Switch to
| Predicate | Object |
|---|---|
| rdf:type | |
| lifeskim:mentions | |
| pubmed:issue |
6
|
| pubmed:dateCreated |
1992-12-23
|
| pubmed:abstractText |
The calcium (Ca2+) uptake by brush border membrane vesicles isolated from fresh human placentas has been characterized. This process was saturable and time- and concentration-dependent. It exhibited a double Michaelis-Menten kinetics, with apparent Km values of 0.17 +/- 0.03 and 2.98 +/- 0.17 mM Ca2+, and Vmax values of 0.9 +/- 0.13 and 2.51 +/- 0.45 pmol.micrograms-1.5 s-1. It was not influenced by the presence of Na+ or Mg2+ in the incubation medium. It was not increased by K+ or anion diffusion potentials, inside negative. At a steady state of 1 mM Ca2+ uptake, a large proportion (approximately 94%) of the Ca2+ was bound to the internal surface of the membranes. Preincubation of these membrane vesicles with voltage-dependent Ca2+ channel blockers (nifedipine and verapamil) had no influence on Ca2+ uptake. However, this uptake was very sensitive to pH. In the absence of a pH gradient, the Ca2+ uptake increased with alkalinity. When the intravesicular pH was kept constant while the pH of the incubation medium was increased, Ca2+ uptake was also stimulated by alkaline pH. In contrast, when the pH of the incubation medium was kept constant and the intravesicular pH was progressively increased, Ca2+ uptake was diminished with alkaline pH. Therefore, H+ gradient (H+ in trans-position greater than H+ in cis-position) favored Ca2+ transport, suggesting a H+/Ca2+ exchange mechanism. Finally, in contrast to the basal plasma membrane, the brush border membrane did not show any ATP-dependent Ca2+ transport activity.
|
| pubmed:language |
eng
|
| pubmed:journal | |
| pubmed:citationSubset |
IM
|
| pubmed:chemical |
http://linkedlifedata.com/resource/pubmed/chemical/Adenosine Triphosphate,
http://linkedlifedata.com/resource/pubmed/chemical/Calcium,
http://linkedlifedata.com/resource/pubmed/chemical/Calcium Radioisotopes,
http://linkedlifedata.com/resource/pubmed/chemical/Calcium-Binding Proteins,
http://linkedlifedata.com/resource/pubmed/chemical/Magnesium,
http://linkedlifedata.com/resource/pubmed/chemical/Nifedipine,
http://linkedlifedata.com/resource/pubmed/chemical/Sodium,
http://linkedlifedata.com/resource/pubmed/chemical/Verapamil
|
| pubmed:status |
MEDLINE
|
| pubmed:month |
Jun
|
| pubmed:issn |
0008-4212
|
| pubmed:author | |
| pubmed:issnType |
Print
|
| pubmed:volume |
70
|
| pubmed:owner |
NLM
|
| pubmed:authorsComplete |
Y
|
| pubmed:pagination |
835-42
|
| pubmed:dateRevised |
2006-11-15
|
| pubmed:meshHeading |
pubmed-meshheading:1423028-Adenosine Triphosphate,
pubmed-meshheading:1423028-Biological Transport,
pubmed-meshheading:1423028-Calcium,
pubmed-meshheading:1423028-Calcium Radioisotopes,
pubmed-meshheading:1423028-Calcium-Binding Proteins,
pubmed-meshheading:1423028-Electrophysiology,
pubmed-meshheading:1423028-Female,
pubmed-meshheading:1423028-Humans,
pubmed-meshheading:1423028-Hydrogen-Ion Concentration,
pubmed-meshheading:1423028-Magnesium,
pubmed-meshheading:1423028-Membrane Potentials,
pubmed-meshheading:1423028-Microvilli,
pubmed-meshheading:1423028-Nifedipine,
pubmed-meshheading:1423028-Placenta,
pubmed-meshheading:1423028-Pregnancy,
pubmed-meshheading:1423028-Sensitivity and Specificity,
pubmed-meshheading:1423028-Sodium,
pubmed-meshheading:1423028-Trophoblasts,
pubmed-meshheading:1423028-Verapamil
|
| pubmed:year |
1992
|
| pubmed:articleTitle |
Ca2+ transport through the brush border membrane of human placenta syncytiotrophoblasts.
|
| pubmed:affiliation |
Maisonneuve-Rosemont Hospital, Montréal (Qué.), Canada.
|
| pubmed:publicationType |
Journal Article,
In Vitro,
Research Support, Non-U.S. Gov't
|