THE 2 MANNOSE 6-PHOSPHATE RECEPTORS HAVE ALMOST IDENTICAL SUBCELLULAR DISTRIBUTIONS IN U937 MONOCYTES

  • 1 December 1988
    • journal article
    • research article
    • Vol. 47  (2) , 366-372
Abstract
Using a semiquantitative immunogold technique on ultrathin cryosections, the in situ subcellular distributions of the cation-dependent, 46-kDa mannose 6-phosphate receptor (small MPR) and of the cation-independent, 270-kDa mannose 6-phosphate receptor (large MPR) were for the first time compared. U937 cells were chosen because of their relatively high content of both receptor species. Of each receptor, about 12% occurred at the cell surface, 2% in the Golgi stack, and about 25% in vacuoles resembling endosomal vacuoles. About half of both receptors was found in tubules, presumably belonging to endosomes and trans-Golgi reticulum. It was concluded that the distribution of the small and large MPR were roughly similar. The only exception was formed by electron-dense vesicles occurring in the trans-Golgi region and surrounding endosomes. Dense vesicles contained significantly less small MPR (7%) than large MPR (12%).