Ca2(+)-evoked [3H]dopamine release from synaptosomes is dependent on neuronal type Ca2+ channels and is not mediated by acetylcholine, glutamate or aspartate release.
Elevation of potassium concentrations ([K+]) in the presence of Ca2+ is the most common method of evoking neurotransmitter release from synaptosomes. However, we have been investigating a method of releasing dopamine from synaptosomes that does not involve using elevated [K+]. In this paradigm of neurotransmitter release, dopamine is released from synaptosomes, previously exposed to micromolar or lower [Ca2+], by 1.25 mM Ca2+ in the presence of non-depolarizing [K+] (4.5 mM). The present experiments characterize the Ca2+ channel(s) involved in the Ca2(+)-evoked release of dopamine from synaptosomes, and determine whether the release is mediated by acetylcholine, glutamate or aspartate. omega-Conotoxin (10 nM), which blocks N-, L- and possibly T-type voltage-sensitive Ca2+ channels (VSCC), inhibited the Ca2(+)-evoked [3H]dopamine release from either striatal or olfactory tubercle synaptosomes to less than 50% of control. Neither 1 microM nifedipine nor 1 microM verapamil, which block L-type VSCC, affected Ca2(+)-evoked release. The N- and T-type VSCC blocker neomycin and the nonspecific Ca2+ antagonist, cobalt2+, inhibited release to a greater extent than omega-conotoxin. At 1 mM, both compounds inhibited release to approximately 30% of control. Neither the excitatory neurotransmitter glutamate nor aspartate (2mM) affected 1 microM LY-171555 (a dopamine D2 agonist) inhibition of Ca2(+)-evoked [3H]dopamine release. Also, the glutamate antagonist, glutamic acid diethyl ester, did not affect either Ca2(+)-evoked release or 1 microM LY-171555 inhibition thereof. The nicotinic antagonist hexamethonium (10 microM) and the muscarinic antagonist atropine (1 microM) were also ineffective in inhibiting Ca2(+)-evoked release or LY-171555 inhibition of release.(ABSTRACT TRUNCATED AT 250 WORDS)
Bowyer
J F
JF
Department of Pharmacology, University of Colorado Health Sciences Center, Denver.
Weiner
N
N
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology*; D001285:Atropine / Q000494:pharmacology; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects*; D003035:Cobalt / Q000494:pharmacology; D046508:Culture Techniques; D004298:Dopamine / Q000378:metabolism*; D004347:Drug Interactions; D005730:Ganglionic Blockers / Q000494:pharmacology; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D018738:Hexamethonium; D006584:Hexamethonium Compounds / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D051381:Rats; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism; D014700:Verapamil / Q000494:pharmacology
D015220:Calcium Channels; D005730:Ganglionic Blockers; D005971:Glutamates; D006584:Hexamethonium Compounds; D001224:Aspartic Acid; D018738:Hexamethonium; D003035:Cobalt; D018698:Glutamic Acid; D001285:Atropine; D014700:Verapamil; D009543:Nifedipine; D000109:Acetylcholine; D002118:Calcium; D004298:Dopamine