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rdf:type | |
lifeskim:mentions |
umls-concept:C0007452,
umls-concept:C0035331,
umls-concept:C0039808,
umls-concept:C0060505,
umls-concept:C0086035,
umls-concept:C0086045,
umls-concept:C0178719,
umls-concept:C0205101,
umls-concept:C0206427,
umls-concept:C0441635,
umls-concept:C0443213,
umls-concept:C0444706,
umls-concept:C0596235,
umls-concept:C0597484,
umls-concept:C0678640,
umls-concept:C0812409,
umls-concept:C0851285,
umls-concept:C0851827,
umls-concept:C1167322,
umls-concept:C1701901,
umls-concept:C1880497,
umls-concept:C1996904,
umls-concept:C2752508
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pubmed:issue |
34
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pubmed:dateCreated |
1992-1-13
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pubmed:abstractText |
Regulation of cytosolic free Ca2+ in the physiologically relevant submicromolar range was measured in isolated intact bovine rod outer segments (ROS) with the intracellular Ca(2+)-indicating dye fluo-3. Changes in free Ca2+ were compared with changes in total Ca2+ measured with 45Ca fluxes and a good qualitative correlation was observed. Ca2+ homeostasis in isolated bovine ROS was exclusively mediated via the Na-Ca-K exchanger. Free cytosolic Ca2+ concentration was lowered by an increase in the inward Na+ gradient, was raised by an increase in external K+, and was raised by depolarization of the plasma membrane. The simplest stoichiometry consistent with these qualitative observations is 4Na:(1Ca + 1K). The individual K:Ca, Na:Ca, and K:Na coupling ratios were deduced from quantitative changes in cytosolic free Ca2+ upon changes in the transmembrane Na+ and K+ gradients. The observed changes in free Ca2+ did not agree with changes in free Ca2+ calculated on the basis of the above fixed stoichiometry which may reflect the flexibility in the Ca:K coupling ratio observed before in flux experiments (Schnetkamp, P. P. M., Szerencsei, R. T., and Basu, D. K. (1991) J. Biol. Chem. 266, 198-206). The most dramatic discrepancy was observed for the Na:Ca coupling ratio: the expected very large changes in cytosolic free Ca2+ upon changes in the transmembrane Na+ gradient were not observed. Rapid Na(+)-induced Ca2+ extrusion was unable to lower cytosolic free Ca2+ below 100 nM, even under nonequilibrium conditions and despite the observation that Ca2+ influx via reverse Na-Ca-K exchange readily occurred at a free external Ca2+ concentration of 20 nM. We conclude that the Na(+)-dependent extrusion mode of the Na-Ca-K exchanger occurs in a brief (20-s) burst of high maximal velocity transport followed by a nearly complete inactivation of transport. The importance of our findings for Ca2+ homeostasis in functioning rod photoreceptors is discussed.
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pubmed:language |
eng
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pubmed:journal | |
pubmed:citationSubset |
IM
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pubmed:chemical |
http://linkedlifedata.com/resource/pubmed/chemical/Aniline Compounds,
http://linkedlifedata.com/resource/pubmed/chemical/Calcium,
http://linkedlifedata.com/resource/pubmed/chemical/Fluo-3,
http://linkedlifedata.com/resource/pubmed/chemical/Fluorescent Dyes,
http://linkedlifedata.com/resource/pubmed/chemical/Potassium,
http://linkedlifedata.com/resource/pubmed/chemical/Sodium,
http://linkedlifedata.com/resource/pubmed/chemical/Xanthenes
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pubmed:status |
MEDLINE
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pubmed:month |
Dec
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pubmed:issn |
0021-9258
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pubmed:author | |
pubmed:issnType |
Print
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pubmed:day |
5
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pubmed:volume |
266
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pubmed:owner |
NLM
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pubmed:authorsComplete |
Y
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pubmed:pagination |
22983-90
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pubmed:dateRevised |
2008-11-21
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pubmed:meshHeading |
pubmed-meshheading:1744093-Aniline Compounds,
pubmed-meshheading:1744093-Animals,
pubmed-meshheading:1744093-Biological Transport,
pubmed-meshheading:1744093-Calcium,
pubmed-meshheading:1744093-Cattle,
pubmed-meshheading:1744093-Cytosol,
pubmed-meshheading:1744093-Fluorescent Dyes,
pubmed-meshheading:1744093-Ion Exchange,
pubmed-meshheading:1744093-Membrane Potentials,
pubmed-meshheading:1744093-Potassium,
pubmed-meshheading:1744093-Rod Cell Outer Segment,
pubmed-meshheading:1744093-Sodium,
pubmed-meshheading:1744093-Thermodynamics,
pubmed-meshheading:1744093-Xanthenes
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pubmed:year |
1991
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pubmed:articleTitle |
Regulation of intracellular free Ca2+ concentration in the outer segments of bovine retinal rods by Na-Ca-K exchange measured with fluo-3. II. Thermodynamic competence of transmembrane Na+ and K+ gradients and inactivation of Na(+)-dependent Ca2+ extrusion.
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pubmed:affiliation |
Department of Medical Biochemistry, University of Calgary, Alberta, Canada.
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pubmed:publicationType |
Journal Article,
Research Support, Non-U.S. Gov't
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