Effect of hypo-osmotic incubation on membrane recycling.
Incubation of alveolar macrophages in hypo-osmotic media causes a time-and temperature-dependent increase in the number of surface receptors for three different ligands. Exposure of cells to solutions of 210 mOsM or less, at 37 degrees C but not at 0 degree C, resulted in an increase in the number of surface receptors for diferric transferrin, alpha-macroglobulin-protease complexes, and mannose-terminated glycoproteins. Upon media dilution at 37 degrees C, surface receptor number reached a maximum within 5 min and returned to near-normal values by 30 min. The increase in surface receptor number was the result of a decrease in the rate of internalization of receptors, either occupied or unoccupied. The rate of receptor exteriorization was unaltered by hypo-osmotic incubation of cells. The rate of fluid-phase pinocytosis was also inhibited upon incubation in hypo-osmotic solution. In experiments in which both receptor-mediated endocytosis and fluid phase pinocytosis were measured on the same samples, inhibition of both processes occurred with the same kinetics and to a similar extent. The rate of receptor-mediated endocytosis recovered to normal rates after 60 min in hypo-osmotic solutions, whereas the rate of fluid phase pinocytosis did not recover to the same extent.
Novak
J M
JM
Department of Pathology, University of Utah College of Medicine, Salt Lake City 84132.
Ward
D M
DM
Buys
S S
SS
Kaplan
J
J
D000818:Animals; D002462:Cell Membrane / Q000502:physiology*; D004705:Endocytosis; D008264:Macrophages / Q000166:cytology; D009995:Osmosis; D010873:Pinocytosis; D011650:Pulmonary Alveoli / Q000166:cytology; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000502:physiology*; D012996:Solutions
D011956:Receptors, Cell Surface; D012996:Solutions