A reweighting of receptor mechanisms in the ground squirrel retina: PIII and B-wave spectral sensitivity functions

PIII and b-wave spectral sensitivity functions were measured under various adapted conditions in the 13-lined ground squirrel. The PIII was isolated by intravitreal injection of sodium l-aspartate. Under the conditions studied, the PIII spectral sensitivity function always fitted the absorption spectrum of a 518 ± 3 nm Dartnall nomogram. This suggests that of the three photoreceptors ('rod-like', 'blue' cone and 'green' cone) present in the 13-lined ground squirrel the green cones are the overwhelming majority. The dark-adapted b-wave had two components: a b₁-wave with a spectral sensitivity that fitted a 516 ± nm Dartnall nomogram and a b₂-wave with a spectral sensitivity that fitted a 502 ± 4 nm Dartnall nomogram. The light-adapted b-wave had a spectral sensitivity that fitted a 516 ± 2 nm Dartnall nomogram.