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| Predicate | Object |
|---|---|
| rdf:type | |
| lifeskim:mentions | |
| pubmed:issue |
1
|
| pubmed:dateCreated |
1984-7-30
|
| pubmed:abstractText |
Basolateral plasma membranes from rat kidney cortex have been purified 40-fold by a combination of differential centrifugation, centrifugation in a discontinuous sucrose gradient followed by centrifugation in 8% percoll. The ratio of leaky membrane vesicles (L) versus right-side-out (RO) and inside-out (IO) resealed vesicles appeared to be L:RO:IO = 4:3:1. High-affinity Ca2+-ATPase, ATP-dependent Ca2+ transport and Na+/Ca2+ exchange have been studied with special emphasis on the relative transport capacities of the two Ca2+ transport systems. The kinetic parameters of Ca2+-ATPase activity in digitonin-treated membranes are: Km = 0.11 microM Ca2+ and Vmax = 81 +/- 4 nmol Pi/min X mg protein at 37 degrees C. ATP-dependent Ca2+ transport amounts to 4.3 +/- 0.2 and 7.4 +/- 0.3 nmol Ca2+/min X mg protein at 25 and 37 degrees C, respectively, with an affinity for Ca2+ of 0.13 and 0.07 microM at 25 and 37 degrees C. After correction for the percentage of IO-resealed vesicles involved in ATP-dependent Ca2+ transport, a stoichiometry of 0.7 mol Ca2+ transported per mol ATP is found for the Ca2+-ATPase. In the presence of 75 mM Na+ in the incubation medium ATP-dependent Ca2+ uptake is inhibited 22%. When Na+ is present at 5 mM an extra Ca2+ accumulation is observed which amounts to 15% of the ATP-dependent Ca2+ transport rate. This extra Ca2+ accumulation induced by low Na+ is fully inhibited by preincubation of the vesicles with 1 mM ouabain, which indicates that (Na+-K+)-ATPase generates a Na+ gradient favorable for Ca2+ accumulation via the Na+/Ca2+ exchanger. In the absence of ATP, a Na+ gradient-dependent Ca2+ uptake is measured which rate amounts to 5% of the ATP-dependent Ca2+ transport capacity. The Na+ gradient-dependent Ca2+ uptake is abolished by the ionophore monensin but not influenced by the presence of valinomycin. The affinity of the Na+/Ca2+ exchange system for Ca2+ is between 0.1 and 0.2 microM Ca2+, in the presence as well as in the absence of ATP. This affinity is surprisingly close to the affinity measured for the ATP-dependent Ca2+ pump. Based on these observations it is concluded that in isolated basolateral membranes from rat kidney cortex the Ca2+-ATPase system exceeds the capacity of the Na+/Ca2+ exchanger four- to fivefold and it is therefore unlikely that the latter system plays a primary role in the Ca2+ homeostasis of rat kidney cortex cells.
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| pubmed:language |
eng
|
| pubmed:journal | |
| pubmed:citationSubset |
IM
|
| pubmed:chemical | |
| pubmed:status |
MEDLINE
|
| pubmed:issn |
0022-2631
|
| pubmed:author | |
| pubmed:issnType |
Print
|
| pubmed:volume |
79
|
| pubmed:owner |
NLM
|
| pubmed:authorsComplete |
Y
|
| pubmed:pagination |
19-31
|
| pubmed:dateRevised |
2006-11-15
|
| pubmed:meshHeading |
pubmed-meshheading:6737462-Adenosine Triphosphate,
pubmed-meshheading:6737462-Animals,
pubmed-meshheading:6737462-Biological Transport,
pubmed-meshheading:6737462-Calcium,
pubmed-meshheading:6737462-Cell Membrane,
pubmed-meshheading:6737462-Kidney Cortex,
pubmed-meshheading:6737462-Kinetics,
pubmed-meshheading:6737462-Male,
pubmed-meshheading:6737462-Rats,
pubmed-meshheading:6737462-Rats, Inbred Strains,
pubmed-meshheading:6737462-Sodium
|
| pubmed:year |
1984
|
| pubmed:articleTitle |
Kinetic properties of the ATP-dependent Ca2+ pump and the Na+/Ca2+ exchange system in basolateral membranes from rat kidney cortex.
|
| pubmed:publicationType |
Journal Article,
In Vitro,
Research Support, Non-U.S. Gov't
|