Parathyroid Hormone Effects on Surface Proteins of Opossum Kidney Cells

Abstract

Parathyroid hormone (PTH)-mediated effects on surface expressed proteins of opossum kidney (OK) cells grown on permeant filter supports were studied using the impermeant biotin analogue sulfo-NHS-biotin. With respect to the polarized expression in control cells, it was found that the biotinoylated (Triton X-114 extractable) protein patterns of the apical and basolateral cell surface are very similar. On top of this similarity certain labeled proteins were found to be typical for the apical (95 and 60 kD) and the basolateral membrane (80, 72, 50 and 33 kD). PTH (10–8M, 10 min) led to a 50% decrease of the staining intensity of proteins with molecular weights of 80, 72, 50 and 33 kD expressed at the basolateral membrane. No PTH-mediated effects were observed on apically expressed proteins. It is suggested that the observed decrease of staining intensities of basolateral surface proteins is due to an increased rate of internalization due to PTH. Furthermore, since the apical biotinoylated protein pattern did not change after PTH exposure, it is concluded that the general endocytotic rate at the apical cell surface is not much influenced by a short exposure to PTH.