Biomaterial Database

Slow inactivation of the sodium conductance in squid giant axons. Pronase resistance. 1978

B Rudy

1. Squid giant axons internally perfused with CsF have their Na conductance inactivated due to the low value of the resting potential. When hyperpolarized with voltage clamp to normal values of resting potential, the Na conductance recovers with an exponential time course. The time constant of recovery is of the order of 30 sec at a membrane potential of -70 mV and at 5 degrees C. The recovery from slow inactivation has a Q10 of about 3. 2. The development of inactivation during depolarization is also slow. The time constant varies between 10 and 20 sec at 5 degrees C, depending upon the value of the membrane potential. 3. Slow inactivation is also observed in NaF perfused axons and in intact axons with a low resting potential. 4. Although internal perfusion with pronase (or a purified fraction of this enzymic complex) blocks the fast (h) inactivation of the Na conductance, the slow inactivation remains. The recovery is similar before and after the proteolytic treatment. However, slow inactivation appears to develop faster after enzymic perfusion. 5. Slow inactivation develops without any apparent change in distributed or local membrane surface charge. 6. The experiments suggest that slow inactivation is a general property of the Na conductance as in many other conductance channels in excitable membranes. The experiments can be interpreted by proposing that slow inactivation is a phenomenon independent of fast inactivation, and that pronase somehow accelerates the onset of slow inactivation. 7. An alternative model, in which slow inactivation is coupled to fast inactivation, is proposed. This model is consistent with the results presented here and is very similar to one proposed to explain the frequency response of the sodium currents in Myxicola giant axons (Rudy, 1975, 1978).

UI	MeSH Term	Description	Entries
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
D011402	Pronase	A proteolytic enzyme obtained from Streptomyces griseus.	Pronase E,Pronase P,Protease XIV,XIV, Protease
D004553	Electric Conductivity	The ability of a substrate to allow the passage of ELECTRONS.	Electrical Conductivity,Conductivity, Electric,Conductivity, Electrical
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
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
D066298	In Vitro Techniques	Methods to study reactions or processes taking place in an artificial environment outside the living organism.	In Vitro Test,In Vitro Testing,In Vitro Tests,In Vitro as Topic,In Vitro,In Vitro Technique,In Vitro Testings,Technique, In Vitro,Techniques, In Vitro,Test, In Vitro,Testing, In Vitro,Testings, In Vitro,Tests, In Vitro,Vitro Testing, In