Acute regulation of Na+/H+ exchanger NHE3 by parathyroid hormone via NHE3 phosphorylation and dynamin-dependent endocytosis

Parathyroid hormone (PTH) is a potent inhibitor of mammalian renal proximal tubule Na+ transport via its action on the apical membrane Na+/H+ exchange r NHE3. In the opossum kidney cell line, inhibition of NHE3 activity was de tected from 5 to 45 min after PTH addition. Increase in NHE3 phosphorylatio n on multiple serines was evident after 5 min of PTH, but decrease in surfa ce NHE3 antigen was not detectable until after 30 min of PTH. The decrease in surface NHE3 antigen was due to increased NHE3 endocytosis. When endocyt ic trafficking was arrested with a dominant negative dynamin mutant (K44A), the early inhibition (5 min) of NHE3 activity by PTH was not affected, whe reas the late inhibition (30 min) and decreased surface NHE3 antigen induce d by PTH were abrogated. We conclude that PTH acutely inhibits NHE3 activit y in a biphasic fashion by NHE3 phosphorylation followed by dynamin-depende nt endocytosis.