| Abstract: | We have investigated the effect of temperature on the content of surface asialoglycoprotein receptors on isolated rat hepatocytes. Receptor was determined by measuring the specific binding of 125I- or 3H] asialo-orosomucoid at 0 degrees C. As reported previously, the receptor number/cell increases 2-3-fold within 30-60 min when freshly isolated cells are warmed from 0-37 degrees C (Weigel, P. H. (1980) J. Biol. Chem. 255, 6111-6120). This increase in receptor number is not inhibited by cycloheximide and also occurs on cells which have first been treated with EDTA to expose a population of cryptic receptors on the cell surface. The rate and extent of the receptor number increase on the cell surface are proportional to the temperature above about 17 degrees C. If cells are first equilibrated at 37 degrees C and then transferred to a lower temperature, the surface receptor number decreases at a rate and to an extent dependent on the temperature. The surface receptor number can be modulated up and down by successive temperature change cycles between 25 and 37 degrees C. In this temperature range, the number of surface receptors/cell is dependent on the final temperature but independent of the pathway to that temperature and is, therefore, a function of state with respect to temperature. The results demonstrate that temperature changes reversibly modulate the number of receptors on the hepatocyte surface. We conclude that, in the absence of ligand, surface receptors can either recycle or can be reversibly internalized or sequestered to prevent access to ligand. The results may also explain why different laboratories have reported a wide range of values for the number of receptors per hepatocyte. |
