Biomaterial Database

Fast and slow steps in the activation of sodium channels. 1979

C M Armstrong, and W F Gilly

Kinetic features of sodium conductance (gNa) and associated gating current (Ig) were studied in voltage-clamped, internally perfused squid axons. Following a step depolarization Ig ON has several kinetic components: (a) a rapid, early phase largely preceding gNa turn-on; (b) a delayed intermediate component developing as gNa increases; and (c) a slow component continuing after gNa is fully activated. With small depolarizations the early phase shows a quick rise (less than 40 mus) and smooth decay; the slow component is not detectable. During large pulses all three components are present, and the earliest shows a rising phase or initial plateau lasting approximately 80 mus. Steady-state and kinetic features of Ig are minimally influenced by control pulse currents, provided controls are restricted to a sufficiently negative voltage range. Ig OFF following a strong brief pulse also shows a rising phase. A depolarizing prepulse producing gNa inactivation and Ig immobilization eliminates the rising phase of Ig OFF. gNa, the immobilized portion of Ig ON, and the rising phase reappear with similar time-courses when tested with a second depolarizing pulse after varying periods of repolarization. 30 mM external ZnCl2 delays and slows gNa activation, prolongs the rising phase, and slows the subsequent decay of Ig ON. Zn does not affect the kinetics of gNa tails or Ig OFF as channels close, however. We present a sequential kinetic model of Na channel activation, which adequately describes the observations. The rapid early phase of IgON is generated by a series of several fast steps, while the intermediate component reflects a subsequent step. The slow component is too slow to be clearly associated with gNa activation.

UI	MeSH Term	Description	Entries
D007473	Ion Channels	Gated, ion-selective glycoproteins that traverse membranes. The stimulus for ION CHANNEL GATING can be due to a variety of stimuli such as LIGANDS, a TRANSMEMBRANE POTENTIAL DIFFERENCE, mechanical deformation or through INTRACELLULAR SIGNALING PEPTIDES AND PROTEINS.	Membrane Channels,Ion Channel,Ionic Channel,Ionic Channels,Membrane Channel,Channel, Ion,Channel, Ionic,Channel, Membrane,Channels, Ion,Channels, Ionic,Channels, Membrane
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008564	Membrane Potentials	The voltage differences across a membrane. For cellular membranes they are computed by subtracting the voltage measured outside the membrane from the voltage measured inside the membrane. They result from differences of inside versus outside concentration of potassium, sodium, chloride, and other ions across cells' or ORGANELLES membranes. For excitable cells, the resting membrane potentials range between -30 and -100 millivolts. Physical, chemical, or electrical stimuli can make a membrane potential more negative (hyperpolarization), or less negative (depolarization).	Resting Potentials,Transmembrane Potentials,Delta Psi,Resting Membrane Potential,Transmembrane Electrical Potential Difference,Transmembrane Potential Difference,Difference, Transmembrane Potential,Differences, Transmembrane Potential,Membrane Potential,Membrane Potential, Resting,Membrane Potentials, Resting,Potential Difference, Transmembrane,Potential Differences, Transmembrane,Potential, Membrane,Potential, Resting,Potential, Transmembrane,Potentials, Membrane,Potentials, Resting,Potentials, Transmembrane,Resting Membrane Potentials,Resting Potential,Transmembrane Potential,Transmembrane Potential Differences
D011188	Potassium	An element in the alkali group of metals with an atomic symbol K, atomic number 19, and atomic weight 39.10. It is the chief cation in the intracellular fluid of muscle and other cells. Potassium ion is a strong electrolyte that plays a significant role in the regulation of fluid volume and maintenance of the WATER-ELECTROLYTE BALANCE.
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D001369	Axons	Nerve fibers that are capable of rapidly conducting impulses away from the neuron cell body.	Axon
D012964	Sodium	A member of the alkali group of metals. It has the atomic symbol Na, atomic number 11, and atomic weight 23.	Sodium Ion Level,Sodium-23,Ion Level, Sodium,Level, Sodium Ion,Sodium 23
D015032	Zinc	A metallic element of atomic number 30 and atomic weight 65.38. It is a necessary trace element in the diet, forming an essential part of many enzymes, and playing an important role in protein synthesis and in cell division. Zinc deficiency is associated with ANEMIA, short stature, HYPOGONADISM, impaired WOUND HEALING, and geophagia. It is known by the symbol Zn.
D049832	Decapodiformes	A superorder of CEPHALOPODS comprised of squid, cuttlefish, and their relatives. Their distinguishing feature is the modification of their fourth pair of arms into tentacles, resulting in 10 limbs.	Cuttlefish,Illex,Sepiidae,Squid,Todarodes,Cuttlefishs,Decapodiforme,Illices,Squids,Todarode