Transmitter‐Like Release of Endogenous 3,4‐Dihydroxyphenylalanine from Rat Striatal Slices

Abstract

Biphasic electrical field stimulation (0.5–5 Hz, 2 ms, 25 V, 3 min) and high K⁺ (10–30 mM, 5 min) released endogenous 3,4‐dihydroxyphenylalanine (DOPA) from superfused rat striatal slices. Characteristics of the DOPA release were compared with those of 3,4‐dihydroxyphenylethylamine (dopamine, DA). Electrical stimulation at 2 Hz evoked DOPA and DA over similar time courses, α‐Methyl‐p‐tyrosine (0.2 mM) markedly reduced release of DOPA but not of DA. Maximal release (0.3 pmol) of DOPA was obtained at 2 Hz and at 15 mM K⁺. The impulse‐evoked release of DOPA and DA was completely tetrodotoxin (0.3 μM) sensitive and Ca²⁺ dependent and the 15 mM K⁺‐evoked release was also Ca²⁺ dependent. On l‐[3,5‐³H]tyrosine (1 μM) superfusion, high K⁺ (15 and 60 mM) released DOPA and DA together with concentration‐dependent decreases in tyrosine 3‐monooxygenase (EC 1.14.16.2) activity as indicated by [³H]H₂O formation, followed by concentration‐dependent increases after DOPA and DA release ended. These findings suggest that striatal DOPA is released by a Ca²⁺‐dependent excitation‐secretion coupling process similar to that involved in transmitter release.