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Depolarization and glutamate regulate extracellular alkalization of retinal horizontal cells
The retina is a very thin layer of cells in the back of the eyeballs of vertebrates and some cephalopods. It converts light into a neural signal, and the synaptic terminals of photoreceptors connect horizontal and bipolar cells. The release of the neurotransmitter glutamate (Glu) may regulate the process of photoreception, and the mechanism of this process has been debated.
Scientists from Wesleyan University and MBL used the squid retinal horizontal cells as experimental materials to measure the proton (H + ) flow rate under various material stimuli using non-invasive micro-measurement techniques . The study found that the neurotransmitter Glu induced alkalization of the outer surface of the cell membrane, and the magnitude of the effect of Glu was related to extracellular buffer. The effects of the AMPA / kainate receptor-activated kainate and NMDA receptor-activated D-methyl-aspartate are similar to those of Glu. The proton flow rate affected by Kainate was inhibited by the AMPA / kainite receptor inhibitor CNQX, which was terminated by the NMDA receptor antagonist DAP-5. The activation of pro-metabolic glutamate receptors does not affect the proton flow rate. Increasing extracellular K + or depolarization caused by applying a negative voltage directly through a voltage clamp can lead to alkalization of the cell membrane surface. The proton flow rate caused by depolarization can be inhibited by the L-type Ca 2+ channel inhibitor 10 μm nifedipine, and the plasma membrane Ca 2+ /H + ATPase (PMCA) inhibitor carboxyeosin can also significantly reduce Glu-regulated H + changes.
The results of this study are consistent with the hypothesis of Glu-induced extracellular alkalization, which is derived from the process by which Ca 2+ enters cells caused by PMCA pump activation . This process may relieve the pressure of photoreceptor neurotransmitter release due to proton release from the exocytosis of the photoreceptor synaptic terminals. Therefore, reducing the release of H + by inhibiting Ca 2+ channels is one way to study neurotransmitters in the future.
Keywords: glutamate, depolarization, proton, retina, horizontal cells, squid
References: Matthew A. Kreitzer , et al . The Journal of General Physiology, 2007, 130: 169 - 182.
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