Up-regulation of functional voltage-dependent sodium channels by insulin in cultured bovine adrenal chromaffin cells.
Treatment of cultured bovine adrenal chromaffin cells with 100 nM insulin raised [3H]saxitoxin ([3H]-STX) binding in a time-dependent manner (t1/2 = 26 h). Insulin (100 nM for 4 days) increased the Bmax of [3H]STX binding by 49% without changing the KD value and also augmented the maximal influx of 22Na+ due to 560 microM veratridine by 39% without altering the EC50 value of veratridine. The stimulatory effect of insulin on 22Na+ influx was concentration-dependent with an EC50 of 3 nM, whereas insulin-like growth factor (IGF)-I had little effect at 1 nM. Ptychodiscus brevis toxin-3 allosterically potentiated veratridine (100 microM)-induced 22Na+ influx by approximately twofold in both insulin-treated cells and untreated cells. Veratridine-induced 45Ca2+ influx via voltage-dependent Ca2+ channels and catecholamine secretion were also enhanced by insulin treatment, whereas insulin did not alter nicotine-induced 22Na+ influx via the nicotinic receptor-ion channel complex and high-K+ (direct activation of voltage-dependent Ca2+ channels)-induced 45Ca2+ influx. Stimulatory effects of insulin on [3H]-STX binding and veratridine-induced 22Na+ influx were nullified by simultaneous treatment with either 5,6-dichlorobenzimidazole riboside, an inhibitor of RNA synthesis, or cycloheximide, an inhibitor of protein synthesis, whereas insulin treatment did not appreciably increase the level of mRNA encoding the Na+ channel alpha-subunit. These results suggest that the binding of insulin to insulin (but not IGF-I) receptors mediates the up-regulation of functional Na+ channel expression at plasma membranes; this up-regulation may be due, at least in part, to the de novo synthesis of an as yet unidentified protein(s).
Yamamoto
R
R
Department of Pharmacology, Miyazaki Medical College, Japan.
Yanagita
T
T
Kobayashi
H
H
Yuhi
T
T
Yokoo
H
H
Wada
A
A
D000313:Adrenal Medulla / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000187:drug effects / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D004004:Dichlororibofuranosylbenzimidazole / Q000494:pharmacology; D004141:Dinoflagellida; D004357:Drug Synergism; D004594:Electrophysiology; D004837:Epinephrine / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D007700:Kinetics; D008387:Marine Toxins / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D035964:Oxocins; D011972:Receptor, Insulin / Q000502:physiology; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000502:physiology; D012530:Saxitoxin / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000096:biosynthesis* / Q000502:physiology; D014158:Transcription, Genetic / Q000187:drug effects*; D015854:Up-Regulation; D014701:Veratridine / Q000494:pharmacology; D000095702:Polyether Toxins
D003513:Cycloheximide; D004004:Dichlororibofuranosylbenzimidazole; D004837:Epinephrine; D007328:Insulin; D007334:Insulin-Like Growth Factor I; D008387:Marine Toxins; D009638:Norepinephrine; D010042:Ouabain; D035964:Oxocins; D011972:Receptor, Insulin; D011978:Receptors, Nicotinic; D012530:Saxitoxin; D012964:Sodium; D015222:Sodium Channels; D014701:Veratridine; C041017:brevetoxin T17; D000095702:Polyether Toxins