Role of Ca2+-Dependent Currents in the Recovery Phase of Rod ERG Dim-Flash Responses

Abstract

Purpose: : The electroretinogram (ERG) is a field potential that is generated by several current dipoles (source/sink pairs) within the retina. Our previous studies have suggested that the fast negative peak ("nose"¹) in saturated mouse ERG photoresponses is generated by voltage-dependent h- and K_x channels in rod inner segment^2,3. In this study we investigate the current sources/sinks that might affect the recovery phase of the mouse rod dim-flash ERG responses.

Methods: : Photoresponses to flashes (2 - 20 ms) were recorded with the ERG technique across isolated mouse (Mus musculus) retinas. The b-wave and higher-order neuron components were blocked by 2 mM aspartate or 0.05 mM APB. The glial component (slow PIII) was removed by BaCl₂.

Results: : Rod responses to dim flashes sometimes include a secondary negative wave. This wave was always present and greatly amplified when the rods were loaded with the intracellular Ca²⁺ buffer BAPTA(-AM). The secondary wave of dim-flash responses present in BAPTA-loaded rods could be abolished by the Ca²⁺ channel blocker Cd²⁺ (0.1 mM).

Conclusions: : The removal of the secondary wave of dim-flash responses by Cd²⁺ suggests that the Ca²⁺-activated channels (K⁺ or Cl^- channels) may affect the recovery phase of the ERG signal.¹Arden G.B. (1976), J. Physiol. 256(2):333-360²Vinberg F. & Koskelainen A. (2009), Invest. Ophthalmol. Vis. Sci. 50: E- Abstract 2175³Vinberg F., Strandman S. & Koskelainen (2009), J. Vis. 9(12):9.1-17

Keywords: electroretinography: non-clinical • calcium • ion channels