Cyclic Nucleotide-gated Ion Channels in Rod Photoreceptors Are Protected from Retinoid Inhibition
| Autor: | Clint L. Makino, Sarah L. McCabe, Maureen E. Estevez, Quanhua He, Peter D. Calvert, Dmitriy Alexeev, Anita L. Zimmerman, M. Carter Cornwall, David E. Ong |
|---|---|
| Rok vydání: | 2006 |
| Předmět: |
Rhodopsin
Opsin Patch-Clamp Techniques Light genetic structures Physiology medicine.drug_class Cyclic Nucleotide-Gated Cation Channels Ambystoma Article Ion Channels Retinoids 03 medical and health sciences chemistry.chemical_compound 0302 clinical medicine 3' 5'-Cyclic-GMP Phosphodiesterases Retinal Rod Photoreceptor Cells 1-Methyl-3-isobutylxanthine medicine Animals Retinoid Patch clamp Vitamin A Cyclic GMP Ion channel 030304 developmental biology 0303 health sciences biology Retinoid binding protein Retinal Articles Rod Cell Outer Segment Retinol-Binding Proteins Biochemistry chemistry Guanylate Cyclase Microspectrophotometry Retinaldehyde biology.protein Biophysics sense organs Diterpenes Retinol-Binding Proteins Plasma 030217 neurology & neurosurgery Visual phototransduction |
| Zdroj: | The Journal of General Physiology |
| ISSN: | 1540-7748 0022-1295 |
| Popis: | In vertebrate rods, photoisomerization of the 11-cis retinal chromophore of rhodopsin to the all-trans conformation initiates a biochemical cascade that closes cGMP-gated channels and hyperpolarizes the cell. All-trans retinal is reduced to retinol and then removed to the pigment epithelium. The pigment epithelium supplies fresh 11-cis retinal to regenerate rhodopsin. The recent discovery that tens of nanomolar retinal inhibits cloned cGMP-gated channels at low [cGMP] raised the question of whether retinoid traffic across the plasma membrane of the rod might participate in the signaling of light. Native channels in excised patches from rods were very sensitive to retinoid inhibition. Perfusion of intact rods with exogenous 9- or 11-cis retinal closed cGMP-gated channels but required higher than expected concentrations. Channels reopened after perfusing the rod with cellular retinoid binding protein II. PDE activity, flash response kinetics, and relative sensitivity were unchanged, ruling out pharmacological activation of the phototransduction cascade. Bleaching of rhodopsin to create all-trans retinal and retinol inside the rod did not produce any measurable channel inhibition. Exposure of a bleached rod to 9- or 11-cis retinal did not elicit channel inhibition during the period of rhodopsin regeneration. Microspectrophotometric measurements showed that exogenous 9- or 11-cis retinal rapidly cross the plasma membrane of bleached rods and regenerate their rhodopsin. Although dark-adapted rods could also take up large quantities of 9-cis retinal, which they converted to retinol, the time course was slow. Apparently cGMP-gated channels in intact rods are protected from the inhibitory effects of retinoids that cross the plasma membrane by a large-capacity buffer. Opsin, with its chromophore binding pocket occupied (rhodopsin) or vacant, may be an important component. Exceptionally high retinoid levels, e.g., associated with some retinal degenerations, could overcome the buffer, however, and impair sensitivity or delay the recovery after exposure to bright light. |
| Databáze: | OpenAIRE |
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