Erg Responses in the Dystrophin Dp71-Null Mice

Abstract

Purpose: : The dystrophin Dp71 is the most abundant Duchenne Muscular Dystrophy (DMD) gene product expressed in the retina. This protein is localized in the Müller glial cells (MGC) and regulates the retinal homeostasis by clustering Kir4.1 and AQP4 channels. It is known that 80% of DMD patients and the mdx^3cv mouse strain with a mutation affecting all the DMD gene products show an increasing implicit time and a high attenuation of the b-wave amplitude. The aim of this study was to determine whether, solely the absence of Dp71 affects the electroretinogram (ERG) response.

Methods: : Ganzfeld ERGs were obtained from dark adapted Dp-71 null mice and wild-type littermates. Scotopic flash ERGs were recorded at different light intensities. Amplitudes and implicit times were measured for a-wave and b-wave. The b-wave sensitivity curves were fitted to calculate the saturated b-wave amplitude (Vmax) and the retinal sensitivity parameter (k). Oscillatory potentials (OP) were isolated by filtering the ERG responses. Photopic flash ERGs were recorded after 10 minutes of light adaptation. Photopic Flicker ERGs were obtained with light flashes.

Results: : The scotopic ERGs recorded from Dp-71 null mice showed normal a-wave amplitudes, but revealed a reduction in the b-wave amplitudes at the highest light intensities. Consequently, the b/a-wave amplitude ratio was smaller in Dp71-null mice compared with littermates. The Vmax value was reduced by 25%, but no change was found in the k parameter. Implicit times of the a-wave and b-wave were not different between Dp71-null mice and wild-types. The OP amplitudes and implicit times showed no difference between the two strains. No change was observed in the photopic ERG and flicker responses in Dp71-null mice compared with littermates.

Conclusions: : The absence of dystrophin Dp71 is associated with a reduction in b-wave amplitude of the dark-adapted ERG. This result suggests that Dp71 together with all the DMD gene products expressed in mouse retina may contribute to normal retinal electrophysiology.

Keywords: retina • Muller cells • electroretinography: non-clinical