Steviol glycosides (SGs), such as stevioside and rebaudioside A, are natural, non-caloric sweet-tasting organic molecules, present in extracts of the scrub plant Stevia rebaudiana, which are widely used as sweeteners in consumer foods and beverages. TRPM5 is a Ca2+-activated cation channel expressed in type II taste receptor cells and pancreatic β-cells. Here we show that stevioside, rebaudioside A and their aglycon steviol potentiate the activity of TRPM5. We find that SGs potentiate perception of bitter, sweet and umami taste, and enhance glucose-induced insulin secretion in a Trpm5-dependent manner. Daily consumption of stevioside prevents development of high-fat-diet-induced diabetic hyperglycaemia in wild-type mice, but not in Trpm5−/− mice. These results elucidate a molecular mechanism of action of SGs and identify TRPM5 as a potential target to prevent and treat type 2 diabetes.

Voltage-gated sodium channels are essential for the propagation of action potentials in nociceptive neurons.

Gambierol is a marine polycyclic ether toxin belonging to the group of ciguatera toxins. It does not activate voltage-gated sodium channels (VGSCs) but inhibits Kv1 potassium channels by an unknown mechanism. While testing whether Kv2, Kv3, and Kv4 channels also serve as targets, we found that Kv3.1 was inhibited with an IC 50 of 1.2 ؎ 0.2 nM, whereas Kv2 and Kv4 channels were insensitive to 1 M gambierol. Onset of block was similar from either side of the membrane, and gambierol did not compete with internal cavity blockers. The inhibition did not require channel opening and could not be reversed by strong depolarization. Using chimeric Kv3.1-Kv2.1 constructs, the toxin sensitivity was traced to S6, in which T427 was identified as a key determinant. In Kv3.1 homology models, T427 and other molecular determinants (L348, F351) reside in a space between S5 and S6 outside the permeation pathway. In conclusion, we propose that gambierol acts as a gating modifier that binds to the lipid-exposed surface of the pore domain, thereby stabilizing the closed state. This site may be the topological equivalent of the neurotoxin site 5 of VGSCs. Further elucidation of this previously undescribed binding site may explain why most ciguatoxins activate VGSCs, whereas others inhibit voltage-dependent potassium (Kv) channels. This previously undescribed Kv neurotoxin site may have wide implications not only for our understanding of channel function at the molecular level but for future development of drugs to alleviate ciguatera poisoning or to modulate electrical excitability in general.ciguatera ͉ neurotoxin site 5 ͉ polycyclic ether toxin ͉ potassium channels ͉ Kv3.1

Eudra CT: 2014-001499-73; 31/7/2014.

In this study, we pharmacologically characterized gambierol, a marine polycyclic ether toxin which is produced by the dinoflagellate Gambierdiscus toxicus.

Cnidarian envenomations cause a burning-pain sensation of which the underlying mechanisms are unknown. Activation of TRPV1, a non-selective cation channel expressed in nociceptive neurons, leads to cell depolarisation and pain. Here, we show in vitro and in vivo evidence for desensitization-dependent TRPV1 activation in cnidarian envenomations. Cnidarian venom induced a nociceptive reactivity, comparable to capsaicin, in laboratory rats, which could be reduced by the selective TRPV1 antagonist, BCTC. These findings are the first to explain at least part of the symptomology of cnidarian envenomations and provide insights into the design of more effective treatments for this global public health problem.

In this study, we isolated and pharmacologically characterized the first a-like toxin from the venom of the scarcely studied Iranian scorpion Odonthobuthus doriae. The toxin was termed OD1 and its primary sequence was determined: GVRDA-YIADDKNCVYTCASNGYCNTECTKNGAESGYCQWIGR-YGNACWCIKLPDEVPIRIPGKCR. Using the two-electrode voltage clamp technique, the pharmacological effects of OD1 were studied on three cloned voltage-gated Na + channels expressed in Xenopus laevis oocytes (Na v 1.2/b 1 , Na v 1.5/b 1 , para/tipE). The inactivation process of the insect channel, para/tipE, was severely hampered by 200 nM of OD1 (EC 50 = 80 ± 14 nM) while Na v 1.2/ b 1 still was not affected at concentrations up to 5 lM. Na v 1.5/b 1 was influenced at micromolar concentrations.

Today, hair testing is considered to be the standard method for the detection of chronic drug abuse. Nevertheless, the differentiation between systemic exposure and external contamination remains a major challenge in the forensic interpretation of hair analysis. Nowadays, it is still impossible to directly show the difference between external contamination and use-related incorporation. Although the effects of washing procedures on the distribution of (incorporated) drugs in hair remain unknown, these decontamination procedures prior to hair analysis are considered to be indispensable in order to exclude external contamination. However, insights into the effect of decontamination protocols on levels and distribution of drugs incorporated in hair are essential to draw the correct forensic conclusions from hair analysis; we studied the consequences of these procedures on the spatial distribution of cocaine in hair using imaging mass spectrometry. Additionally, using metal-assisted secondary ion mass spectrometry, we are the first to directly show the difference between cocaine-contaminated and user hair without any prior washing procedure.