In a cultured, renal epithelial cell line, OK, parathyroid hormone (PTH) reduces Na/phosphate cotransport and upon removal of the hormone the activity is regained. Cycloheximide, an inhibitor of protein synthesis, did not interfere with the PTH action, but prevented the reduced phosphate transport from regaining its original activity. Drugs, such as colchicine, that disrupt the microtubular network, lessened both the action of PTH and prevented the recovery of activity. The results are consistent with the irreversible inactivation of a plasma membrane protein necessary for full activity of the Na/phosphate cotransport.
