Rapid dark adaptation of bullfrog rods is delayed by barium

With use of sodium aspartate, the late receptor potential of the excised, perfused bullfrog retina was isolated. By means of a two-flash technique, rapid dark adaptation of rods was monitored. As in cones, barium ions were found to delay the onset of rapid dark adaptation of rods, but the rate of recovery, once begun, was virtually unaffected. The effect of barium on the amplitude-intensity relationship of rods was also determined. Unlike its ability to dramatically increase the amplitude of the receptor potential of rods, barium had no effect on the absolute threshold of rods. We propose that barium ions act on the enzyme system postulated to govern the onset of rapid dark adaptation of rods and suggest that a reduction in the activity of an ATP protein kinase might be the basis for this effect.