Upregulation of P2X(7) receptor currents in Müller glial cells during proliferative vitreoretinopathy.
OBJECTIVE
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.
Bringmann
A
A
Department of Neurophysiology, Paul Flechsig Institute of Brain Research, University of Leipzig, Jahnallee 59, D-04109 Liepzig, Germany. bria@server3.medizin.uni-liepzig.de
Pannicke
T
T
Moll
V
V
Milenkovic
I
I
Faude
F
F
Enzmann
V
V
Wolf
S
S
Reichenbach
A
A
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D018929:Cell Culture Techniques; D002830:Choroid Neoplasms / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis; D004261:DNA Replication; D004594:Electrophysiology; D005911:Gliosis / Q000378:metabolism*; D006801:Humans; D008545:Melanoma / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D009457:Neuroglia / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D058486:Receptors, Purinergic P2X7; D012160:Retina / Q000187:drug effects / Q000378:metabolism*; D015854:Up-Regulation; D018630:Vitreoretinopathy, Proliferative / Q000378:metabolism*
C546468:P2RX7 protein, human; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7; C033901:3'-O-(4-benzoyl)benzoyladenosine 5'-triphosphate; D000255:Adenosine Triphosphate; D004247:DNA