| Comments |
Abstract: "Before ligand exposure, about 300,000 high-affinity receptors were detectable per cell, displayed no latency, and co-distributed with conventional plasma membrane markers." P.2157 right column bottom paragraph: "Exposure to EGF [Epidermal Growth Factor] Induces a Rapid Disappearance of Cell Surface EGF Receptors-[Investigators] measured 150,000 receptors per cell in the perfused liver and 300,000 receptors per cell in vitro. At present [they] don't understand the basis for this two-fold difference, but [they] believe, for several reasons, that the increased number found in liver homogenates represents receptors at the plasma membrane and not those in an intracellular pool. First, the binding in naïve cells displays no latency, whereas [they] can detect latent receptors in cells actively endocytosing EGF. Second, all the binding activity in naïve cells migrates on sucrose gradients with conventional plasma membrane markers, not internal membrane markers. Finally, the initial rapid wave of EGF clearance results in the uptake of about 300,000 ligand molecules, suggesting that all the receptors detected in vitro (300,000/cell) are in a functionally equivalent pool or site." |