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Short‐ and long‐term differential effects of neuroprotective drug NS‐7 on voltage‐dependent sodium channels in adrenal chromaffin cells
Author(s) -
Yokoo Hiroki,
Shiraishi Seiji,
Kobayashi Hideyuki,
Yanagita Toshihiko,
Minami Shinichi,
Yamamoto Ryuichi,
Wada Akihiko
Publication year - 2000
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0703622
Subject(s) - veratridine , chromaffin cell , sodium channel , ouabain , cycloheximide , chemistry , adrenal medulla , pharmacology , biology , sodium , endocrinology , microbiology and biotechnology , medicine , catecholamine , biochemistry , protein biosynthesis , organic chemistry
In cultured bovine adrenal chromaffin cells, NS‐7 [4‐(4‐fluorophenyl)‐2‐methyl‐6‐(5‐piperidinopentyloxy) pyrimidine hydrochloride], a newly‐synthesized neuroprotective drug, inhibited veratridine‐induced 22 Na + influx via voltage‐dependent Na + channels (IC 50 =11.4 μ M ). The inhibition by NS‐7 occurred in the presence of ouabain, an inhibitor of Na + ,K + ATPase, but disappeared at higher concentration of veratridine, and upon the washout of NS‐7. NS‐7 attenuated veratridine‐induced 45 Ca 2+ influx via voltage‐dependent Ca 2+ channels (IC 50 =20.0 μ M ) and catecholamine secretion (IC 50 =25.8 μ M ). Chronic (12 h) treatment of cells with NS‐7 increased cell surface [ 3 H]‐STX binding by 86% (EC 50 =10.5 μ M ; t 1/2 =27 h), but did not alter the K D value; it was prevented by cycloheximide, an inhibitor of protein synthesis, or brefeldin A, an inhibitor of vesicular transport from the trans ‐Golgi network, but was not associated with increased levels of Na + channel α‐ and β 1 ‐subunit mRNAs. In cells subjected to chronic NS‐7 treatment, 22 Na + influx caused by veratridine (site 2 toxin), α‐scorpion venom (site 3 toxin) or β‐scorpion venom (site 4 toxin) was suppressed even after the extensive washout of NS‐7, and veratridine‐induced 22 Na + influx remained depressed even at higher concentration of veratridine; however, either α‐ or β‐scorpion venom, or Ptychodiscus brevis toxin‐3 (site 5 toxin) enhanced veratridine‐induced 22 Na + influx as in nontreated cells. These results suggest that in the acute treatment, NS‐7 binds to the site 2 and reversibly inhibits Na + channels, thereby reducing Ca 2+ channel gating and catecholamine secretion. Chronic treatment with NS‐7 up‐regulates cell surface Na + channels via translational and externalization events, but persistently inhibits Na + channel gating without impairing the cooperative interaction between the functional domains of Na + channels.British Journal of Pharmacology (2000) 131 , 779–787; doi: 10.1038/sj.bjp.0703622