A Comparison Between Calcium and Strontium Transport by the (Ca<sup>2+</sup> + Mg<sup>2+</sup>)ATPase of the Basolateral Plasma Membrane of Renal Proximal Convoluted Tubules
In this work, the utilization of calcium and strontium by the (Ca<sup>2+</sup> + Mg<sup>2+</sup>)ATPase of the basolateral plasma membrane of renal proximal convoluted tubules were compared. [<sup>90</sup>Sr]Sr<sup>2+</sup> and [<sup>45</sup&g...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2025-04-01
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| Series: | Membranes |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2077-0375/15/4/122 |
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| Summary: | In this work, the utilization of calcium and strontium by the (Ca<sup>2+</sup> + Mg<sup>2+</sup>)ATPase of the basolateral plasma membrane of renal proximal convoluted tubules were compared. [<sup>90</sup>Sr]Sr<sup>2+</sup> and [<sup>45</sup>Ca]Ca<sup>2+</sup> uptake by vesicles derived from this membrane were strictly dependent on ATP and Mg<sup>2+</sup>, and no other nucleotide was able to support the transport. Each cation inhibited the uptake of the other one in a purely competitive fashion (the same Vmax; increased K<sub>0.5</sub>), without causing a significant change in the influx rate. These results indicate that both cations bind at the same transport site on the enzyme, facing the cytosolic surface of the cell. The K<sub>0.5</sub> for Sr<sup>2+</sup> obtained for (Sr<sup>2+</sup> + Mg<sup>2+</sup>)ATPase activity was 13.1 ± 0.2 µM and for Sr<sup>2+</sup> uptake was 13.4 ± 0.1 µM. They were higher than K<sub>0.5</sub> for Ca<sup>2+</sup> obtained for (Ca<sup>2+</sup> + Mg<sup>2+</sup>)ATPase activity (0.42 ± 0.03 µM) and for Ca<sup>2+</sup> uptake (0.28 ± 0.02 µM). It is postulated that the lower ATPase affinity for Sr<sup>2+</sup> is associated with greater steric difficulties for the occupation by this cation of the binding and transport sites, as a consequence of its greater crystal ionic radius (1.13 Å for Sr<sup>2+</sup> against 0.99 Å for Ca<sup>2+</sup>). |
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| ISSN: | 2077-0375 |