Forskolin blocks carbachol-mediated ion-permeability of chick myotube nicotinic receptors and inhibits binding of 3H-phencyclidine to Torpedo microsac nicotinic receptors.
Forskolin, a commonly used adenylate cyclase activator, was found to inhibit reversibly the carbachol-induced ion-translocating capacity of the nicotinic acetylcholine receptor (nAChR) on chick myotubes in a dose- (IC50 = 20 microM) and time-dependent manner. This effect was not correlated to increases in cellular cAMP. Forskolin, at a concentration (50 microM) that totally blocked the carbachol-induced 86Rb influx, caused no change in carbachol or alpha-bungarotoxin binding to chick myotube nAChR in situ. In contrast, in the presence of carbachol, forskolin inhibited (IC50 = 10 microM) the binding of 3H-phencyclidine, a putative nAChR ion-channel ligand, to Torpedo microsac nAChR. Inhibition of 3H-phencyclidine binding in the absence of carbachol was not complete. Membrane leakage studies on myotubes, measuring 3H-efflux from 2-deoxy-D(1-3H)-glucose loaded cells and electrophysiological measurements of membrane properties supported the interpretation that forskolin induced decreases in plasma membrane permeability. In conclusion, forskolin blocks the carbachol-mediated increase in permeability of the nAChR channel by (1) binding to the ion-channel (open state) and (2) generally perturbing the plasma membrane function possibly by interfering with the protein-lipid interface.
D000818:Animals; D002038:Bungarotoxins; D002217:Carbachol / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects; D002642:Chick Embryo; D002772:Cholera Toxin / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology*; D004996:Ethidium / Q000494:pharmacology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism*; D010622:Phencyclidine / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000187:drug effects*; D012414:Rubidium Radioisotopes; D014101:Torpedo
D002038:Bungarotoxins; D007473:Ion Channels; D011978:Receptors, Nicotinic; D012414:Rubidium Radioisotopes; D005576:Colforsin; D002217:Carbachol; D002772:Cholera Toxin; D004996:Ethidium; D010622:Phencyclidine