K+-Ca2+ exchange

List III. Soil Properties and Experimental Conditions for Na+-Ca2+ and K+-Ca2+ Exchange Data... 

We fitted the K+-Ca2+ exchange isotherms of Bond and Phillips with a model mathematically identical to that used to fit the Na+-Ca2+ exchange data (Table II). Because the same soil was involved, we used the same value for Ks jLca but adjusted the value for /C" f) K (3.6 M ) was greater than both K s jj-Na and The K("j K value is slightly higher than the value of 2.0 M 1... 

Figure 9. Composite isotherm for K Ca2+ exchange on Brucedale clay soil for various TOTK and TOTCa concentrations. [Data (representative points shown) are from reference 17.] Curves are fits obtained with physicochemical ion-...

Figure 10. Empirical fits of K+-Ca2+ exchange data from reference 17. Curves...

KsjS k = 3.6 M-1 Adjusted to fit the K+-Ca2+ exchange data of Bond and Phillips (17), with fixed at value determined in fitting Na+-Ca2+... 

Figure 8. Predicted concentrations of major surface and solution species in monovalent-divalent exchange model fits of Figures 7 and 9. The diffuse-layer species represent the excess (K+, Na+, Ca2+) or deficit (Cl ) of ions relative to the bulk solution. Part a log C versus log TOTNa for fit of Na+-Ca2+ exchange data (Figure 7) without consideration of surface complexation. Part b log C versus log TOTNa for fit of Na+-Ca2+ exchange data (Figure 7) with surface complexation of Na+ and Ca2+. Part c log C versus log TOTKforfit of K+-Ca2+ exchange data (Figure 9) with surface complexation of K+-Ca2+. Continued on next page.

Additional cellular events linked to the activity of blood pressure regulating substances involve membrane sodium transport mechanisms Na+/K.+ ATPase Na+fLi countertransport Na+ -H exchange Na+-Ca2+ exchange Na+-K+ 2C1 transport passive Na+ transport potassium channels cell volume and intracellular pH changes and calcium channels. 

Before we impose complex barriers to reaction, we observe that more limited barriers are found even in quite soluble salt solutions. Small ions, such as Mg2+ and also Ni2+, do not exchange very easily even the water from around themselves with bulk water, in contrast with the behaviour of Na+, K+, Ca2+ and Zn2+ (Figure 2.7). 

Genetic evidence supports the importance of coordinated expression and distributions of a2 or a3 Na+/K+ pump isoforms with the Na+/Ca2+ exchanger (NCX) and Ca2+ pumps to function in excitable and contractile cells deletion of one copy of the a2 Na+/K+ pump gene in mice leads to increased contractile force in cardiac and skeletal muscle while deletion of one copy of the al gene leads to reduction of contractile force [25]. In rat optic nerve astrocytes, deletion of the a2 gene or ouabain treatment of cells expressing a2 leads to increased capacitative calcium entrance responses, which reflect a decreased ability to rapidly remove cytosolic Ca2+ [26]. 

Fink K, Meder WP, Clusmann H, Gothert M (2002) Ca2+ entry via P/Q-Type Ca2+ channels and the Na+/Ca2+ exchanger in rat and human neocortical synaptosomes. Naunyn Schmiedebergs Arch Pharmacol 366 458 163... 

Figure 1.3 Selective-binding sites in transport proteins for Na+, K+, Ca2+ and Cl. (a) Two Na+ binding sites in the LeuT Na+-dependent pump, (b) Four K+ binding sites in the KcsA K+ channel, (c) Two Ca2+ binding sites in the Ca2+ ATPase pump, (d) Two central Cl binding sites in a mutant C1C Cl /H+ exchanger. (From Gouax and MacKinnon, 2005. Copyright (2005) American Association for the Advancement of Science.)...

Finally, we should mention the K+-dependent family of Na+/Ca2+ exchangers (NCKX), the first of which was discovered in retinal photoreceptors, which cotransport Ca2+ and K+ from the cytosol into the extracellular space, in exchange for the entry of Na+, with a stoichiometry of one K+ and one Ca2+ for four Na+. 

In the case of cytochrome c, these electrostatic terms are due to changes in the redox states of the internally bound protein metal ion. In other cases where the charges on anions or cations are numerically fixed, the ions can dissociate (e.g., as the metal ion leaves the protein) or migrate (e.g., Na% K+, Ca2+, Cl-, HPO2, H+). If the exchange of these ions involves sites, especially hydrophobic sites, deep inside proteins, on the one hand, and free solution or surface sites, on the other hand, then they will be expected to have an electrostatic influence on the protein much as in a change of redox state. Thus we look next at two calcium binding proteins and later at insulin. 

Ankyrins are intracellular proteins that associate with a variety of transport proteins including Na+ channels, Na +, K+ ATPase, Na +, Ca2+ exchange, Ca2+ release channels. 

Because K+ does not recycle across the apical membrane of the DCT as it does in the TAL, there is no lumen-positive potential in this segment, and Ca2+ and Mg2+ are not driven out of the tubular lumen by electrical forces. Instead, Ca2+ is actively reabsorbed by the DCT epithelial cell via an apical Ca2+ channel and basolateral Na+/Ca2+ exchanger (Figure 15-4). This process is regulated by parathyroid hormone. 

Lithium is closely related to sodium in its properties. It can substitute for sodium in generating action potentials and in Na + -Na+ exchange across the membrane. It inhibits the latter process that is, Li+-Na+ exchange is gradually slowed after lithium is introduced into the body. At therapeutic concentrations (around 1 mmol/L), it does not significantly affect the Na + -Ca2+ exchanger or the Na +, K+ ATPase pump. 

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