PROTEIN-CONTENT AND CAMP-DEPENDENT PHOSPHORYLATION OF FRACTIONATED WHITE PERCH RETINA

In the retinas of teleost fish dopamine, released from interplexiform cells, modulates synaptic transmission at both the chemical and electr ical synapses of retinal horizontal cells. This modulation is due to a ctivation of adenylate cyclase and phosphorylation by protein kinase A , perhaps of the synaptic ion channel proteins themselves. In this stu dy we have fractionated the white perch retina by Percoll density grad ient centrifugation in order to identify proteins which coenrich with horizontal cells. In addition we have tested retinal fractions for pho sphorylation by native cAMP-dependent kinase. Our findings indicate th at there are at least 3 proteins of molecular weights 28, 43/44 and 50 kDa which coenrich with horizontal cells and 3 proteins of 30/31 kDa, 35 kDa (putative rhodopsin) and 48 kDa (putative arrestin) which coen rich with photoreceptor fractions. The 43/44 kDa phosphoprotein is a t arget for cAMP-dependent protein phosphorylation and thus is apparentl y an element of the dopaminergic modulatory pathway in perch horizonta l cells.