The Anti-Botulism Triterpenoid Toosendanin Elicits Calcium Increase and Exocytosis in Rat Sensory Neurons

Abstract

Toosendanin, a triterpenoid from Melia toosendan Sieb et Zucc, has been found before to be an effective anti-botulism agent, with a bi-phasic effect at both motor nerve endings and central synapse: an initial facilitation followed by prolonged depression. Initial facilitation may be due to activation of voltage-dependent calcium channels plus inhibition of potassium channels, but the depression is not fully understood. Toosendanin has no effect on intracellular calcium or secretion in the non-excitable pancreatic acinar cells, ruling out general toosendanin inhibition of exocytosis. In this study, toosendanin effects on sensory neurons isolated from rat nodose ganglia were investigated. It was found that toosendanin stimulated increases in cytosolic calcium and neuronal exocytosis dose dependently. Experiments with membrane potential indicator bis-(1,3-dibutylbarbituric acid)trimethine oxonol found that toosendanin hyperpolarized capsaicin-insensitive but depolarized capsaicinsensitive neurons; high potassium-induced calcium increase was much smaller in hyperpolarizing neurons than in depolarizing neurons, whereas no difference was found for potassium-induced depolarization in these two types of neurons. In neurons showing spontaneous calcium oscillations, toosendanin increased the oscillatory amplitude but not frequency. Toosendanin-induced calcium increase was decreased in calcium-free buffer, by nifedipine, and by transient receptor potential vanilloid 1 (TRPV1) antagonist capsazepine. Simultaneous measurements of cytosolic and endoplasmic reticulum (ER) calcium showed an increase in cytosolic but a decrease in ER calcium, indicating that toosendanin triggered ER calcium release. These data together indicate that toosendanin modulates sensory neurons, but had opposite effects on membrane potential depending on the presence or absence of capsaicin receptor/TRPV 1 channel.

Extracellular Histones Activate Plasma Membrane Toll-Like Receptor 9 to Trigger Calcium Oscillations in Rat Pancreatic Acinar Tumor Cell AR4-2J

“…The minimum effective histone concentration was found to be 2 mgL −1 (b); higher concentrations (5, 20 mgL −1 ) (c,d) induced progressively stronger calcium oscillations (Figure 3A–E). Note the varied resting F 340 /F 380 ratio levels among different cells, which have also been noted before, and are normalized when performing data analysis [46,47,49]. Integrated calcium responses were plotted against histone concentrations for each histone (H1, H2A, H2B, H3, and H4) and are presented in both bar charts and line curves (Figure 3Fa,Fb).…”

“…Fluorescent calcium imaging was done as reported previously [6,44,47,48] in a Photon Technology International (PTI, Ediosn, N.J., USA) calcium measurement system, with a photon-counting PMT (PTI PMT814) or a CCD (NEO-5.5-CL-3, Andor) as detector, in an inverted fluorescent microscope (Olympus IX or Nikon NE 300), with fluorescence collected at 510 ± 25 nm. The fluorescent ratios of F 340 /F 380 were shown as indications of calcium concentrations and were plotted against time with SigmaPlot as before [6,47,49].…”

NanoLuc Bioluminescence-Driven Photodynamic Activation of Cholecystokinin 1 Receptor with Genetically-Encoded Protein Photosensitizer MiniSOG

“…Cytosolic calcium was measured in an inverted fluorescent microscope (Nikon TE-2000U) coupled to a PTI (Photon Technology International Inc., now HORIBA, Edison, NJ, USA) calcium measurement system with alternating excitations of the loaded Fura-2 at 340 nm/380 nm (DeltaRam X), and emitted Fura-2 fluorescence (dichroic mirror 400DCLP, emitter 510 ± 40 nm) was detected with a charge-coupled device (CCD) camera (NEO-5.5-CL-3, Andor/Oxford Instruments, UK). Calcium concentration was expressed as F 340 /F 380 ratios and plotted against time with SigmaPlot, as reported before [1,2,28,31,33,52,53]. In the figures shown in Results, the original colored calcium tracings were each from individual cells and only representative tracings from 1 out of N (as indicated, N ≥ 3) identical experiments were presented.…”

Natural products: a hope for glioblastoma patients

“…Toosendanin (TSN) is a triterpenoid saponin isolated from the Chinese herb Melia toosendan and is known to inhibit acetylcholine release at the nerve terminals. Though used as a pesticide, recent studies have shown its anti-proliferative effect against lymphoma, leukemia and hepatocellular cancer cell lines [ 225 – 228 ]. In addition, TSN also inhibits proliferation of U87 and C6 cell line at nanomolar (10 nM) concentrations [ 229 ].…”