Biomaterial Database

Comparison of the effects of potassium and membrane potential on the calcium-dependent sodium efflux in squid axons. 1986

T J Allen, and P F Baker

Experiments are described in which the [Ca]o-dependent component of 22Na efflux is monitored under conditions of membrane potential control by voltage clamp. The apparent affinity of the efflux system for external Ca is very low in choline sea water (apparent KD approximately 50 mM); but increases dramatically when choline is replaced isosmotically by Li or K (apparent KD approximately 1-2 mM). Ca influx changes in a parallel fashion. Tris behaves much like choline and guanidinium is about two-thirds as effective as Li. Replacement of Li by K has little effect on the apparent affinity for external Ca but brings about a small (30-40%) increase in the maximal flux. The increase in maximum flux can be removed by electrical hyperpolarization to the potential before application of K and, in the absence of K, can be mimicked by electrical depolarization. These experiments suggest that the stimulatory effect of K on the Ca-dependent Na efflux into Li sea water is electrical in origin. Partial replacement of choline by K stimulates the Ca-dependent Na efflux; but only part of this stimulation can be removed by electrical hyperpolarization and, in the absence of K, electrical depolarization only brings about a relatively small stimulation. This is because only part of the stimulation that follows addition of K to choline sea waters is electrical in origin: the rest reflects an increase in the apparent affinity for external Ca that is brought about by K acting chemically. The maximum efflux into K is about 40% higher than that into choline. That this may reflect an electrical effect is supported by the observation that electrical depolarization increases the flux into choline sea water containing 110 mM-Ca where the Ca-binding site is close to saturation. The voltage clamp was used to determine the voltage dependence of the Ca-dependent Na efflux into Li sea water, choline sea water and choline sea water containing 100 mM-Na. In all three cases the flux increased with depolarization and was still rising at +70 mV. The dependence on potential was not very steep, an e-fold increase occurred over approximately 50 mV.

UI	MeSH Term	Description	Entries
D008094	Lithium	An element in the alkali metals family. It has the atomic symbol Li, atomic number 3, and atomic weight [6.938; 6.997]. Salts of lithium are used in treating BIPOLAR DISORDER.	Lithium-7,Lithium 7
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.
D002118	Calcium	A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes.	Coagulation Factor IV,Factor IV,Blood Coagulation Factor IV,Calcium-40,Calcium 40,Factor IV, Coagulation
D002794	Choline	A basic constituent of lecithin that is found in many plants and animal organs. It is important as a precursor of acetylcholine, as a methyl donor in various metabolic processes, and in lipid metabolism.	Bursine,Fagine,Vidine,2-Hydroxy-N,N,N-trimethylethanaminium,Choline Bitartrate,Choline Chloride,Choline Citrate,Choline Hydroxide,Choline O-Sulfate,Bitartrate, Choline,Chloride, Choline,Choline O Sulfate,Citrate, Choline,Hydroxide, Choline,O-Sulfate, Choline
D006146	Guanidines	A family of iminourea derivatives. The parent compound has been isolated from mushrooms, corn germ, rice hulls, mussels, earthworms, and turnip juice. Derivatives may have antiviral and antifungal properties.
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
D013997	Time Factors	Elements of limited time intervals, contributing to particular results or situations.	Time Series,Factor, Time,Time Factor