Calcium channels involved in the inhibition of acetylcholine release by presynaptic muscarinic receptors in rat striatum.
1. The mechanism of the inhibitory action of presynaptic muscarinic receptors on the release of acetylcholine from striatal cholinergic neurons is not known. We investigated how the electrically stimulated release of [3H]-acetylcholine from superfused rat striatal slices and its inhibition by carbachol are affected by specific inhibitors of voltage-operated calcium channels of the L-type (nifedipine), N-type (omega-conotoxin GVIA) and P/Q-type (omega-agatoxin IVA). 2. The evoked release of [3H]-acetylcholine was not diminished by nifedipine but was lowered by omega-conotoxin GVIA and by omega-agatoxin IVA, indicating that both the N- and the P/Q-type (but not the L-type) channels are involved in the release. The N-type channels were responsible for approximately two thirds of the release. The release was >97% blocked when both omega-toxins acted together. 3. The inhibition of [3H]-acetylcholine release by carbachol was not substantially affected by the blockade of the L- or P/Q-type channels. It was diminished but not eliminated by the blockade of the N-type channels. 4. In experiments on slices in which cholinesterases had been inhibited by paraoxon, inhibition of [3H]-acetylcholine release by endogenous acetylcholine accumulating in the tissue could be demonstrated by the enhancement of the release after the addition of atropine. The inhibition was higher in slices with functional N-type than with functional P/Q-type channels. 5. We conclude that both the N- and the P/Q-type calcium channels contribute to the stimulation-evoked release of acetylcholine in rat striatum, that the quantitative contribution of the N-type channels is higher, and that the inhibitory muscarinic receptors are more closely coupled with the N-type than with the P/Q-type calcium channels.
Dolezal
V
V
Institute of Physiology, Academy of Sciences, Vídenská 1083, 14220 Prague, Czechia.
Tucek
S
S
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D004294:Domperidone / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D006220:Haloperidol / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D017072:Neostriatum / Q000187:drug effects / Q000378:metabolism*; D010261:Paraoxon / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D051381:Rats; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*; D017661:Receptors, Presynaptic / Q000187:drug effects / Q000378:metabolism*; D013111:Spider Venoms / Q000494:pharmacology; D020867:omega-Agatoxin IVA; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002800:Cholinesterase Inhibitors; D018492:Dopamine Antagonists; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D010455:Peptides; D011976:Receptors, Muscarinic; D017661:Receptors, Presynaptic; D013111:Spider Venoms; D020867:omega-Agatoxin IVA; D004294:Domperidone; D001285:Atropine; D002217:Carbachol; D020866:omega-Conotoxin GVIA; D006220:Haloperidol; D000109:Acetylcholine; D010261:Paraoxon