Abstract
Npt2a is responsible for 70% of phosphate (Pi) reabsorption by kidney proximal tubules. The intracellular events leading to apical membrane (AM) trafficking of Npt2a remain unknown. We hypothesized that regulation of apical membrane trafficking of Npt2a is dependent on actin cytoskeleton (AC) and SNARE protein interactions. To study AM trafficking, we first treated opossum kidney (OK) cells with parathyroid hormone to deplete Npt2a followed by treatment with low Pi medium (24 h) to stimulate AM trafficking +/− pharmacologic agents that disrupt AC. Disruption of AC by colchicine (1μM, 83.6%) and cytochalasin D (30 μM, 72.5%) significantly impaired AM trafficking of Npt2a. Surprisingly, Pi transport was not significantly impaired. To determine SNARE dependence of AM trafficking of Npt2a, we transduced SNAP23 and syntaxin, peptide inhibitors of SNARE protein interactions, prior to low Pi treatment. Npt2a AM trafficking was inhibited both by SNAP23 (51.7%) and syntaxin (25.8%). SNAP23 decreased AM trafficking of PiT2 (26.2%) but not syntaxin peptide. Our data support our hypothesis and suggest that AM trafficking of Na-Pi cotransporters is differentially regulated. Funds: VAMC and AHA.
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