thapsigargin and epibatidine

Nonylphenol (NP) is the most critical metabolite of alkylphenol polyethoxylate detergents. NP is known as an endocrine disruptor with estrogenic activities and as an inhibitor of endoplasmic reticulum Ca(2+)-ATPase. Estrogen has modulatory roles on ligand-gated ion channels, such as nicotinic acetylcholine receptors (nAChRs). Ca(2+)-ATPase inhibitors can modulate the cytosolic calcium concentration ([Ca(2+)](c)]) and thus can affect the calcium signaling coupled with nAChRs. Therefore, NP is predicted to have complex effects on the Ca(2+) signaling and secretion coupled with nAChRs. This study investigated these effects using bovine adrenal chromaffin cells. The results show that NP suppressed the Ca(2+) signaling coupled with nAChRs and voltage-operated Ca(2+) channels in a dose-dependent manner, with IC(50)s of 1 and 5.9 microM, respectively. Estradiol exhibits similar suppression but much lower inhibitory potencies. NP alone induced a transient rise in [Ca(2+)](c) in the presence or absence of extracellular calcium. Thapsigargin, an endoplasmic reticulum Ca(2+)-ATPase inhibitor, partially suppressed the [Ca(2+)](c) rise induced by NP, but NP totally blocked the [Ca(2+)](c) rise induced by thapsigargin. This illustrates that NP can cause Ca(2+) release from thapsigargin-insensitive pools. Thapsigargin suppressed the Ca(2+) signaling coupled with nAChRs but increased that coupled with voltage-operated Ca(2+) channels. We propose that three routes are responsible for the effects of NP on nAChRs: named receptor channels, voltage-gated Ca(2+) channels, and Ca(2+)-induced Ca(2+) release. Three routes are related to the characteristics of NP as steroid-like compounds and Ca(2+)-ATPase inhibitor.

Topics: Adrenal Medulla; Animals; Bridged Bicyclo Compounds, Heterocyclic; Calcium; Calcium Channels; Calcium Signaling; Calcium-Transporting ATPases; Carbachol; Catecholamines; Cattle; Cells, Cultured; Chromaffin Cells; Chromatography, High Pressure Liquid; Dimethylphenylpiperazinium Iodide; Dose-Response Relationship, Drug; Epinephrine; Estradiol; Membrane Potentials; Norepinephrine; Phenols; Potassium Chloride; Pyridines; Receptors, Nicotinic; Sarcoplasmic Reticulum Calcium-Transporting ATPases; Thapsigargin

The mechanisms of TDI (2,4-toluene diisocyanate)-induced occupational asthma are not fully established. Previous studies have indicated that TDI induces non-specific bronchial hyperreactivity to methacholine and induces contraction of smooth muscle tissue by activating 'capsaicin-sensitive' nerves resulting asthma. Cytosolic-free calcium ion concentrations ([Ca(2+)](c)) are elevated when either capsaicin acts at vanilloid receptors, or methacholine at muscarinic receptors. This study therefore investigated the effects of TDI on Ca(2+) mobilization in human neuroblastoma SH-SY5Y cells. TDI was found to elevate [Ca(2+)](c) by releasing Ca(2+) from the intracellular stores and extracellular Ca(2+) influx. 500 microM TDI induced a net [Ca(2+)](c) increase of 112+/-8 and 78+/-6 nM in the presence and absence of extracellular Ca(2+), respectively. In Ca(2+)-free buffer, TDI induced Ca(2+) release from internal stores to reduce their Ca(2+) content and this reduction was evidenced by a suppression occurring on the [Ca(2+)](c) rise induced by thapsigargin, ionomycin, and methacholine after TDI incubation. In the presence of extracellular Ca(2+), simultaneous exposure to TDI and methacholine led a higher level of [Ca(2+)](c) compared to single methacholine stimulation, that might explain that TDI induces bronchial hyperreactivity to methacholine. We conclude that TDI is capable of interfering the [Ca(2+)](c) homeostasis including releasing Ca(2+) from internal stores and inducing extracellular Ca(2+) influx. The interaction of this novel character and bronchial hyperreactivity need further investigation.

Topics: Atropine; Bridged Bicyclo Compounds, Heterocyclic; Calcium; Calcium Signaling; Cell Line, Tumor; Cytosol; Dose-Response Relationship, Drug; Drug Synergism; Egtazic Acid; Endoplasmic Reticulum; Hexamethonium; Homeostasis; Humans; Intracellular Fluid; Ionomycin; Methacholine Chloride; Neuroblastoma; Potassium; Pyridines; Receptor, Muscarinic M3; Thapsigargin; Toluene 2,4-Diisocyanate; Verapamil