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R.J. Salvi, W. Sun, D. Ding, J. Wang, L. Campbell, G.M. Seigel; R28 Retinal Precursor Cells Express Functional Neurotransmitter Receptors and Co-Localize to Neural Zones Within Inner Ear Cultures . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1682.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Immortalized R28 rat retinal precursor cells represent an inexhaustible supply of graft material that might be used to replace damaged sensory cells or neurons. The propensity of transplanted R28 cells to differentiate and integrate into host tissue is likely to depend on extrinsic cues in the environment acting on receptors in transplanted cells. The purpose of this study was to assess the neurophysiological responses of R28 retinal precursor cells and their ability to integrate into inner ear cultures containing neurons and sensory hair cells. Methods: To identify potential signaling mechanisms, we used whole-cell patch clamp recordings and immunolabeling techniques to identify voltage-gated and ligand gated channels on proliferating R28 progenitors. Co–cultures of R28 cells and inner ear cultures were used to assess the neuronal integration potential of R28 precursor cells. Results: Action potentials and voltage sensitive currents were largely absent from R28 cells suggesting that these cells are electrically quiescent when cultured in isolation. Interestingly, R28 cells responded to many neurotransmitter agonists. Both non-NMDA and NMDA receptor agonists induced inward currents in most R28 cells. The mean inward current was -105+ 81 pA for kainic acid (KA, 200 µM, -70+8 pA for AMPA (200 µM) and -43+31 pA for NMDA (1 mM). KA and AMPA induced currents were suppressed by CNQX and DNQX. GABA (200 µM), muscimol (500 µM) and baclofen (500 µM) induced currents with mean amplitudes of -53+28 pA, -40+17 pA and -23+8 pA, respectively. In some cells, small, but significant inward currents were induced by glycine (-31.9+18 pA, 14/48), ACh (-11.2+7.7 pA, 10/38) and ATP (-16+19 pA, 16/50). Immunocytochemistry revealed the presence of GluR1-3, NMDA, GABAa, glycine and ACh receptors consistent with physiological results. The diversity of neurotransmitter receptors suggests that R28 progenitors might be ued as neural replacements in damaged inner ears. To evaluate this hypothesis, DiI-labeled R28 cells were transplanted to inner ear cultures. Interestingly, R28 cells preferentially co-localized to neuronal areas, but seldom appeared within or lateral to the sensory cell region of Corti's organ. Conclusions: R28 retinal progenitor cells possess functional neurotransmitter receptors and can co-localize to neuronal areas of inner ear cultures. These results suggest that R28 progenitor cells may have the potential to differentiate into spiral ganglion-like neurons in vivo.
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