Abstract

The rising phase of the rod photocurrent response to a brief flash is approximated by the ERG a-wave leading edge at intensities high enough to approach rate-of-rise saturation and to minimize interference from the inner retinal (b-wave) component.¹ Representation of the stages of the cGMP rising phase by a series of differential equations, as proposed by Cobbs and Pugh,² provides a means for interpreting the photocurrent response of rods and the leading edge of the a-wave in biochemical terms at high intensities [ARVO 32(4): 1276, 1991]. At low flash intensities the activation time course of PDE is well approximated by a delayed ramp. When the PDE ramp is combined with the equations for cGMP hydrolysis and cGMP channel activation, the rising phase is predicted to be a Gaussian. Lamb and Pugh [ARVO 32(4):1170, 1991] confirmed a number of predictions derived from the Gaussian rise in salamander rods for flashes producing up to 10⁵ isomerizations (out of 4 × 10⁹ rhodopsins). We apply the Gaussian representation of the photocurrent rising phase to human a-wave leading edges and evaluate the limitations of the fit against the salamander results and the more general Cobbs and Pugh representation as a function of intensity.

© 1991 Optical Society of America