Topic
Potassium
About: Potassium is a(n) research topic. Over the lifetime, 43985 publication(s) have been published within this topic receiving 654980 citation(s). The topic is also known as: K & kalium.
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TL;DR: Leg nerves from the shore crab contain an adenosine triphosphatase which is located in the submicroscopic particles, and the influence of sodium, potassium, magnesium and calcium ions on this enzyme has been investigated.
Abstract: Leg nerves from the shore crab (Carcinus maenas) contain an adenosine triphosphatase which is located in the submicroscopic particles. The influence of sodium, potassium, magnesium and calcium ions on this enzyme has been investigated.
The presence of magnesium ions is an obligatory requirement for the activity of the enzyme. Sodium ions increase the activity when magnesium ions are present. Potassium ions increase the activity when the system contains both magnesium and sodium ions. Potassium ions in high concentration inhibit that part of the activity which is due to Na+, while the activity due to Mg++ is not affected. Calcium ions inhibit the enzyme under all conditions.
When Mg++ or Mg++ + Na+ are present in the system, the optimum magnesium concentration is equal to the concentration of ATP. If potassium ions are added, the optimum magnesium concentration is doubled. If calcium ions are also added, the optimum magnesium concentration becomes still higher, and it increases with the calcium concentration.
A majority of these observations may be explained by assuming (a) that the substrate most readily attacked by the enzyme is sodium-magnesium-ATP, (b) that potassium ions stimulate the enzyme directly, and (c) that an increase in the concentration of potassium ions leads to a displacement of sodium ions from the substrate and accordingly to an inhibition of the reaction.
If the system contains the four cations in concentrations roughly equal to those in the crab-nerve axoplasm, an increase in the sodium concentration as well as a decrease in the potassium concentration will lead to an intensification of the enzyme activity. This observation, as well as some other characteristics of the system, suggest that the adenosine triphosphatase studied here may be involved in the active extrusion of sodium from the nerve fibre.
1,761 citations
TL;DR: In this article, the authors investigated the influence of different cations on the activity of an adenosine triphosphatase (ATP) enzyme in the leg nerves of crabs.
Abstract: Leg nerves from the shore crab (Carcinus maenas) contain an adenosine triphosphatase which is located in the submicroscopic particles. The influence of sodium, potassium, magnesium and calcium ions on this enzyme has been investigated.
The presence of magnesium ions is an obligatory requirement for the activity of the enzyme. Sodium ions increase the activity when magnesium ions are present. Potassium ions increase the activity when the system contains both magnesium and sodium ions. Potassium ions in high concentration inhibit that part of the activity which is due to Na+, while the activity due to Mg++ is not affected. Calcium ions inhibit the enzyme under all conditions.
When Mg++ or Mg++ + Na+ are present in the system, the optimum magnesium concentration is equal to the concentration of ATP. If potassium ions are added, the optimum magnesium concentration is doubled. If calcium ions are also added, the optimum magnesium concentration becomes still higher, and it increases with the calcium concentration.
A majority of these observations may be explained by assuming (a) that the substrate most readily attacked by the enzyme is sodium-magnesium-ATP, (b) that potassium ions stimulate the enzyme directly, and (c) that an increase in the concentration of potassium ions leads to a displacement of sodium ions from the substrate and accordingly to an inhibition of the reaction.
If the system contains the four cations in concentrations roughly equal to those in the crab-nerve axoplasm, an increase in the sodium concentration as well as a decrease in the potassium concentration will lead to an intensification of the enzyme activity. This observation, as well as some other characteristics of the system, suggest that the adenosine triphosphatase studied here may be involved in the active extrusion of sodium from the nerve fibre.
1,697 citations
TL;DR: The most widely accepted theory of the restirng potential of muscle is that the electrical potential difference between the inside and outside of a muscle fibre arises from the concentration gradients of the potassium and chloride ions.
Abstract: The most widely accepted theory of the restirng potential of muscle is that the electrical potential difference between the inside and outside of a muscle fibre arises from the concentration gradients of the potassium and chloride ions. If we follow Boyle & Conway (1941), the membrane is assumed to be permeable to K and Cl but to be impermeable or sparingly permeable to other ions. Since K is more concentrated inside and Cl is more concentrated outside, the interior of the fibre should be electrically negative to the external solution. If K and Cl are distributed passively, the concentration ratios and the membrane potential under equilibrium conditions ought to conform to the relation
1,378 citations
Book•
01 Jan 2003
TL;DR: Shirley et al. as discussed by the authors presented a list of newly discovered and other trace elements, including aluminum, Arsenic, Cadmium, Lead, and Mercury, which they termed as "natural sources of Minerals".
Abstract: Introduction. Calcium and Phosphorus. Sodium and Chlorine (Common Salt). Potassium. Magnesium. R.L. Shirley, Sulfur. Iron. Copper and Molybdenum. Cobalt. Iodine. Manganese. Zinc. Selenium. Fluorine. Aluminum, Arsenic, Cadmium, Lead, and Mercury. Newly Discovered and Other Trace Elements. Natural Sources of Minerals. Maximum Tolerance Levels. Mineral Supplementation. Bibliography. Appendixes. Index.
1,131 citations
TL;DR: It is proposed that a cyclic, energy-dissipating flux of mitochondrial calcium accounts for uncoupling by A23187, whereas inhibition of ATPase and glutamate oxidation and increased potassium permeability of mitochondria result from antibiotic-mediated magnesium efflux.
Abstract: A23187 is a carboxylic acid antibiotic which simultaneously uncouples oxidative phosphorylation and inhibits ATPase of rat liver mitochondria incubated in a magnesium-free medium. The antibiotic acts as a freely mobile carrier to transport calcium and magnesium, but not potassium, from an aqueous medium buffered at pH 7.4 into a bulk organic phase. A23187 causes a progressive release of endogenous magnesium and inorganic phosphate from mitochondria incubated with substrate, but little change in calcium or potassium content. If EDTA is added, A23187 severely depletes intramitochondrial calcium and magnesium in Release of State 4 succinate oxidation by A23187 is inhibited by lanthanum chloride, ruthenium red, ((ethylene bis)oxyethylene nitrilo)tetraacetic acid (EGTA), EDTA, MgCl2, and ATP. Inhibition by EGTA (or EDTA) of A23187′s uncoupling is reversed readily by calcium but not magnesium. In the presence of A23187 plus EGTA, mitochondria retain only 2 to 3 nmoles of Mg2+ per mg of protein but remain coupled and phosphorylate ADP at 80 to 85% of control rates with β-hydroxybutyrate or succinate as substrate. Under these conditions, coupled phosphorylation supported by glutamate, and ATP hydrolysis are severely depressed, but increasing concentrations of magnesium in the incubating medium prevent these inhibitions. It is proposed that a cyclic, energy-dissipating flux of mitochondrial calcium accounts for uncoupling by A23187, whereas inhibition of ATPase and glutamate oxidation and increased potassium permeability of mitochondria result from antibiotic-mediated magnesium efflux.
1,096 citations