Hemichannel-Mediated and pH-Based Feedback from Horizontal Cells to Cones in the Vertebrate Retina

Background Recent studies designed to identify the mechanism by which retinal horizontal cells communicate with cones have implicated two processes. According to one account, horizontal cell hyperpolarization induces an increase in pH within the synaptic cleft that activates the calcium current (Ca2+-current) in cones, enhancing transmitter release. An alternative account suggests that horizontal cell hyperpolarization increases the Ca2+-current to promote transmitter release through a hemichannel-mediated ephaptic mechanism. Methodology/Principal Findings To distinguish between these mechanisms, we interfered with the pH regulating systems in the retina and studied the effects on the feedback responses of cones and horizontal cells. We found that the pH buffers HEPES and Tris partially inhibit feedback responses in cones and horizontal cells and lead to intracellular acidification of neurons. Application of 25 mM acetate, which does not change the extracellular pH buffer capacity, does lead to both intracellular acidification and inhibition of feedback. Because intracellular acidification is known to inhibit hemichannels, the key experiment used to test the pH hypothesis, i.e. increasing the extracellular pH buffer capacity, does not discriminate between a pH-based feedback system and a hemichannel-mediated feedback system. To test the pH hypothesis in a manner independent of artificial pH-buffer systems, we studied the effect of interfering with the endogenous pH buffer, the bicarbonate/carbonic anhydrase system. Inhibition of carbonic anhydrase allowed for large changes in pH in the synaptic cleft of bipolar cell terminals and cone terminals, but the predicted enhancement of the cone feedback responses, according to the pH-hypothesis, was not observed. These experiments thus failed to support a proton mediated feedback mechanism. The alternative hypothesis, the hemichannel-mediated ephaptic feedback mechanism, was therefore studied experimentally, and its feasibility was buttressed by means of a quantitative computer model of the cone/horizontal cell synapse. Conclusion We conclude that the data presented in this paper offers further support for physiologically relevant ephaptic interactions in the retina.

[1]  Andrey V Dmitriev,et al.  Electrical feedback in the cone pedicle: a computational analysis. , 2006, Journal of neurophysiology.

[2]  P. Witkovsky,et al.  Sub-millimolar cobalt selectively inhibits the receptive field surround of retinal neurons , 1999, Visual Neuroscience.

[3]  D. Paul,et al.  Connexin46, a novel lens gap junction protein, induces voltage-gated currents in nonjunctional plasma membrane of Xenopus oocytes , 1991, The Journal of cell biology.

[4]  H. Spekreijse,et al.  Horizontal cells feed back to cones by shifting the cone calcium-current activation range , 1996, Vision Research.

[5]  G. Sharp,et al.  Intracellular pH plays a critical role in glucose-induced time-dependent potentiation of insulin release in rat islets. , 2002, Diabetes.

[6]  R. Hanitzsch,et al.  The influence of HEPES on light responses of rabbit horizontal cells , 2001, Vision Research.

[7]  Akimichi Kaneko,et al.  pH Changes in the Invaginating Synaptic Cleft Mediate Feedback from Horizontal Cells to Cone Photoreceptors by Modulating Ca2+ Channels , 2003, The Journal of general physiology.

[8]  S. Mangel,et al.  Retinal pH reflects retinal energy metabolism in the day and night. , 2004, Journal of neurophysiology.

[9]  M. Kamermans,et al.  Cobalt ions inhibit negative feedback in the outer retina by blocking hemichannels on horizontal cells , 2004, Visual Neuroscience.

[10]  S. Wu,et al.  Synaptic transmission in the outer retina. , 1994, Annual review of physiology.

[11]  S. Barnes,et al.  Modulation of transmission gain by protons at the photoreceptor output synapse. , 1993, Proceedings of the National Academy of Sciences of the United States of America.

[12]  M Kamermans,et al.  Hemichannel-Mediated Inhibition in the Outer Retina , 2001, Science.

[13]  H Spekreijse,et al.  The dynamic characteristics of the feedback signal from horizontal cells to cones in the goldfish retina , 2001, The Journal of physiology.

[14]  P. Witkovsky,et al.  Feedback from luminosity horizontal cells mediates depolarizing responses of chromaticity horizontal cells in the Xenopus retina. , 1995, Proceedings of the National Academy of Sciences of the United States of America.

[15]  GABAergic Modulation of Ephaptic Feedback in the Outer Retina , 2002 .

