Investigation of Dopamine Content, Synthesis, and Release in the Rabbit Retina In Vitro: II. Effects of High Potassium, Adenylate Cyclase Activators, and N‐n‐Propyl‐3‐(3‐Hydroxyphenyl) Piperidine

Abstract The modulation of 3,4‐dihydroxyphenylethylamine (dopamine, DA) synthesis and release in rabbit retina in vitro by high K⁺; adenylate cyclase activators such as forskolin, 2‐chloroadenosine, vasoactive intestinal polypeptide (VIP); and the putative DA autoreceptor agonist N‐n‐propyl‐3‐(3‐hydroxyphenyl) piperidine (3‐PPP) has been investigated. Incubation of retinas in 50 mM K⁺ resulted in the activation of tyrosine hydroxylase (TH). Activation did not require the presence of extracellular Ca²⁺. K⁺ 50 mM also induced a Ca²⁺‐dependent release of DA. Forskolin 50 μM stimulated TH but 100 μM 2‐chloroadenosine and 650 μM VIP did not. Individually, (±)‐3‐PPP, (‐)‐3‐PPP, and (±)‐3‐PPP reduced DA synthesis and increased its release. The effects of (+)‐3‐PPP were dose‐dependent and did not require the presence of extracellular Ca²⁺. The activation of TH induced by 50 mM K⁺, but not that induced by 50 μM forskolin, was abolished by 100 μM (±)‐3‐PPP.