Biomaterial Database

Induction and removal of inward-going rectification in sheep cardiac Purkinje fibres. 1982

E Carmeliet

1. In sheep cardiac Purkinje fibres superfused with K-free, Na-free medium, the membrane potential can be stable either at a low negative level (-50 mV) or at a high negative level (-100 mV). The mechanism underlying the existence of these two stable potential levels was investigated using the two-micro-electrode voltage-clamp technique.2. By applying a voltage clamp of a certain duration at an appropriate level the membrane potential could be shifted from one stable level to the other. The shift was observed in Cl-free medium, excluding a redistribution of Cl as a possible explanation.3. Currents during and following a voltage step and their change with amplitude and duration of the voltage step could not be explained on the basis of depletion or accumulation of K ions in the narrow extracellular clefts.4. Instantaneous currents determined from the high negative resting level showed a high conductance and a pronounced inward rectification, while measurements from the low negative resting level indicated a low conductance and absence of inward rectification. The steady-state current-voltage relation was dependent on the holding potential and showed memory or hysteresis.5. Estimation of the conductance by superimposed short voltage-clamp pulses showed an increase in conductance during a hyperpolarizing clamp from the low negative level and a decrease in conductance during a depolarizing clamp from the high negative level. The time-dependent current during a hyperpolarizing clamp from the low negative level reversed direction at a potential level corresponding to E(K), assuming a cleft K concentration of about 1 mM. In the presence of 0.1 mM-Ba the time-dependent current was abolished.6. The results suggest that the shift between the two stable levels is due to a time-dependent conductance change in the K inward rectifier channel, i(K1). The existence of memory excludes activation or de-activation only depending on the voltage gradient. Interaction of extracellular K ions with a site in the membrane is proposed as the activating mechanism.

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
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.
D011690	Purkinje Fibers	Modified cardiac muscle fibers composing the terminal portion of the heart conduction system.	Purkinje Fiber,Fiber, Purkinje,Fibers, Purkinje
D004553	Electric Conductivity	The ability of a substrate to allow the passage of ELECTRONS.	Electrical Conductivity,Conductivity, Electric,Conductivity, Electrical
D006329	Heart Conduction System	An impulse-conducting system composed of modified cardiac muscle, having the power of spontaneous rhythmicity and conduction more highly developed than the rest of the heart.	Conduction System, Heart,Conduction Systems, Heart,Heart Conduction Systems,System, Heart Conduction,Systems, Heart Conduction
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
D001464	Barium	An element of the alkaline earth group of metals. It has an atomic symbol Ba, atomic number 56, and atomic weight 138. All of its acid-soluble salts are poisonous.
D012756	Sheep	Any of the ruminant mammals with curved horns in the genus Ovis, family Bovidae. They possess lachrymal grooves and interdigital glands, which are absent in GOATS.	Ovis,Sheep, Dall,Dall Sheep,Ovis dalli
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