In this issue, two articles present major advances in the quantitative analysis of the molecular mechanisms underlying rod phototransduction. One is by Nikonov et al. (1998), the other by Calvert et al. (1998). These two papers are complimentary, but with substantial areas of intersection.
At the present time, the activation cascade in rod phototransduction that leads to the hydrolysis of the internal transmitter, cyclic GMP (cGMP) and to the closure of light-sensitive channels is fairly well understood. The inactivation steps responsible for the termination of the photoresponse and the feedback mechanisms, which modulate sensitivity and kinetics and also contribute to response termination, are not understood nearly as well. The field of phototransduction has always been fraught with controversy: for every point, there has been a counterpoint. However, one can argue, with little fear of inciting controversy, that a complete understanding of phototransduction must include an understanding of...
