Chappell Richard L.

No Thumbnail Available
Last Name
Chappell
First Name
Richard L.
ORCID

Filters

2004 - 2009 2 2010 - 2014 1
3
3
Reset filters

Settings

Search Results

Now showing 1 - 3 of 3
  • Article
    Potassium currents distinguish the two subtypes of morphologically distinct skate bipolar cells
    (Marine Biological Laboratory, 2004-12) Qian, Haohua ; Chappell, Richard L. ; Redenti, Stephen ; Ripps, Harris
    Bipolar cells in the vertebrate retina are second-order neurons that convey visual information from photoreceptors to ganglion cells, the neurons that relay the message to the brain. Bipolar cells consist typically of multiple subtypes that differ in their morphology, synaptic connections, and response properties. The individual subtypes are thought to carry different aspects of the visual signal through the retina, and they often exhibit unique membrane properties and neurotransmitter receptors. In the all-rod skate retina, only two morphologically and pharmacologically distinct subtypes of bipolar cell have been identified thus far. The large-field bipolar cells, with extensive dendritic arbors, are glycine-insensitive, whereas the small-field bipolar cells, which have only one or two dendritic branches, are sensitive to glycine. In the present study, we explored further the membrane properties of these two subtypes of skate bipolar cell with emphasis on the voltage-sensitive potassium currents. Our results show that the cells exhibit different voltage-activated current profiles, suggesting that the signals they transmit contain different features of the visual scene.
  • Article
    Histidine suppresses zinc modulation of connexin hemichannels
    (Marine Biological Laboratory, 2004-12) Chappell, Richard L. ; Qian, Haohua ; Zakevicius, Jane ; Ripps, Harris
    Zinc has been shown to modulate hemichannel currents of connexins Cx35 and Cx38 in Xenopus oocytes. In both cases the effects were biphasic; i.e., low concentrations of zinc enhanced, whereas higher concentrations decreased, the magnitudes of the voltage-activated hemichannel currents. The present study was designed to determine the effects of zinc on hemichannels formed by Cx26, a connexin reportedly expressed on dendrites of carp horizontal cells and implicated in a mechanism for photoreceptor feedback. In addition, we examined whether histidine, a zinc chelator, would block the action of zinc on Cx26 hemichannel currents, or would exert a direct effect on those currents.
  • Article
    Review : Zinc’s functional significance in the vertebrate retina
    (Molecular Vision, 2014-07-31) Ripps, Harris ; Chappell, Richard L.
    This review covers a broad range of topics related to the actions of zinc on the cells of the vertebrate retina. Much of this review relies on studies in which zinc was applied exogenously, and therefore the results, albeit highly suggestive, lack physiologic significance. This view stems from the fact that the concentrations of zinc used in these studies may not be encountered under the normal circumstances of life. This caveat is due to the lack of a zinc-specific probe with which to measure the concentrations of Zn2+ that may be released from neurons or act upon them. However, a great deal of relevant information has been garnered from studies in which Zn2+ was chelated, and the effects of its removal compared with findings obtained in its presence. For a more complete discussion of the consequences of depletion or excess in the body’s trace elements, the reader is referred to a recent review by Ugarte et al. in which they provide a detailed account of the interactions, toxicity, and metabolic activity of the essential trace elements iron, zinc, and copper in retinal physiology and disease. In addition, Smart et al. have published a splendid review on the modulation by zinc of inhibitory and excitatory amino acid receptor ion channels.