Potassium activators

Na+/K+-ATPase sodium pump Sodium- and potassium-activated adenosine 5 -triphosphatase EC 3.6.1.37. 

A. Chvatal, R Jendelova, N. Krizi, and E. Sykova, Stimulation-evoked changes in extracellular pH, calcium and potassium activity in the frog spinal cord. Physiologia Bohemoslovaca. 37, 203-212 (1988). 

Interaction of alkali metals with naturally-occurring compounds is of interest in connection with the active transport of these ions and of small molecules across cell walls, and with the functioning of sodium and/or potassium activated enzymes. 

Na,K-ATPase sodium and potassium activated adenosine triphosphatase (Na pump)... 

OUABAIN A chemical of botanic origin that inhibits sodium-potassium-activated ATPase in cell membranes, thereby being toxic to the cell the selection of mutants that are resistant to the toxic effects of ouabain provides the basis of a mutation-detection system in mammalian cells. 

Branston NM, Strong AJ, Symon L (1977) Extracellular potassium activity, evoked potential and tissue blood flow. Relationships during progressive ischaemia of baboon cerebral cortex. J Neurol Sci 32 305-321... 

Removal of norepinephrine Norepinephrine may (1) diffuse out of the synaptic space and enter the general circulation, (2) be metabolized to O-methylated derivatives by post-synaptic cell membrane-associated catechol O-methyltransferase (COMT) in the synaptic space, or (3) be recaptured by an uptake system that pulls the norepinephrine back into the neuron. The uptake by the neuronal membrane involves a sodium-potassium activated ATPase that can be inhibited by tricyclic antidepressants such as imipramine (see p. 119), or by cocaine (see Figure 6.3). 

Figure 2.13. Solubility diagrams showing the pH range for the most stable A1-0H-S04 minerals for a potassium activity of 10-4 M and a sulfate activity of (a) 10 4 M and (b) 10-2 M (from Nordstrom, 1982b, with permission).

The crystal stmctures of several sodium- and potassium-activated enzymes have now been determined and the position of the monovalent cation estabhshed. Structural data are listed in the Protein Data Bank (PDB). They provide a clue (but not an absolute proof) to their location within the enzyme on activation. Further biochemical studies may be necessary to verify this finding. Some examples of these structures are presented here. The first example (thrombin) is a sodium-activated enzyme, but the others are potassium-activated enzymes. 

Many crystal structures of other potassium-activated enzymes have been reported. They generally require a divalent cation and are activated by a monovalent cation that also binds. Such enzymes include amylase, which has a unique Ca Na a trinuclear center, 5 -adenosyImethionine synthetase, E. coli methionine aminopeptidase in which... 

Pharmacology. Digoxin exerts its positive inotropic effect by binding to sodium- and potassium-activated adenosine triphosphatase (Na+,K+-ATPase or sodium pump)7 Inhibition of Na+,K+-... 

W4. Walker, J. L., and Ladle, R. O., Frog heart intracellular potassium activities measured with potassium microelectrodes. Am. J. Physiol. 232,E553 (1973). 

Lai JC, Leung TK, Lim L, et al. 1991. Effects of chronic manganese treatment on rat brain regional sodium-potassium-activated and magnesium-activated adenosine triphosphatase activities during development. Metab Brain Dis 6 165-174. 

If the electrode is in a solution containing a mixture of cations (or anions, if it is an anion-responsive electrode), it may respond to the other cations. Suppose, for example, we have a mixture of sodium and potassium ions and an electrode that responds to both. The Nemst equation must include an additive term for the potassium activity ... 

In biological systems, thallium is nonessential, (i.e., not required for organisms to complete their fife cycles) and toxic at high concentrations. Thal-fium(I) mimics potassium. In humans it affects potassium-activated enzymes in the brain, muscles, and skin. Symptoms of thallium poisoning can easily be attributed to other causes, which in the past has made this element popular for homicides ... 

Ion channels triggered by voltage changes along the cell membrane are termed voltage-gated ion channels (VGICs), and include channels that conduct sodium, calcium, and potassium. Activation of... 

Primary active transport systems that have been studied include the sodium-b potassium pump [25,26] (which is the sodium + potassium-activated ATPase) and the calcium ATPase [27] and include also the ATP synthesising proton pumps of mitochondria [18,28]. 

Chapter 6. Sodium-potassium-activated adenosinetriphosphate, by F.MA.H. Schuurmans Stekhoven and S.L. Banting... 

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