Abstract
Responses to test flashes were recorded extracellularly from the aspartate-treated, isolated retina of the skate, before and after topical application to the retina of solutions containing GTP, ATP, or certain hydrolysis-resistant analogues. When applied to strongly light-adapted retinas (⩾ 87% bleached), the analogues p(CH 2)ppG, p(NH)ppG and p(CH 2)ppA induced sustained decreases in threshold of the PIII response. Similar treatment of light-adapted retinas with GTP or ATP also promoted decreases in threshold, but these changes appeared relatively transient. All of the test substances lacked significant activity when applied to dark-adapted (unbleached) retinas. The results are discussed in relation to other studies examining the effects of light on GTP- and ATP-dependent processes within the photoreceptors.
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