Desensitization of the mGluR6 transduction current in tiger salamander On bipolar cells

J Physiol. 2004 Jul 1;558(Pt 1):137-46. doi: 10.1113/jphysiol.2004.064980. Epub 2004 May 14.


Light depolarizes retinal On bipolar cells, opening the cation-selective channels that are responsible for producing the synaptic current. In this study, the basic features of light-induced signals were mimicked by bathing slices of salamander retina with an agonist for the mGluR6 receptor that is expressed on the dendrites of On cells, and then displacing the agonist with the mGluR6 antagonist (RS)-a-cyclopropyl-4-phosphonophenylglycine (CPPG). The transduction current that is activated by this protocol rapidly shuts off, or desensitizes. Desensitization was highly correlated with the concentration and the type of Ca2+ buffer that was dialysed into the cell: When Ca2+ buffering was minimized by dialysing cells with 0.5 mM EGTA, the steady-state response was reduced to approximately 40% of the peak response. Buffering with 10 mM EGTA reduced desensitization, while BAPTA completely eliminated it. Removing external Ca2+ also prevented desensitization, suggesting that entry of Ca2+ through the transduction channel provides the trigger. The time course of desensitization was measured by using a voltage jump protocol to rapidly increase Ca2+ influx, and could be fitted with a single time constant on the order of 1 s, in good agreement with previously published rates of desensitization to steps of light in this species. It is proposed that Ca(2+)-dependent shut-off of the On bipolar cell transduction current may contribute to the conversion of sustained to transient light responses that predominate in the inner retina.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Ambystoma
  • Animals
  • Calcineurin / metabolism
  • Calcium / metabolism
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2
  • Calcium-Calmodulin-Dependent Protein Kinases / metabolism
  • Chelating Agents / pharmacology
  • Egtazic Acid / pharmacology
  • Glutamic Acid / pharmacology
  • Glycine / analogs & derivatives*
  • Glycine / pharmacology
  • Ion Channel Gating / drug effects
  • Ion Channel Gating / physiology
  • Membrane Potentials / drug effects
  • Membrane Potentials / physiology
  • Receptors, Metabotropic Glutamate / agonists
  • Receptors, Metabotropic Glutamate / antagonists & inhibitors
  • Receptors, Metabotropic Glutamate / physiology*
  • Retina / cytology*
  • Retina / physiology*


  • Chelating Agents
  • Receptors, Metabotropic Glutamate
  • cyclopropyl-4-phosphonophenylglycine
  • metabotropic glutamate receptor 6
  • Glutamic Acid
  • Egtazic Acid
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2
  • Calcium-Calmodulin-Dependent Protein Kinases
  • Calcineurin
  • Calcium
  • Glycine