EXPRESSION OF PARATHYROID-HORMONE RECEPTORS IN MDCK AND LLC-PK1 CELLS

Parathyroid hormone (PTH) inhibits renal proximal tubular phosphate (P-i) and bicarbonate reabsorption by regulating the activity of apical Na/P-i cotransport and Na/H exchange. Two renal epithelial cell lines [''proximal tubular'', LLC-PKi; ''distal tubular'', Madin-Darby canine kidney, (MDCK) cells] were stably transfected with complementary deoxyribonucleic acids (cDNAs) encoding a cloned PTH receptor in order to examine the polarity of transfected receptor function and whether or not intrinsic P-i transport is regulated by the transfected PTH receptor. The receptors are functionally coupled to the stimulation of adenosine 3':5' cyclic monophosphate (cAMP) production at both cell surfaces in LLC-PK1 cells, whereas this response is primarily limited to the basolateral surface in MDCK cells. Immunocytochemistry suggests an apical and basolateral localization of the transfected PTH receptor in LLC-PK, cells and only a basolateral localization in MDCK cells. PTH activation of the transfected receptors is not coupled to the regulation of intrinsic P-i transport in either LLC-PK1 or MDCK cells.