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Modulation of the Nicotinic Acetylcholine Receptor by Dioscorine in Clonal Rat Phaeochlomocytoma (PC12) Cells

https://doi.org/10.1006/pest.1999.2423Get rights and content

Abstract

Dioscorine is a toxin isolated from the tubers of tropical yam, Dioscorea hispida Schlussel that has insecticidal and antifeedant activities. The effects of dioscorine on the neuronal nicotinic acetylcholine receptor in rat clonal phaeochlomocytoma (PC12) cells were studied using whole-cell and single-channel patch clamp techniques. Dioscorine at concentrations of 0.45–450 μMM accelerated the desensitization of current induced by 100 μMM acetylcholine and suppressed the current in a dose-dependent manner. Dioscorine itself did not induce any current at concentrations ranging from 0.45 to 450 μMM. At the single-channel level, 4.5–450 μMM dioscorine, when co-applied with 10 μMM acetylcholine, markedly shortened the open time and caused bursts to appear in a dose-dependent manner. The mean open time, mean closed time, and burst duration were decreased by dioscorine. These changes of single-channel kinetics result in a significant decrease in the total charge carried through the open channels, explaining the suppressive effect of dioscorine on acetylcholine-induced whole-cell currents. The suppressive effect of dioscorine on the acetylcholine-induced current is suggested to play an important role in the toxic actions in animals.

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    This work was supported by NIH Grant NS14143 and Grant-in-Aid for Developmental Scientific Research 07406003, by Ministry of Education, Science and Culture of Japan 07556014, and by the University of Tsukuba Research Projects. The authors thank Drs. Edson X. Albuquerque and Edna F. R. Pereira of the University of Maryland School of Medicine for providing the PC12 cell line, Nayla Hasan for technical assistance, and Julia Irizarry, Yukiko Sato, and Tokiko Tamaoki for secretarial assistance.

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