Effect of lanthanum ions on the release of acetylcholine induced by tityustoxin, K+ and ouabain from myenteric plexus and brain cortical slices

Isotopic tracer studies of chemical behavior of rare earth elements in environmental and biological sciences

Rare earth elements (REE), a group of elements with atomic numbers from 57 to 71, have been widely applied in recent years not only in industry but also in agriculture, forestry, animal husbandry and medicine. Numerous anthropogenic activities make REE to easily enter the environment and finally the human body via the food chain. Therefore, detailed studies on chemical behavior of these metals in environmental and biological systems are imperative. Isotopic tracer method is especially suited to such studies and has played an important role in assessing the environmental effects of REE. In this paper, some recent progress in the study of chemical behavior of REE in environmental and biological sciences made by the isotopic tracer method is outlined.

Investigation of the effect of PhTx2, from the venom of the spider Phoneutria nigriventer, on the release of [3H]-acetylcholine from rat cerebrocortical synaptosomes

Venoms from spiders are an important source of toxins that can help on the dissection of mechanisms involved in neurotransmission. Among them is the venom of the spider Phoneutria nigriventer that contains several toxic fractions with different targets in mammals and/or insects. We here report that one of these fractions (PhTx2) is able to evoke acetylcholine release from rat cortical synaptosomes and that this effect is dependent on extracellular calcium and is inhibited by the sodium channel blocker tetrodotoxin.

Inhibition of potassium-stimulated acetylcholine release from rat brain cortical slices by two high-affinity analogs of vesamicol

In this work, we investigated the effects of two structural analogs of the drug vesamicol, which inhibits the vesicular acetylcholine (ACh) transport, on the potassium-stimulated release of ACh from rat brain cortical slices. These vesamicol analogs, 4-aminobenzovesamicol (ABV) and (trans)-cyclohexovesamicol (transDec), were almost as potent as vesamicol in inhibiting the evoked release of ACh from cortex slices. Similar to vesamicol, the presence of these analogues inhibited the ability of ACh newly-synthesized from [3H]choline to become releasable. However, vesamicol's action was reversible, while ABV and transDec caused a persistent block of this [3H]ACh release. In addition, vesamicol did not affect the release of pre-stored [3H]ACh, but ABV and transDec partially inhibited the release of [3H]ACh in this condition, suggesting that the two latter drugs may alter some of the steps posterior to the entry of [3H]ACh into synaptic vesicles. The rank order of potency for these drugs to reduce ACh release (vesamicol = transDec > ABV) is close to the rank order for inhibition of ACh vesicular transport (transDec > vesamicol > ABV), but is completely different from the order of affinities of these drugs for the vesamicol receptor (ABV > transDec > > vesamicol). These results suggest that although these two vesamicol analogs are able to block ACh release due to their effects on the vesicular transport system, they may have other unexpected actions not shared by vesamicol.

The effect of PhTx3 on the release of 3H-acetylcholine induced by tityustoxin and potassium in brain cortical slices and myenteric plexus

The venom of the Brazilian spider Phoneutria nigriventer possesses several neurotoxic polypeptidic fractions. Previous work has established that one of the toxic components, PhTx3, inhibited Ca(2+)-dependent glutamate release and the increase in cytosolic free Ca2+ in response to membrane depolarization. In the present work, we investigated the effect of PhTx3 on the release of acetylcholine (ACh) from brain and peripheral neurons. PhTx3 decreased the release of [3H]-ACh induced by tityustoxin and KCl in brain cortical slices and myenteric plexus. The inhibitory effect of myenteric plexus had the same magnitude as that obtained in the absence of extracellular Ca2+. However, in brain PhTx3 was less efficient at decreasing the evoked release of ACh. These experiments suggest that the target of PhTx3 is coupled to the process of release of ACh in brain and autonomic nervous system.