title: Cobalt ions inhibit negative feedback in the outer retina by blocking hemichannels on horizontal cells.
abstract: In goldfish, negative feedback from horizontal cells to cones shifts the activation function of the Ca2+ current of the cones to more negative potentials. This shift increases the amount of Ca2+ flowing into the cones, resulting in an increase in glutamate release. The increased glutamate release forms the basis of the feedback-mediated responses in second-order neurons, such as the surround-induced responses of bipolar cells and the spectral coding of horizontal cells. Low concentrations of Co2+ block these feedback-mediated responses in turtle retina. The mechanism by which this is accomplished is unknown. We studied the effects of Co2+ on the cone/horizontal network of goldfish retina and found that Co2+ greatly reduced the feedback-mediated responses in both cones and horizontal cells in a GABA-independent way. The reduction of the feedback-mediated responses is accompanied by a small shift of the Ca2+ current of the cones to positive potentials. We have previously shown that hemichannels on the tips of the horizontal cell dendrites are involved in the modulation of the Ca2+ current in cones. Both the absence of this Co2+-induced shift of the Ca2+ current in the absence of a hemichannel conductance and the sensitivity of Cx26 hemichannels to low concentrations of Co2+ are consistent with a role for hemichannels in negative feedback from horizontal cells to cones.
authors.affiliation: Research Unit Retinal Signal Processing, The Netherlands Ophthalmic Research Institute, Amsterdam, The Netherlands.
authors.forename: I
authors.initials: I
authors.lastname: Fahrenfort
authors.forename: T
authors.initials: T
authors.lastname: Sjoerdsma
authors.forename: H
authors.initials: H
authors.lastname: Ripps
authors.forename: M
authors.initials: M
authors.lastname: Kamermans
mesh_terms: D000818:Animals; D003035:Cobalt / Q000494:pharmacology*; D004553:Electric Conductivity; D025461:Feedback, Physiological / Q000187:drug effects*; D006054:Goldfish; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000502:physiology; D007477:Ions; D012160:Retina / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000502:physiology
chemical_list: D007473:Ion Channels; D007477:Ions; D003035:Cobalt; D005680:gamma-Aminobutyric Acid