Structure-function relationships of the sodium channel expressed in Xenopus oocytes have been investigated by the combined use of site-directed mutagenesis and patch-clamp recording. This study provides evidence that the positive charges in segment S4 are involved in the voltage-sensing mechanism for activation of the channel and that the region between repeats III and IV is important for its inactivation.

/pdf/structural-parts-involved-in-activation-and-inactivation-of-353wiuvbhc.pdf

Structural parts involved in activation and inactivation of the sodium channel.

Voltage-sensitive ion channels mediate action potentials in electrically excitable cells and play important roles in signal transduction in other cell types. In the past several years, their protein components have been identified, isolated, and restored to functional form in the purified state. Na+ and Ca2+ channels consist of a principal transmembrane subunit, which forms the ion-conducting pore and is expressed with a variable number of associated subunits in different cell types. The principal subunits of voltage-sensitive Na+, Ca2+, and K+ channels are homologous members of a gene family. Models relating the primary structures of these principal subunits to their functional properties have been proposed, and experimental results have begun to define a functional map of these proteins. Coordinated application of biochemical, biophysical, and molecular genetic methods should lead to a clear understanding of the molecular basis of electrical excitability.

http://science.sciencemag.org/content/sci/242/4875/50.full.pdf

Structure and function of voltage-sensitive ion channels

The voltage-sensitive ion channels are responsible for generation of conducted action potentials in excitable cells and for a wide range of regulatory events in nonexcitable cells. On depolarization, permeability to sodium, calcium, or potassium increases dramatically over a period of 0.5 to hundreds of milliseconds and then decreases to the baseline level over a period of 2 msec to seconds. This biphasic behavior is described in terms of two experimentally separable processes that control ion channel function: activation, which controls the rate and voltage dependence of the ion permeability increase following depolarization, and inactivation, which controls the rate and voltage dependence of the subsequent return of ion permeability to the resting level during a maintained depolarization. These channels can therefore exist in three functionally distinct states or groups of states: resting, active, and inactivated. Both resting and inactivated states are nonconducting, but channels that have been inactivated by prolonged depolarization are refractory unless the cell is repolarized to allow them to return to the resting state.

/pdf/structure-and-function-of-voltage-gated-ion-channels-3orozb24cv.pdf

Structure and function of voltage-gated ion channels.

IN cardiac muscle, where Ca2+ influx across the sarcolemma is essential for contraction, the dihydropyridine (DHP)-sensitive L-type calcium channel1 represents the major entry pathway of extracellular Ca2+. We have previously elucidated the primary structure of the rabbit skeletal muscle DHP receptor by cloning and sequencing the complementary DNA2. An expression plasmid carrying this cDNA, microinjected into cultured skeletal muscle cells from mice with muscular dysgenesis, has been shown to restore both excitation-contraction coupling and slow calcium current missing from these cells, so that a dual role for the DHP receptor in skeletal muscle transverse tubules is suggested3. We report here the complete amino-acid sequence of the rabbit cardiac DHP receptor, deduced from the cDNA sequence. We also show that messenger RNA derived from the cardiac DHP receptor cDNA is sufficient to direct the formation of a functional DHP-sensitive calcium channel in Xenopus oocytes. Furthermore, higher calcium-channel activity is observed when mRNA specific for the polypeptide of relative molecular mass ∼140,000 (α2-subunit)4–6 associated with the skeletal muscle DHP receptor is co-injected.

Primary structure and functional expression of the cardiac dihydropyridine-sensitive calcium channel

Microinjection of an expression plasmid that carries complementary DNA encoding the receptor for dihydropyridine calcium channel blockers of skeletal muscle restores both excitation-contraction coupling and slow calcium current in cultured skeletal muscle cells from mice with muscular dysgenesis. This suggests that the dihydropyridine receptor in the transverse tubule membrane of skeletal muscle functions both as the voltage sensor for excitation-contraction coupling and as the slow calcium channel.

Restoration of excitation—contraction coupling and slow calcium current in dysgenic muscle by dihydropyridine receptor complementary DNA

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2888%2980615-X

Synniive Beckh

Papers

Functional expression of cloned cDNA encoding sodium channel III