[16]  M. Chesler.  Regulation and modulation of pH in the brain. , 2003, Physiological reviews.

[17]  D. Copenhagen,et al.  Modulation of a sustained calcium current by intracellular pH in horizontal cells of fish retina , 1993, The Journal of general physiology.

[18]  Court Hull,et al.  Synaptic Cleft Acidification and Modulation of Short-Term Depression by Exocytosed Protons in Retinal Bipolar Cells , 2003, The Journal of Neuroscience.

[19]  D. Baylor,et al.  Receptive fields of cones in the retina of the turtle , 1971, The Journal of physiology.

[20]  A. L. Byzov,et al.  Electrical feedback mechanism in the processing of signals in the outer plexiform layer of the retina , 1986, Vision Research.

[21]  J. Klooster,et al.  Localization of the AMPA subunit GluR2 in the outer plexiform layer of goldfish retina , 2001, The Journal of comparative neurology.

[22]  H Spekreijse,et al.  The open- and closed-loop gain-characteristics of the cone/horizontal cell synapse in goldfish retina. , 2000, Journal of neurophysiology.

[23]  G. Nahas.  The pharmacology of tris(hydroxymethyl) aminomethane (THAM). , 1962, Pharmacological Reviews.

[24]  Maarten Kamermans,et al.  Retinal horizontal cell‐specific promoter activity and protein expression of zebrafish connexin 52.6 and connexin 55.5 , 2007, The Journal of comparative neurology.

[25]  J. Jefferys,et al.  Nonsynaptic modulation of neuronal activity in the brain: electric currents and extracellular ions. , 1995, Physiological reviews.

[26]  W. Stell,et al.  Color‐specific interconnections of cones and horizontal cells in the retina of the goldfish , 1975, The Journal of comparative neurology.

[27]  William H Baldridge,et al.  Proton-Mediated Feedback Inhibition of Presynaptic Calcium Channels at the Cone Photoreceptor Synapse , 2005, The Journal of Neuroscience.

[28]  R. Weiler,et al.  Light-dependent change of cone-horizontal cell interactions in carp retina , 1984, Brain Research.

[29]  W. Sly,et al.  Carbonic anhydrase XIV identified as the membrane CA in mouse retina: strong expression in Müller cells and the RPE. , 2005, Experimental eye research.

[30]  C. Bevans,et al.  Regulation of Connexin Channels by pH , 1999, The Journal of Biological Chemistry.

[31]  B. S. Winkler.  Buffer dependence of retinal glycolysis and ERG potentials. , 1986, Experimental eye research.

[32]  H. Qian,et al.  Evidence for hemi‐gap junctional channels in isolated horizontal cells of the skate retina , 1993, Journal of neuroscience research.

[33]  D. Kullmann,et al.  Geometric and viscous components of the tortuosity of the extracellular space in the brain. , 1998, Proceedings of the National Academy of Sciences of the United States of America.

[34]  H. Qian,et al.  Pharmacological enhancement of hemi-gap-junctional currents in Xenopus oocytes , 2002, Journal of Neuroscience Methods.

[35]  K. Tornqvist,et al.  Modulation of cone horizontal cell activity in the teleost fish retina. II. Role of interplexiform cells and dopamine in regulating light responsiveness , 1988, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[36]  M. Kamermans,et al.  Postsynaptic localization of γ‐aminobutyric acid transporters and receptors in the outer plexiform layer of the goldfish retina: An ultrastructural study , 2004, The Journal of comparative neurology.

[37]  Daniel J. Muller,et al.  Aminosulfonate Modulated pH-induced Conformational Changes in Connexin26 Hemichannels* , 2007, Journal of Biological Chemistry.

[38]  M. Bennett,et al.  Rapid and Direct Effects of pH on Connexins Revealed by the Connexin46 Hemichannel Preparation , 1999, The Journal of general physiology.

[39]  W. Sly,et al.  Carbonic anhydrase XIV is enriched in specific membrane domains of retinal pigment epithelium, Müller cells, and astrocytes , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[40]  D. Copenhagen,et al.  Intracellular Alkalinization Enhances Inward Rectifier K+ Current in Retinal Horizontal Cells of Catfish , 1995, Zoological science.

[41]  C. Nicholson,et al.  Ion diffusion modified by tortuosity and volume fraction in the extracellular microenvironment of the rat cerebellum. , 1981, The Journal of physiology.

