Activation of P2Y receptors stimulates potassium and cation currents in acutely isolated human Müller (glial) cells.
The ability of various neurotransmitters/neuroactive substances to induce fast, transient rises of Ca(2+)-activated K(+) currents (I(BK)) caused by release of Ca(2+) from intracellular stores was investigated in Müller glial cells of the human retina. Müller cells were enzymatically isolated from retinas of healthy donors or of patients with proliferative vitreoretinopathy, and the transmembrane ionic currents were recorded using the whole-cell and the cell-attached patch-clamp techniques. The results of the screening experiments indicate that human Müller cells express, in addition to GABA(A) and perhaps glutamatergic and cholinergic receptors, predominantly P2 receptors. ATP and other nucleotides exerted two effects on membrane currents: repetitive transient increases of the I(BK) amplitude and, in a subpopulation of cells investigated, the appearance of a transient cation conductance at negative potentials. ATP and UTP increased dose-dependently the I(BK) amplitude with half-maximal effects at 0.33 and 0.50 microM, respectively. Since several different P2 receptor agonists increased the I(BK), it is assumed that human Müller cells express a mixture of different types of P2Y receptors. In cell-attached patches, extracellular application of ATP or UTP transiently increased the open probability of single putative BK channels. The increase of I(BK) and the appearance of the cation conductance in whole-cell records were abolished when intracellular Ca(2+) was buffered by a high-EGTA pipette solution or when IP(3) was included in the pipette solution. The expression of agonist-evoked transient cation currents was found to be stronger in cells from patients as compared to cells from healthy donors. It is concluded that human Müller glial cells express P2Y receptors that, via IP(3) formation, cause intracellular Ca(2+) release. The increased intracellular Ca(2+) concentration stimulates the activity of BK channels and may induce opening of cation channels. Both the ATP-induced activity of BK channels and the increased expression of Ca(2+)-gated cation channels may be important in respect to proliferative Müller cell gliosis.
Bringmann
Andreas
A
Paul Flechsig Institute of Brain Research, Department of Neurophysiology, University of Leipzig, Leipzig, Germany. bria@server3.medizin.uni-leipzig.de
Pannicke
Thomas
T
Weick
Michael
M
Biedermann
Bernd
B
Uhlmann
Susann
S
Kohen
Leon
L
Wiedemann
Peter
P
Reichenbach
Andreas
A
D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D027682:Cation Transport Proteins / Q000187:drug effects / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009457:Neuroglia / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000819:agonists; D009711:Nucleotides / Q000494:pharmacology; D009924:Organ Culture Techniques; D010455:Peptides / Q000494:pharmacology; D010693:Phloretin / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000819:agonists / Q000378:metabolism*; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects / Q000378:metabolism; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D058472:Receptors, Purinergic P2Y1; D012160:Retina / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D014544:Uridine Triphosphate / Q000378:metabolism / Q000494:pharmacology
D015220:Calcium Channels; D027682:Cation Transport Proteins; D002614:Chelating Agents; D004791:Enzyme Inhibitors; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018377:Neurotransmitter Agents; D009711:Nucleotides; C546382:P2RY1 protein, human; D010455:Peptides; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D018160:Receptors, Cytoplasmic and Nuclear; D018048:Receptors, Purinergic P2; D058472:Receptors, Purinergic P2Y1; C064719:iberiotoxin; D000255:Adenosine Triphosphate; D010693:Phloretin; D014544:Uridine Triphosphate