Up‐Regulation of Functional Voltage‐Dependent Sodium Channels by Insulin in Cultured Bovine Adrenal Chromaffin Cells

Abstract

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 µM 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 µM)‐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 α‐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).

New Twist on Neuronal Insulin Receptor Signaling in Health, Disease, and Therapeutics

“…In auditory and visual circuits in brain, axonal conduction velocity was decreased in streptozotocin-induced diabetic rats; insulin treatment with its subcutaneous implants, initiated 6 months after streptozotocin-induced diabetes mellitus, almost completely reversed the existing abnormalities in brain, whereas normalization of blood glucose levels had no effect (10). Because Na + channel is essential to generation and conduction of action potential, up-regulation of cell surface Na + channel by insulin demonstrated in our study (28) may be instructive in understanding the regenerative effect of insulin in diabetic neuropathy. More surprisingly, the axon guidance role of insulin receptor was evidenced by Song et al (84) in the photoreceptor of the fruit fly Drosophila; insulin receptor signaling was required for the extending neuronal axon to find its way from the retina to the brain during development of visual system.…”

Differential Effects of Short and Prolonged Exposure to Carvedilol on Voltage-Dependent Na+Channels in Cultured Bovine Adrenal Medullary Cells

“…A simple interpretation of these results is that carvedilol may stimulate the translational or posttranslational step(s) of Na ϩ channel synthesis or may inhibit the internalization/degradation of Na ϩ channels. Yamamoto et al (1996) also observed that treatment of cultured adrenal medullary cells with insulin up-regulates the functional Na ϩ channels without causing any change in the level of mRNA encoding the Na ϩ channel ␣-subunit. In the present study, brefeldin A, an inhibitor of vesicle-mediated externalization of newly synthesized proteins from the trans-Golgi network, abolished the up-regulation of Na ϩ channels by carvedilol (Fig.…”

Destabilization of Nav1.7 Sodium Channel α-Subunit mRNA by Constitutive Phosphorylation of Extracellular Signal-Regulated Kinase: Negative Regulation of Steady-State Level of Cell Surface Functional Sodium Channels in Adrenal Chromaffin Cells

“…22 Na ϩ influx was measured by incubating the cells with 2 Ci 22 NaCl at 37°C for 5 min in 1 ml of KRP buffer in the absence or presence of veratridine, ouabain, PbTx-3, and nicotine. The cells were washed with ice-cold KRP buffer, solubilized in 10% Triton X-100, and counted for radioactivity (Wada et al, 1986(Wada et al, , 1992Yamamoto et al, 1996Yamamoto et al, , 1997Yanagita et al, 1996;Yuhi et al, 1996;Shiraishi et al, 2001a,b).…”