[42]  H. Spekreijse,et al.  The Nature of Surround-Induced Depolarizing Responses in Goldfish Cones , 2000, The Journal of general physiology.

[43]  M Kamermans,et al.  The involvement of glutamate-gated channels in negative feedback from horizontal cells to cones. , 2005, Progress in brain research.

[44]  K. Tornqvist,et al.  Modulation of cone horizontal cell activity in the teleost fish retina. I. Effects of prolonged darkness and background illumination on light responsiveness , 1988, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[45]  H. von Gersdorff,et al.  Prolonged Reciprocal Signaling via NMDA and GABA Receptors at a Retinal Ribbon Synapse , 2005, The Journal of Neuroscience.

[46]  C. Nicholson,et al.  Extracellular space structure revealed by diffusion analysis , 1998, Trends in Neurosciences.

[47]  S. Wu,et al.  Input-output relations of the feedback synapse between horizontal cells and cones in the tiger salamander retina. , 1991, Journal of neurophysiology.

[48]  W. Thoreson,et al.  Feedback from Horizontal Cells to Rod Photoreceptors in Vertebrate Retina , 2008, The Journal of Neuroscience.

[49]  C. M. Davenport,et al.  Effects of pH Buffering on Horizontal and Ganglion Cell Light Responses in Primate Retina: Evidence for the Proton Hypothesis of Surround Formation , 2008, The Journal of Neuroscience.

[50]  H Spekreijse,et al.  The feedback pathway from horizontal cells to cones A mini review with a look ahead , 1999, Vision Research.

[51]  K. Tornqvist,et al.  Modulation of cone horizontal cell activity in the teleost fish retina. III. Effects of prolonged darkness and dopamine on electrical coupling between horizontal cells , 1988, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[52]  W. Sly,et al.  Expression of membrane-associated carbonic anhydrase XIV on neurons and axons in mouse and human brain. , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[53]  M. Tachibana.  Ionic currents of solitary horizontal cells isolated from goldfish retina. , 1983, The Journal of physiology.

[54]  A. Watson,et al.  Epithelial barrier function in vivo is sustained despite gaps in epithelial layers. , 2005, Gastroenterology.

[55]  S. DeVries,et al.  Exocytosed Protons Feedback to Suppress the Ca2+ Current in Mammalian Cone Photoreceptors , 2001, Neuron.

[56]  R. Keynes.  The ionic channels in excitable membranes. , 1975, Ciba Foundation symposium.

[57]  G. Somjen,et al.  Differential sensitivity to intracellular pH among high- and low-threshold Ca2+ currents in isolated rat CA1 neurons. , 1997, Journal of neurophysiology.

[58]  Gero Miesenböck,et al.  Visualizing secretion and synaptic transmission with pH-sensitive green fluorescent proteins , 1998, Nature.

[59]  T. Maren,et al.  Carbonic anhydrase: chemistry, physiology, and inhibition. , 1967, Physiological reviews.

[60]  Masahiro Yamada,et al.  Strongly pH-Buffered Ringer's Solution Expands the Receptive Field Size of Horizontal Cells in the Carp Retina , 2008, Zoological science.

[61]  W. Thoreson,et al.  Feedback effects of horizontal cell membrane potential on cone calcium currents studied with simultaneous recordings. , 2006, Journal of neurophysiology.

[62]  M. Piccolino,et al.  Sustained feedback effects of L-horizontal cells on turtle cones , 1980, Proceedings of the Royal Society of London. Series B. Biological Sciences.

[63]  M. Tachibana,et al.  Submillisecond Kinetics of Glutamate Release from a Sensory Synapse , 1998, Neuron.

[64]  D. A. Burkhardt,et al.  Effects of synaptic blocking agents on the depolarizing responses of turtle cones evoked by surround illumination , 1990, Visual Neuroscience.

[65]  B. Oakley,et al.  Extracellular pH in the isolated retina of the toad in darkness and during illumination. , 1989, The Journal of physiology.

[66]  A. Kaneko,et al.  GABA-mediated component in the feedback response of turtle retinal cones , 2005, Visual Neuroscience.

[67]  S. L. Jindal,et al.  Clinical Physiology of Acid—Base and Electrolyte Disorders. , 1978 .

[68]  H Spekreijse,et al.  Color opponency in cone-driven horizontal cells in carp retina. Aspecific pathways between cones and horizontal cells , 1991, The Journal of general physiology.