Open AccessDistinct functional properties of two electrogenic isoforms of the SLC 34 Na‐Pi cotransporter
Author(s) -
Mizutani Natsuki,
Okochi Yoshifumi,
Okamura Yasushi
Publication year - 2019
Publication title -
physiological reports
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.918
H-Index - 39
ISSN - 2051-817X
DOI - 10.14814/phy2.14156
Subject(s) - pi , cotransporter , phosphatase , xenopus , phosphatidylinositol , homeostasis , biology , microbiology and biotechnology , biochemistry , chemistry , signal transduction , phosphorylation , gene , organic chemistry , sodium
Inorganic phosphate (P i ) is crucial for proper cellular function in all organisms. In mammals, type II Na‐Pi cotransporters encoded by members of the Slc34 gene family play major roles in the maintenance of P i homeostasis. However, the molecular mechanisms regulating Na‐Pi cotransporter activity within the plasma membrane are largely unknown. In the present study, we used two approaches to examine the effect of changing plasma membrane phosphatidylinositol 4,5‐bisphosphate ( PI (4,5)P 2 ) levels on the activities of two electrogenic Na‐Pi cotransporters, NaPi‐ II a and NaPi‐ II b. To deplete plasma membrane PI (4,5)P 2 in Xenopus oocytes, we utilized Ciona intestinalis voltage‐sensing phosphatase (Ci‐ VSP ), which dephosphorylates PI (4,5)P 2 to phosphatidylinositol 4‐phosphate ( PI (4)P). Upon activation of Ci‐ VSP , NaPi‐ II b currents were significantly decreased, whereas NaPi‐ II a currents were unaffected. We also used the rapamycin‐inducible Pseudojanin ( PJ ) system to deplete both PI (4,5)P 2 and PI (4)P from the plasma membrane of cultured Neuro 2a cells. Depletion of PI (4,5)P 2 and PI (4)P using PJ significantly reduced NaPi‐ II b activity, but NaPi‐ II a activity was unaffected, which excluded the possibility that NaPi‐ II a is equally sensitive to PI (4,5)P 2 and PI (4)P. These results indicate that NaPi‐ II b activity is regulated by PI (4,5)P 2 , whereas NaPi‐ II a is not sensitive to either PI (4,5)P 2 or PI (4)P. In addition, patch clamp recording of NaPi‐ II a and NaPi‐ II b currents in cultured mammalian cells enabled kinetic analysis with higher temporal resolution, revealing their distinct kinetic properties.