April 2009
Volume 50, Issue 13
ARVO Annual Meeting Abstract  |   April 2009
Glutamate Mediates Cross-Talk Between Mammalian Cone Photoreceptors
Author Affiliations & Notes
  • B. A. Szmajda
    Department of Ophthalmology - Research, Northwestern University, Chicago, Illinois
  • S. H. DeVries
    Department of Ophthalmology - Research, Northwestern University, Chicago, Illinois
  • Footnotes
    Commercial Relationships  B.A. Szmajda, None; S.H. DeVries, None.
  • Footnotes
    Support  NIH Grants EY12141, EY07128
Investigative Ophthalmology & Visual Science April 2009, Vol.50, 6148. doi:
  • Views
  • Share
  • Tools
    • Alerts
      This feature is available to authenticated users only.
      Sign In or Create an Account ×
    • Get Citation

      B. A. Szmajda, S. H. DeVries; Glutamate Mediates Cross-Talk Between Mammalian Cone Photoreceptors. Invest. Ophthalmol. Vis. Sci. 2009;50(13):6148.

      Download citation file:

      © ARVO (1962-2015); The Authors (2016-present)

  • Supplements

Purpose: : Independent signaling by the tightly-packed foveal cones is important for high acuity and chromatic vision. Cone terminals are ensheathed by Müller glial cell processes, which presumably act to limit the lateral diffusion of glutamate. Cones, however, may potentially release up to 400 docked vesicles (20 ribbons, with 20 vesicles docked per ribbon) during repolarization after a light step. We used the cone glutamate transporter Cl- conductance to test whether the glutamate released by one cone could spill-over to neighboring cones.

Methods: : Patch-clamp studies were done in the cone-dominant ground squirrel. Adjacent cones were voltage-clamped in a slice or wholemount preparation. One cone, the ‘donor’, was stepped from -70 mV to 0 mV to elicit glutamate release. We measured the current response in an adjacent ‘acceptor’ cone held at a constant voltage, typically -70 mV. Patch pipette solutions contained Gramicidin D during experiments in which it was necessary to maintain the intracellular Cl- concentration. Values are expressed as mean ± S.D.

Results: : Stimulating a cone to release glutamate elicited a two-component response in a neighboring, unstimulated cone: a fast response component, resulting from cone-cone electrical coupling, and a slow component. The slow component could be blocked in three ways: by Co2+ and Cd2+-containing external solution (n = 3), when Cs+ was substituted for Na+ in the external solution (n = 2), or by glutamate transporter blockers (TBOA: 76.0 ± 9.7% block, n = 11; THA: 95.6 ± 9.8%, n = 5). The results suggest that the slow component is mediated by glutamate ‘spillover’ from the donor cone, causing the activation of a glutamate transporter Cl- conductance in the acceptor cone. In experiments with matched internal and external Cl-, acceptor cone currents had mean amplitudes of -8.5 ± 7.2 pA (range = 0-31 pA, n = 39), 20-80 rise times of 5.9 ± 1.9 ms, and were often bidirectional. Acceptor cone currents were increased by four to eight-fold when SCN- was substituted for Cl- in the pipette solution. The transporter current reversed at -26.8 ± 14.0 mV (n = 10).

Conclusions: : We have observed a cross-talk between cone photoreceptors that is mediated by a glutamate transporter Cl- conductance. A transporter reversal potential of approximately -30 mV is consistent with an excitatory role for cone-cone chemical transmission.

Keywords: photoreceptors • synapse • electrophysiology: non-clinical 

This PDF is available to Subscribers Only

Sign in or purchase a subscription to access this content. ×

You must be signed into an individual account to use this feature.