Vol. 287, Issue 2, 441-447, November 1998

Carbamazepine-Induced Up-regulation of Voltage-dependent Na⁺ Channels in Bovine Adrenal Medullary Cells in Culture

Reiji Yoshimura, Nobuyuki Yanagihara, Takeshi Terao, Yasuhito Uezono, Yumiko Toyohira, Susumu Ueno, Kazuhiko Abe and Futoshi Izumi

Department of Psychiatry (R.Y., T.T., K.A.) and Department of Pharmacology (N.Y., Y.U., Y.T., S.U., F.I.), University of Occupational and Environmental Health, School of Medicine, Kitakyushu, Japan

Treatment of cultured bovine adrenal medullary cells with carbamazepine (CBZ) for 5 days caused an increase in catecholamine secretion induced by veratridine, an activator of voltage-dependent Na⁺ channels. However, no increase was stimulated by carbachol, an agonist of nicotinic receptors, or by 56 mM K⁺, a depolarizing agent that activates voltage-dependent Ca⁺⁺ channels. CBZ (30 µg/ml) treatment enhanced veratridine-induced catecholamine secretion in a time-dependent manner (increases of 25%, 65% and 70% for 3, 5 and 7 days of treatment, respectively). CBZ treatment (5 days) increased veratridine-induced catecholamine secretion in a concentration-dependent manner (increases of 27%, 36%, 45% and 55% at 10, 15, 20 and 30 µg/ml of CBZ, respectively). CBZ treatment also increased ²²Na⁺ influx and ⁴⁵Ca⁺⁺ influx stimulated by veratridine. The stimulatory effect of CBZ treatment on catecholamine secretion was blocked by either actinomycin D or cycloheximide, an inhibitor of protein synthesis. Additive responses of catecholamine secretion and ²²Na⁺ influx induced by veratridine were associated with combined exposure of the cells to CBZ and dibutyryl cyclic AMP. CBZ treatment (30 µg/ml, 5 days) significantly increased the specific binding of [³H]saxitoxin to cell membranes. A Scatchard analysis of [³H]saxitoxin binding revealed that CBZ increased the B_max value without any change in the dissociation constant. These findings suggest that CBZ up-regulates the density and activity of voltage-dependent Na⁺ channels.