agonist stimulation increased DNA synthesis, an effect reversible by blocking I:(BK).
Conclusions:
- Increased P2X(7) receptor density in PVR Müller cells allows greater extracellular Ca2+ influx.
- Enhanced Ca2+ entry and subsequent I:(BK) activation may contribute to the proliferative activity of gliotic Müller cells in PVR.
- P2X(7) receptors represent a potential therapeutic target for managing PVR.
