Evidence against parallel operation of sodium/calcium antiport and ATP-driven calcium transport in plasma membrane vesicles from kidney tubule cells
| Autor: | Karl-Heinz Menke, Kurt R.H. Repke, Werner Schönfeld, Reinhild Schönfeld |
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| Rok vydání: | 1984 |
| Předmět: |
Antiporter
Guinea Pigs Biophysics Biochemistry Sodium-Calcium Exchanger Adenosine Triphosphate Animals Na+/K+-ATPase Transcellular Ion transporter Reabsorption Chemistry Vesicle Cell Membrane Sodium Cell Biology Basolateral plasma membrane Kinetics Kidney Tubules Plasma membrane Ca2+ ATPase Calcium Sodium-Potassium-Exchanging ATPase Carrier Proteins Mathematics |
| Zdroj: | Biochimica et Biophysica Acta (BBA) - Biomembranes. 770:183-194 |
| ISSN: | 0005-2736 |
| DOI: | 10.1016/0005-2736(84)90129-9 |
| Popis: | The present study aimed to clarify the existence of a Na+/Ca2+ antiport device in kidney tubular epithelial cells discussed in the literature to represent the predominant mechanistic device for Ca2+ reabsorption in the kidney. (1) Inside-out oriented plasma membrane vesicles from tubular epithelial cells of guinea-pig kidney showed an ATP-driven Ca2+ transport machinery similar to that known to reside in the plasma membrane of numerous cell types. It was not affected by digitalis compounds which otherwise are well-documented inhibitors of Ca2+ reabsorption. (2) The vesicle preparation contained high, digitalis-sensitive (Na++K+-ATPase activities indicating its origin from the basolateral portion of plasma membrane. (3) The operation of Na+/Ca2+ antiport device was excluded by the findings that steep Ca2+ gradients formed by ATP-dependent Ca2+ accumulation in the vesicles were not discharged by extravesicular Na+, and did not drive 45Ca2+ uptake into the vesicles via a Ca2+-45Ca2+ exchange. (4) The ATP-dependent Ca2+ uptake into the vesicles became increasingly depressed with time by extravesicular Na+. This was not due to an impairment of the Ca2+ pump itself, but caused by Na+/Ca2+ competition for binding sites on the intravesicular membrane surface shown to be important for high Ca2+ accumulation in the vesicles. (5) Earlier observations on Na+-induced release of Ca2+ from vesicles pre-equilibrated with Ca2+, seemingly favoring the existence of a Na+/Ca2+ antiporter in the basolateral plasma membrane, were likewise explained by the occurrence of Na+/Ca2+ competition for binding sites. The weight of our findings disfavors the transcellular pathway of Ca2+ reabsorption through tubule epithelium essentially depending on the operation of a Na+/Ca2+ antiport device. |
| Databáze: | OpenAIRE |
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