Abstract
The vitreousness of glaucoma subjects contains elevated glutamate, and excessive extracellular glutamate is toxic to retinal neurons. Therefore, glutamate clearance is potentially impaired in the retina of glaucoma subjects. Müller cells play an important role in maintaining low extracellular levels of neurotransmitters, such as glutamate. A better understanding of the cross-talk between adenosine and glutamate may provide a better characterization of the regulatory network in Müller cells. Here, Müller cells were purified from the rat retina on postnatal day 5 using the papain digestion method. Application of increasing concentrations of glutamate (0-20 mmol/L) caused a dose-dependent decrease in the expression levels of Kir4.1, Kir2.1, GLAST, and GS. Exogenous adenosine regulated Kir channels and subsequently promoted GLAST and GS expression levels in Müller cells under exogenous glutamate stimulation. These effects were partly dependent on adenosine receptors.
Highlights
Muller cells, the major glial cells in the retina, radially span the entire retina and are closely associated with all retinal cells [1]
Released glutamate in the extracellular space is primarily transported into Muller cells by L-glutamate/L-aspartate transporter (GLAST) and subsequently quickly converted to glutamine by glutamine synthetase (GS)
Muller cells were almost purified after 4-6 passages in cell cultures
Summary
The major glial cells in the retina, radially span the entire retina and are closely associated with all retinal cells [1]. The actions of adenosine are usually mediated through its interaction with specific receptor subtypes, A1, A2A, A2B, and A3 [15] All these adenosine receptors have been identified in the retina [16, 17] and are expressed in Muller cells [18]. Adenosine plays a protective role in the pathophysiology of several retinal diseases, such as diabetic retinopathy [19] and glaucoma [20] These favorable effects have been explored in vitro, and various signaling pathways have been implicated. How adenosine influences the expression levels of Kir channels in cultured Muller cells under exogenous glutamate stimulation is relatively unknown. We attempt to investigate whether adenosine can regulate Kir channels and subsequently promote the expression levels of GLAST and GS in Muller cells under exogenous glutamate stimulation
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