Newly synthesized and preformed acetylcholine are released from Torpedo synaptosomes by different pathways.

In this study, we investigated the mechanisms underlying the release of preformed and of newly synthesized acetylcholine (ACh) from isolated Torpedo nerve terminals (synaptosomes). This was pursued by examining and comparing the effects of anticytoskeletal and anticalmodulin drugs and of activating the presynaptic muscarinic ACh receptors on the release of preformed endogenous ACh and of newly synthesized radiolabeled ACh. The anticytoskeletal drugs vinblastine, cytochalasin B, and colchicine inhibit the Ca2+-dependent K+-mediated release of newly synthesized radiolabeled ACh, but have no effect on the release of preformed ACh.

Seasonal variations in the muscarinic regulation of acetylcholine release from Torpedo electric organ nerve terminals.

The cholinergic nerve endings of the electric organs of Torpedo ocellata contains presynaptic muscarinic acetylcholine receptors (mAChR) which regulate acetylcholine (ACh) release by negative feedback. The efficiency of this muscarinic regulation varies circannually: maximal inhibition is observed in the winter, much smaller effects in the fall and spring, and no effect is observed during the summer. These variations are accompanied by seasonal changes in the ability of the mAChR to trigger the synthesis of its second messenger (a prostaglandin E-like substance) and in the ability of exogenous prostaglandin E2 to inhibit ACh release.

Metabolism of arachidonic acid and prostaglandins in the Torpedo electric organ: modulation by the presynaptic muscarinic acetylcholine receptor.

We have found that Torpedo electric organ readily synthesizes prostaglandin E2 from both exogenous and endogenous arachidonate and that activation of the presynaptic muscarinic acetylcholine receptor increases the rate of prostaglandin E2 synthesis by inducing the release of tissue arachidonate from its phospholipid pools. The incorporation of radiolabeled arachidonate into tissue phospholipids is slow and Ca2+ independent. However, the electric organ slices readily oxidize the externally added, radiolabeled arachidonate via the cyclo-oxygenase pathway, with prostaglandin E2 being the major product (22 +/- 4% of the initial radioactivity).

Differential inhibition of the release of endogenous and newly synthesized acetylcholine from Torpedo synaptosomes by presynaptic muscarinic receptors.

Activation of Torpedo presynaptic muscarinic acetylcholine (ACh) receptors with the agonist oxotremorine (20 microM) results in the inhibition of Ca2+-dependent release of endogenous ACh from Torpedo synaptosomes. This effect is reversed by the muscarinic antagonist atropine (1 microM) which, by itself, has no effect. In contrast, under the same conditions the amount of newly synthesized radiolabeled [3H]ACh released is not affected by muscarinic ligands.