Figure 1.

General functions of Müller cells. (a, b) Müller cells maintain the homeostasis of ions and water. Water and ions are transported into Müller cells mainly through Kir2.1 and aquaporin on the Müller cell membrane, which forms synapses with retinal neurons. Then, the water and ions are transported out of the Müller cells through Kir2.1 and AQP4 on the cell membrane adjacent to the vascular plexuses and vitreous cavity. (c) Lactic acid produced from glycolysis in Müller cells can be converted to pyruvate, which can be transported out of Müller cells through the transporter monocarboxylate transporter 2 (MCT2) and then into neurons as a metabolic substrate for the tricarboxylic acid cycle (TAC). (d) Retinal neurons, such as photoreceptors, release glutamate while transmitting visual signals. Müller cells can absorb these neurotransmitters and direct them into two different metabolic pathways: glutamate can be converted into glutamine through glutamate synthetase (GS) and then released out of Müller cells through sodium-coupled neutral amino acid transporter (SNAT) and finally transported back into neurons.