%0 Journal Article %1 Urba_2006_693 %A Urbanczyk, Jason %A Chernysh, Olga %A Condrescu, Madalina %A Reeves, John P %D 2006 %J J. Physiol. %K 4,5-Diphosphate, Allosteric Animals; CHO Calcium, Cells; Channel Cricetinae; Cricetulus; Cytosol, Exchanger, Factors; Gating; Ion Mutation; Phosphatidylinositol Regulation; Sodium, Sodium-Calcium Time Transfection genetics/metabolism; metabolism; %N Pt 3 %P 693--705 %R 10.1113/jphysiol.2006.113910 %T Sodium-calcium exchange does not require allosteric calcium activation at high cytosolic sodium concentrations. %U http://dx.doi.org/10.1113/jphysiol.2006.113910 %V 575 %X The activity of the cardiac Na$^+$-Ca$^2+$ exchanger (NCX1.1) is allosterically regulated by Ca$^2+$, which binds to two acidic regions in the cytosolically disposed central hydrophilic domain of the NCX protein. A mutation in one of the regulatory Ca$^2+$ binding regions (D447V) increases the half-activation constant (K(h)) for allosteric Ca$^2+$ activation from approximately 0.3 to > 1.8 microm. Chinese hamster ovary cells expressing the D447V exchanger showed little or no activity under physiological ionic conditions unless cytosolic Ca$^2+$ was elevated to > 1 microm. However, when cytosolic Na$^+$ was increased to 20 mm or more (using ouabain-induced inhibition of the Na$^+$,K$^+$-ATPase or the ionophore gramicidin), cells expressing the D447V mutant rapidly accumulated Ca$^2+$ or Ba$^2+$ when the reverse (Ca$^2+$ influx) mode of NCX activity was initiated, although initial cytosolic Ca$^2+$ was < 100 nm. Importantly, the time course of Ca$^2+$ uptake did not display the lag phase that reflects allosteric Ca$^2+$ activation of NCX activity in the wild-type NCX1.1; indeed, at elevated Na$^+$, the D447V mutant behaved similarly to the constitutively active deletion mutant Delta(241-680), which lacks the regulatory Ca$^2+$ binding sites. In cells expressing wild-type NCX1.1, increasing concentrations of cytosolic Na$^+$ led to a progressive shortening of the lag phase for Ca$^2+$ uptake. The effects of elevated Na$^+$ developed rapidly and were fully reversible. The activity of the D447V mutant was markedly inhibited when phosphatidylinositol 4,5-bisphosphate (PIP2) levels were reduced. We conclude that when PIP2 levels are high, elevated cytosolic Na$^+$ induces a mode of exchange activity that does not require allosteric Ca$^2+$ activation.

@article{Urba_2006_693, abstract = {The activity of the cardiac {N}a$^{+}$-{C}a$^{2+}$ exchanger (NCX1.1) is allosterically regulated by {C}a$^{2+}$, which binds to two acidic regions in the cytosolically disposed central hydrophilic domain of the NCX protein. A mutation in one of the regulatory {C}a$^{2+}$ binding regions (D447V) increases the half-activation constant (K(h)) for allosteric {C}a$^{2+}$ activation from approximately 0.3 to > 1.8 microm. Chinese hamster ovary cells expressing the D447V exchanger showed little or no activity under physiological ionic conditions unless cytosolic [{C}a$^{2+}$] was elevated to > 1 microm. However, when cytosolic [{N}a$^{+}$] was increased to 20 mm or more (using ouabain-induced inhibition of the {N}a$^{+}$,{K}$^{+}$-ATPase or the ionophore gramicidin), cells expressing the D447V mutant rapidly accumulated {C}a$^{2+}$ or {B}a$^{2+}$ when the reverse ({C}a$^{2+}$ influx) mode of NCX activity was initiated, although initial cytosolic [{C}a$^{2+}$] was < 100 nm. Importantly, the time course of {C}a$^{2+}$ uptake did not display the lag phase that reflects allosteric {C}a$^{2+}$ activation of NCX activity in the wild-type NCX1.1; indeed, at elevated [{N}a$^{+}$], the D447V mutant behaved similarly to the constitutively active deletion mutant Delta(241-680), which lacks the regulatory {C}a$^{2+}$ binding sites. In cells expressing wild-type NCX1.1, increasing concentrations of cytosolic {N}a$^{+}$ led to a progressive shortening of the lag phase for {C}a$^{2+}$ uptake. The effects of elevated [{N}a$^{+}$] developed rapidly and were fully reversible. The activity of the D447V mutant was markedly inhibited when phosphatidylinositol 4,5-bisphosphate (PIP2) levels were reduced. We conclude that when PIP2 levels are high, elevated cytosolic [{N}a$^{+}$] induces a mode of exchange activity that does not require allosteric {C}a$^{2+}$ activation.}, added-at = {2009-06-03T11:20:58.000+0200}, author = {Urbanczyk, Jason and Chernysh, Olga and Condrescu, Madalina and Reeves, John P}, biburl = {https://www.bibsonomy.org/bibtex/25388e89807d6899e036813e2f442ac4a/hake}, description = {The whole bibliography file I use.}, doi = {10.1113/jphysiol.2006.113910}, file = {Urba_2006_693.pdf:Urba_2006_693.pdf:PDF}, institution = { Physiology, UMDNJ - NJ Medical School, 185 South Orange Avenue, PO Box 1709, Newark, NJ 07101-1709, USA.}, interhash = {5ee1d10dd1f4fcec8398e2bac42fa3b7}, intrahash = {5388e89807d6899e036813e2f442ac4a}, journal = {J. Physiol.}, keywords = {4,5-Diphosphate, Allosteric Animals; CHO Calcium, Cells; Channel Cricetinae; Cricetulus; Cytosol, Exchanger, Factors; Gating; Ion Mutation; Phosphatidylinositol Regulation; Sodium, Sodium-Calcium Time Transfection genetics/metabolism; metabolism;}, month = Sep, number = {Pt 3}, pages = {693--705}, pdf = {Urba_2006_693.pdf}, pii = {jphysiol.2006.113910}, pmid = {16809364}, timestamp = {2009-06-03T11:21:35.000+0200}, title = {Sodium-calcium exchange does not require allosteric calcium activation at high cytosolic sodium concentrations.}, url = {http://dx.doi.org/10.1113/jphysiol.2006.113910}, volume = 575, year = 2006 }