Distribution of I, II and III subtypes of voltage-sensitive Na+ channel mRNA in the rat brain

The α subunit of voltage-gated Na+ channels of brain, skeletal muscle, and cardiomyocytes is functionally modulated by the accessory β1, but not the β2 subunit. In the present study, we used β1/β2 chimeras to identify molecular regions within the β1 subunit that are responsible for both the increase of the current density and the acceleration of recovery from inactivation of the human heart Na+ channel (hH1). The channels were expressed in Xenopus oocytes. As a control, we coexpressed the β1/β2 chimeras with rat brain IIA channels. In agreement with previous studies, the β1 extracellular domain sufficed to modulate IIA channel function. In contrast to this, the extracellular domain of the β1 subunit alone was ineffective to modulate hH1. Instead, the putative membrane anchor plus either the intracellular or the extracellular domain of the β1 subunit was required. An exchange of the β1 membrane anchor by the corresponding β2 subunit region almost completely abolished the effects of the β1 subunit on hH1, suggesting that the β1 membrane anchor plays a crucial role for the modulation of the cardiac Na+ channel isoform. It is concluded that the β1 subunit modulates the cardiac and the neuronal channel isoforms by different molecular interactions: hH1 channels via the membrane anchor plus additional intracellular or extracellular regions, and IIA channels via the extracellular region only.

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Efficient expression of rat brain type IIA Na+ channel α subunits in a somatic cell line

Neuron ◽

10.1016/0896-6273(92)90108-p ◽

1992 ◽

Vol 8 (1) ◽

pp. 59-70 ◽

Cited By ~ 83

Author(s):

James W. West ◽

Todd Scheuer ◽

Laurie Maechler ◽

William A. Catterall

Keyword(s):

Somatic Cell ◽

Rat Brain ◽

Cell Line ◽

Na Channel ◽

Efficient Expression ◽

Α Subunits

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123 Localization of B1 subunit of voltage sensitive Na+ channel mRNA in the rat brain

Neuroscience Research Supplements ◽

10.1016/s0921-8696(05)80735-2 ◽

1993 ◽

Vol 18 ◽

pp. S24

Author(s):

Tatsuo Furuyama ◽

Yoshiko Iwahashi ◽

Shinobu Inagaki ◽

Hiroshi Takagi

Keyword(s):

Rat Brain ◽

Na Channel

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Relationship between energy expenditure and ion channel density in the turtle and rat brain

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1989.257.6.r1354 ◽

1989 ◽

Vol 257 (6) ◽

pp. R1354-R1358 ◽

Cited By ~ 4

Author(s):

R. A. Edwards ◽

P. L. Lutz ◽

D. G. Baden

Keyword(s):

Energy Consumption ◽

Energy Expenditure ◽

Ion Channel ◽

Rat Brain ◽

Receptor Interaction ◽

Na Channel ◽

Apparent Difference ◽

Na Channels ◽

Channel Density ◽

Rat Synaptosomes

Synaptosomes were isolated from turtle and rat brains to determine whether differences in brain ion channel densities accounted for the turtle's ability to survive anoxia compared with the mammal. The Na(+)-channel binding neurotoxin brevetoxin showed high-affinity specific binding in both turtle and rat synaptosomes, suggesting specific ligand-receptor interaction. The maximum binding capacity (Bmax) value for the turtle was only about one-third of that found for the rat synaptosomes, suggesting that the turtle synaptosome has a correspondingly lower Na+ channel density than the rat. This apparent difference in Na+ channel density is not reflected in metabolic rates, since at the same temperature (31 degrees C) the O2 consumption of both the rat and turtle synaptosome was almost identical. The large reductions in energy expenditure seen in synaptosomes incubated in Na(+)-free media and in media containing ouabain (approximately 50% turtle, 80% rat) are probably related to the halting of transmembrane Na(+)-K+ exchange. The greater reduction in the rat may be related to the apparent greater density of Na+ channels in the rat brain. However, compared with the 90% reduction in brain metabolism that occurs when the turtle brain becomes anoxic, the differences in ion channel density and in the costs of ion pumping between the rat and turtle brain are trivial. Closing Na+ channels with tetrodotoxin and increasing Na+ channel activation with veratridine caused substantial decreases and increases in synaptosome energy consumption, respectively. This suggests that the modulation of ion channel conductance has a significant effect on metabolic cost and may be an important mechanism to reduce energy consumption and electrical activity in the anoxic turtle brain, while still maintaining ionic gradients.

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Characterization of endogenous sodium channel gene expressed in Chinese hamster ovary cells

AJP Cell Physiology ◽

10.1152/ajpcell.1993.264.4.c803 ◽

1993 ◽

Vol 264 (4) ◽

pp. C803-C809 ◽

Cited By ~ 19

Author(s):

P. H. Lalik ◽

D. S. Krafte ◽

W. A. Volberg ◽

R. B. Ciccarelli

Keyword(s):

Rat Brain ◽

Chinese Hamster Ovary ◽

Chinese Hamster Ovary Cells ◽

Chinese Hamster ◽

Na Channel ◽

Ovary Cells ◽

Channel Gene ◽

Na Currents ◽

Inward Currents ◽

Dna Primers

Chinese hamster ovary (CHO-K1) cells were observed to display transient inward Na+ currents of average amplitude (-92 +/- 20 pA), which activated at voltages more than -40 mV, and peak inward currents were observed at potentials equal to or more than +10 mV. Inward Na+ currents in these cells were eliminated after treatment with 500 or 50 nM tetrodotoxin (TTX), whereas 5 nM TTX resulted in 64 +/- 10% inhibition of Na+ current. Using DNA primers designed to bind to the rat brain IIA Na+ channel subtype, we amplified specific polymerase chain reaction (PCR) fragments from CHO-K1 poly-(A)+RNA. The cloning and sequencing of two of these fragments confirmed the presence of an endogenously expressed Na+ channel gene in these cells, which we have termed cho 1. Comparison of the DNA sequence of cho 1 PCR fragments with other known Na+ channel genes indicated a high degree of homology with rat brain Na+ channel subtypes. Northern blots using riboprobes generated from the cho 1 PCR fragments revealed the presence of a specific 9-kb mRNA in these cells. The molecular and electrophysiological data suggest that the cho 1 Na+ channel gene from CHO-K1 cells is closely related to brain-type Na+ channels.

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