The Effect of Histamine on Inward and Outward Currentsin Mouse Retinal Amacrine Cells

Abstract The expression of H1 receptor has been reportedin amacrine cells of mouse and rat retinae. However, weassumed that other types of histamine receptors alsofunction in amacrine cells. In order to confirm that histaminemodulates the membrane potential in mouse amacrinecells, we measured voltage-gated currents usingwhole-cell configuration. Under voltage-clamp conditions,the amplitude of voltage-gated outward currents wasenhanced by the application of 100 lM histamine in 65%of amacrine cells. Histamine also increased the amplitudesof voltage-gated inward currents in 72% of amacrine cells.When antagonists of the histamine H1, H2, or H3 receptorswere applied to histamine-sensitive amacrine cells, allthree types of these inhibitors reduced the effect of histamine.Moreover, we classified recorded cells into seventypes based on their morphological characteristics. Two ofthe seven types, diffuse multistratified cells and AII amacrinecells, responded significantly to histamine. Theseresults indicate that histamine affected the membranepotential via three types of histamine receptors. Furthermore,there were differences in the responses to histamineamong types of amacrine cells. Histamine may be one ofthe important neurotransmitters and/or neuromodulators inthe visual processing.Keywords Retina Amacrine cell Histamine Patchclamptechnique Inward current Outward curren

Novel Technique for Retinal Nerve Cell Regeneration with Electrophysiological Functions Using Human Iris-Derived iPS Cells

Regenerative medicine in ophthalmology that uses induced pluripotent stem cells (iPS) cells has been described, but those studies used iPS cells derived from fibroblasts. Here, we generated iPS cells derived from iris cells that develop from the same inner layer of the optic cup as the retina, to regenerate retinal nerves. We first identified cells positive for p75NTR, a marker of retinal tissue stem and progenitor cells, in human iris tissue. We then reprogrammed the cultured p75NTR-positive iris tissue stem/progenitor (H-iris stem/progenitor) cells to create iris-derived iPS (H-iris iPS) cells for the first time. These cells were positive for iPS cell markers and showed pluripotency to differentiate into three germ layers. When H-iris iPS cells were pre-differentiated into neural stem/progenitor cells, not all cells became positive for neural stem/progenitor and nerve cell markers. When these cells were pre-differentiated into neural stem/progenitor cells, sorted with p75NTR, and used as a medium for differentiating into retinal nerve cells, the cells differentiated into Recoverin-positive cells with electrophysiological functions. In a different medium, H-iris iPS cells differentiated into retinal ganglion cell marker-positive cells with electrophysiological functions. This is the first demonstration of H-iris iPS cells differentiating into retinal neurons that function physiologically as neurons