An estimate of image quality in the rat eye

the hyperpolarization of cones. This proposal together with the suggestion that barium ions reduce the potassium efflux in cones predicts that the receptor potential amplitude of cones should decline in the presence of barium. Such a decrease is noted in this study and elsewhere. Also consistent with this interpretation is our present finding that barium ions delay the onset of rapid dark adaptation but that the rate of recovery, once begun, is unaffected. The onset of this adaptation process is highly temperature-sensitive and therefore may represent an enzymatic process which removes the blocking agent or the inhibitory substance from the sodium channels. It is not unreasonable that barium may act directly on this proposed enzymatic process so as to impede the removal of the sodium channel inactivator. Such a possibility is not remote since barium is known to affect enzyme systems.' 15 Because the onset of the adaptation process in rods is also postulated to be governed by the enzymatic removal of an inactivator from the sodium channels, we anticipate that barium ions will increase the latency of the recovery process in rods as well. Research in our laboratory is currently under way to test this hypothesis.