STEADY-STATE FEEDBACK IN MAMMALIAN PHOTOTRANSDUCTION ILLUSTRATED BY A NOMOGRAM

Published data characterizing the four reactions responsible for the Ca2+-mediated negative feedback in mammalian rod phototransduction were used to generate graphs which are combined in a circular fashion so that the y-axis of one serves as the x-axis of the next. The nomogram thus created makes it possible to determine by inspection the steady state situation in darkness, and tbe quasi-steady state situations that pertain shortly after exposure to light of different intensities. The results predicted by the nomogram suggest that Ca2+-mediated negative feedback is responsible for the Weber-Fechner relationship between stimulus and response.