UPTAKE AND RELEASE OF [DOPAMINE-H-3 IN THE GOLDFISH RETINA

Abstract— The uptake and release of [3H]dopamine was studied in the goldfish retina with the following results: (1) when goldfish retinas were incubated with 2 ± 10‐7m‐[3H]dopamine for less than 20min and processed for autoradiography. most of the label was associated with dopaminergic terminals that contact certain horizontal cells. Biochemical analysis showed that > 93% of this label was [3H]‐dopamine. (2) [3H]dopamine uptake saturated with increasing dopamine concentration and followed Michaelis‐Menten kinetics. This uptake could be explained by a single ‘high‐affinity’ mechanism with a Km of 2.61 ± 0.41 ± 10‐7m and a Vmax of 66 ± 12 ± 10‐12 mol/min/mg protein. (3) [3H]dopamine uptake was temperature‐dependent with a temperature coefficient of 1.7 and an energy of activation of 11.4 kcal/mol. (4) The initial rate of uptake was unaffected by the absence of Ca2+ or the presence of Co2+; however, more than 85, uptake was blocked in the absence of external Na+. (5) Neither 1 mm‐cyanide nor 5 mm‐iodoacetate blocked more than 30% of uptake individually; however, in combination > 70% of uptake was blocked. (6) Centrally acting drugs benztropine and diphenylpyraline inhibited at least 60–70% of [3H]dopamine uptake. (7) [3H]dopamine in the retina could be released by increasing the external K+ concentration. This release was Ca2+ ‐dependent and was blocked by 10mm‐Co2+ or 2Omm‐Mg2+. The amount of [3H]dopamine released was not affected by the presence of benztropine, diphenylpyraline or fluphenazine in the incubation medium. These studies add further support for dopamine as a neurotransmitter used by interplexiform cells of the goldfish retina. Copyright © 1979, Wiley Blackwell. All rights reserved