TY - JOUR T1 - Up-Regulation of Cell Surface Sodium Channels by Cyclosporin A, FK506, and Rapamycin in Adrenal Chromaffin Cells JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 657 LP - 665 VL - 297 IS - 2 AU - Seiji Shiraishi AU - Toshihiko Yanagita AU - Hideyuki Kobayashi AU - Yasuhito Uezono AU - Hiroki Yokoo AU - Shin-Ichi Minami AU - Mayumi Takasaki AU - Akihiko Wada Y1 - 2001/05/01 UR - http://jpet.aspetjournals.org/content/297/2/657.abstract N2 - Treatment of cultured bovine adrenal chromaffin cells with cyclosporin A (CsA) increased cell surface [3H]saxitoxin ([3H]STX) binding by 56% in a time (t 1/2 = 15.2 h)- and concentration (EC50 = 2.9 μM)-dependent manner but did not change the K d value. In CsA-treated cells, veratridine-induced 22Na+ influx was augmented with no change in the EC50 of veratridine; also, α- and β-scorpion venom and Ptychodiscus brevis toxin-3 enhanced veratridine-induced 22Na+ influx in a more than additive manner, as in nontreated cells. CsA treatment for 1 to 24 h inhibited calcineurin activity, measured by the in vitro assay, with the IC50 of 0.6 μM but did not alter cellular level of calcineurin. FK506 or rapamycin elevated [3H]STX binding by 36 or 25%, whereas GPI-1046, an immunophilin ligand incapable to inhibit calcineurin, or okadaic acid, an inhibitor of protein phosphatases 1 and 2A, had no increasing effect. The rise of [3H]STX binding by CsA was attenuated by the coincident treatment with brefeldin A (BFA), an inhibitor of vesicular exit from the trans-Golgi network. The internalization rate of cell surface Na+ channels, as determined in the presence of BFA, was decreased in CsA (but not rapamycin)-treated cells (t 1/2 = 20.3 h), compared with nontreated cells (t 1/2 = 13.7 h). CsA treatment, however, did not elevate cellular levels of Na+ channel α-subunit and Na+ channel α- and β1-subunit mRNAs. In CsA-treated cells, veratridine-induced 45Ca2+ influx via voltage-dependent Ca2+ channels and catecholamine secretion were enhanced, whereas high K+-induced45Ca+ influx was not. Thus, the inhibition of calcineurin or rapamycin-binding protein causes up-regulation of cell surface functional Na+ channels via modulating externalization and internalization of Na+ channels, thus enhancing Ca2+ channel gating and catecholamine secretion. The American Society for Pharmacology and Experimental Therapeutics ER -