Cooling evokes redistribution of α2c-adrenoceptors from golgi to plasma membrane in transfected human embryonic kidney 293 cells

Cold-induced vasoconstriction in cutaneous blood vessels is mediated by increased constrictor activity of vascular alpha (2)-adrenoceptors (alpha (2)-ARs). In mouse cutaneous arteries, alpha (2)-AR constriction at 37 degreesC is mediated by alpha (2A)-ARs, whereas after cold exposure (28 degreesC), alpha (2C)-ARs are no longer silent and mediate the remarkable cold-induced augmentation of alpha (2)-AR responsiveness. The goals of the present study were to develop a cell model of cutaneous thermoregulation and to determine the mechanisms underlying the thermosensitivity of alpha (2C)-ARs. Human embryonic kidney 293 cells were transiently transfected with the mouse alpha (2A)- or alpha (2C)-AR. In cells expressing alpha (2A)-ARs, UK-14,304 (5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine), an a2-AR agonist, inhibited (10 pM) and stimulated (1-10 nM) the accumulation of cAMP evoked by forskolin. Similar responses were obtained at 37 degreesC and 28 degreesC. In contrast, in cells expressing alpha (2C)-ARs, UK-1 4,304 did not affect forskolin-stimulated cAMP accumulation at 37 degreesC but did cause a concentration-dependent inhibitory effect at 28 degreesC. Subcellular fractionation revealed that at 37 degreesC alpha (2C)-ARs were localized predominantly to Golgi compartments, whereas alpha (2A)-ARs localized predominantly to the plasma membrane. After cooling (28 degreesC), alpha (2C)-ARs relocated from Golgi compartments to the plasma membrane, whereas the alpha (2A)-AR remained at the plasma membrane. Immunofluorescence microscopy confirmed that, at 37 degreesC, alpha (2A)-ARs were localized to the cell surface, whereas alpha (2C)-ARs colocalized with a trans-Golgi marker. Cooling did not affect localization of alpha (2A)-ARs, but shifted alpha (2C)Rs to the cell surface. Moderate cooling, therefore, caused a selective redistribution of alpha (2C)-ARs from the Golgi compartments to the cell surface, allowing the rescue of the alpha (2C)-adrenergic functional response. This mechanism may explain the role of alpha (2)-ARs in thermoregulation of the cutaneous circulation.