Abstract
After prolonged visual adaptation of Drosophila, dramatic long-term changes of in vitro phosphorylation of a 50-kDa brain protein that is identical to the Ca2+/calmodulin-dependent protein kinase (EC 2.7.1.37) can be measured in isolated heads. By selective receptor cell desensitization in blue light, subcellular distribution of the 50-kDa kinase in fly brain is modified, and Ca2+-stimulated in vitro phosphorylation is increased. Concomitantly the 50-kDa kinase is translocated by in vitro phosphorylation from the membrane-cytoskeleton complex into the cytoplasm. After adaptation, association of the enzyme to the membrane shows long-term modification. In yellow light, which reverts receptor cell adaptation within seconds, the changes in kinase activity and distribution remain for about 2 hr, corresponding to the duration of behavioral modification induced by blue light. Reducing protein synthesis with cycloheximide inhibits the induction of behavioral modification as well as the prolonged modulation of the 50-kDa kinase by blue light. From our simple assay to measure biochemical changes induced in the intact organism by sensory stimulation, we propose that Ca2+/calmodulin-dependent kinase II is involved in long-term modulation of synaptic transmission.