Biomaterial Database

Apparent affinity of the Na/K pump for ouabain in cultured chick cardiac myocytes. Effects of Nai and Ko. 1991

J R Stimers, and S Liu, and M Lieberman

Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710.

The measured apparent affinity (K0.5) of the Na/K pump for ouabain has been reported to vary over a wide range. In a previous report we found that changing Nai could alter apparent affinity by at least an order of magnitude and that the model presented predicted this variability. To increase our understanding of this variability, isolated cells or two- to three-cell clusters of cardiac myocytes from 11-d embryonic chick were used to measure the effects of Nai and Ko on the K0.5 of the Na/K pump for ouabain. Myocytes were whole-cell patch clamped and Na/K pump current (Ip) was measured in preparations exposed to a Ca-free modified Hank's solution (HBSS) that contained 1 mM Ba, 10 mM Cs, and 0.1 mM Cd. Under these conditions there are no Ko-sensitive currents other than Ip because removal of Ko in the presence of ouabain had no effect on the current-voltage (I-V) relation. The I-V relation for Ip showed that in the presence of 5.4 mM Ko and 51 mM Nai, Ip has a slight voltage dependence, decreasing approximately 30% from 0 to -130 mV. Increasing Nai in the patch pipette from 6 to 51 mM (Ko = 5.4 mM) caused Ip to increase from 0.46 +/- 0.07 (n = 5) to 1.34 +/- 0.08 microA/cm2 (n = 13) with a K0.5 for Nai of 17.4 mM and decreased the K0.5 for ouabain from 18.5 +/- 1.8 (n = 4) to 3.1 +/- 0.4 microM (n = 3). Similarly, varying Ko between 0.3 and 10.8 mM (Nai = 24 mM) increased Ip from 0.13 +/- 0.01 (n = 5) to 0.90 +/- 0.05 microA/cm2 (n = 5) with a K0.5 for Ko of 1.94 mM and increased K0.5 for ouabain from 0.56 +/- 0.14 (n = 3-6) to 10.0 +/- 1.1 microM (n = 6). All of these changes are predicted by the model presented. A qualitative explanation of these results is that Nai and Ko interact with the Na/K pump to shift the steady-state distribution of the Na/K pump molecules among the kinetic states. This shift in state distribution alters the probability that the Na/K pump will be in the conformation that binds ouabain with high affinity, thus altering the apparent affinity. In intact cells, the measured apparent affinity represents a combination of all the rate constants in the model and does not equate to simple first-order binding kinetics.(ABSTRACT TRUNCATED AT 400 WORDS)

UI	MeSH Term	Description	Entries
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
D008839	Microelectrodes	Electrodes with an extremely small tip, used in a voltage clamp or other apparatus to stimulate or record bioelectric potentials of single cells intracellularly or extracellularly. (Dorland, 28th ed)	Electrodes, Miniaturized,Electrode, Miniaturized,Microelectrode,Miniaturized Electrode,Miniaturized Electrodes
D008954	Models, Biological	Theoretical representations that simulate the behavior or activity of biological processes or diseases. For disease models in living animals, DISEASE MODELS, ANIMAL is available. Biological models include the use of mathematical equations, computers, and other electronic equipment.	Biological Model,Biological Models,Model, Biological,Models, Biologic,Biologic Model,Biologic Models,Model, Biologic
D008985	Monensin	An antiprotozoal agent produced by Streptomyces cinnamonensis. It exerts its effect during the development of first-generation trophozoites into first-generation schizonts within the intestinal epithelial cells. It does not interfere with hosts' development of acquired immunity to the majority of coccidial species. Monensin is a sodium and proton selective ionophore and is widely used as such in biochemical studies.	Coban,Monensin Monosodium Salt,Monensin Sodium,Monensin-A-Sodium Complex,Rumensin,Monensin A Sodium Complex
D009206	Myocardium	The muscle tissue of the HEART. It is composed of striated, involuntary muscle cells (MYOCYTES, CARDIAC) connected to form the contractile pump to generate blood flow.	Muscle, Cardiac,Muscle, Heart,Cardiac Muscle,Myocardia,Cardiac Muscles,Heart Muscle,Heart Muscles,Muscles, Cardiac,Muscles, Heart
D010042	Ouabain	A cardioactive glycoside consisting of rhamnose and ouabagenin, obtained from the seeds of Strophanthus gratus and other plants of the Apocynaceae; used like DIGITALIS. It is commonly used in cell biological studies as an inhibitor of the NA(+)-K(+)-EXCHANGING ATPASE.	Acocantherin,G-Strophanthin,Acolongifloroside K,G Strophanthin
D011487	Protein Conformation	The characteristic 3-dimensional shape of a protein, including the secondary, supersecondary (motifs), tertiary (domains) and quaternary structure of the peptide chain. PROTEIN STRUCTURE, QUATERNARY describes the conformation assumed by multimeric proteins (aggregates of more than one polypeptide chain).	Conformation, Protein,Conformations, Protein,Protein Conformations
D002478	Cells, Cultured	Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others.	Cultured Cells,Cell, Cultured,Cultured Cell
D002642	Chick Embryo	The developmental entity of a fertilized chicken egg (ZYGOTE). The developmental process begins about 24 h before the egg is laid at the BLASTODISC, a small whitish spot on the surface of the EGG YOLK. After 21 days of incubation, the embryo is fully developed before hatching.	Embryo, Chick,Chick Embryos,Embryos, Chick
D004553	Electric Conductivity	The ability of a substrate to allow the passage of ELECTRONS.	Electrical Conductivity,Conductivity, Electric,Conductivity, Electrical