Effects of Tobacco Cembranoid 4S, 6R-Cembratrienediol on Nicotinic Acetylcholine Receptors in PC12 Cells
Nery, A.A.1; Szeto, A.C.2; Eterovic, V.A.2*; and Ulrich, H.1*
1Department of Biochemistry, Instituto de Química, Universidade de São Paulo, São Paulo, Brazil
2Department of Biochemistry, Universidad Central del Caribe, Bayamon, Puerto Rico *Corresponding authors
Tobacco cembranoids are cyclic diterpenoids shown to modulate agonist-induced currents of nicotinic receptors in a reversible, noncompetitive manner (Ferchmin et al. 2001, J Neurosci Res, 64:18-25, Eaton et al. 2004, Neurosci Lett, 366:94-102). There is also evidence that tobacco cembranoids can confer neuroprotection of NMDA-induced excitotoxitiy in acute hippocampal slices (Ferchmin et al. 2005, J Neurosci Res, 82:631-641). In this study, we examine the effects of 4S, 6R-cembratriene 4,6 diol (4S) on carbamylcholine (CCh)-induced whole-cell currents in neuronal-differentiated PC12 cells. Whole-cell recordings of CCh-induced currents were obtained in the presence and absence of various concentrations of 4S. A wide variety of desensitization rates, indicative of heterogeneity of nAChRs formed by alpha-3, 5, 7 and beta 2, 4 subunits, were observed in the absence of 4S. The addition of 4S in the presence of CCh inhibited fast-desensitizing receptors (desensitization constant <90 ms, apparent Ki in the low micromolar range) more potently than slow-desensitizing receptors (desensitization constant >250 ms, apparent Kd > 0.1 mM). Since alpha7 homomeric nAChRs are the fastest-desensitizing nAChRs in these cells, the results are indicative that the 4S cembranoid preferentially inhibits the alpha-7 receptor in differentiated PC12 cells.
Supported by NINDS and NCRR SNRP (Grant no. NS39408) to V.A.E. and
FAPESP (Grant No. 01/08827-4), and CNPq to H.U.
|