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

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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.