The lateral mobility of membrane-associated hormone receptors has been proposed to play an important role in signal transduction. Direct measurements, however, have shown that the receptors for insulin, epidermal growth factor and β-adrenergic antagonists exhibit low mobility at physiological temperature. The present study, which represents the first report of lateral mobility of a polypeptide hormone receptor coupled to adenylate cyclase, yielded quite different results. The lateral mobility of the vasopressin renal-type (V2)-receptor was measured in the basal plasma membrane of cells of the LLC-PK1 porcine epithelial line, using the technique of fluorescence microphotolysis (photobleaching) and a rhodamine-labelled analogue of vasopressin. The analogue, 1-deamino[8-lysine(N6-tetramethylrhodamylaminothiocarbonyl)] vasopressin (TR-LVP) was synthesized and shown to have binding properties and biological activities very similar to those of Arg8-vasopressin (AVP). TR-LVP could be used to label specifically the V2-receptor of living LLC-PK1 cells, whereby LLC-PK1 cells incubated with TR-LVP in the presence of a 100-fold excess of AVP, or cells from the LLC-PK1 V2-receptor-deficient line M18 incubated with TR-LVP could be used as controls for non-specific binding. Using optical sectioning, specific receptor mobility could be measured both in the absence and presence of free TR-LVP. The V2-receptor was found to be largely mobile at 37°C: the mobile fraction (f) was ~0.9, and the apparent lateral diffusion coefficient (D) ~3.0 x 10-10 cm2/s. V2-receptor mobility greatly decreased with decreasing temperature: at 10°C f was reduced to ~0.1. Lipid probe mobility demonstrated that receptor immobility at 10°C was not attributable to a temperature-induced phase transition of the plasma membrane lipid bilayer.
|Number of pages||8|
|Journal||The EMBO Journal|
|Publication status||Published - 1 Jan 1989|