Cooling evokes redistribution of alpha(2c)-adrenoceptors from golgi to plasma membrane in transfected human embryonic kidney 293 cells

Cold-induced vasoconstriction in cutaneous blood vessels is mediated by inc reased 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 stud y were to develop a cell model of cutaneous thermoregulation and to determi ne the mechanisms underlying the thermosensitivity of alpha (2C)-ARs. Human embryonic kidney 293 cells were transiently transfected with the mouse alp ha (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 agonis t, inhibited (10 pM) and stimulated (1-10 nM) the accumulation of cAMP evok ed by forskolin. Similar responses were obtained at 37 degreesC and 28 degr eesC. In contrast, in cells expressing alpha (2C)-ARs, UK-1 4,304 did not a ffect forskolin-stimulated cAMP accumulation at 37 degreesC but did cause a concentration-dependent inhibitory effect at 28 degreesC. Subcellular frac tionation revealed that at 37 degreesC alpha (2C)-ARs were localized predom inantly to Golgi compartments, whereas alpha (2A)-ARs localized predominant ly to the plasma membrane. After cooling (28 degreesC), alpha (2C)-ARs relo cated from Golgi compartments to the plasma membrane, whereas the alpha (2A )-AR remained at the plasma membrane. Immunofluorescence microscopy confirm ed 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 redistributio n of alpha (2C)-ARs from the Golgi compartments to the cell surface, allowi ng the rescue of the alpha (2C)-adrenergic functional response. This mechan ism may explain the role of alpha (2)-ARs in thermoregulation of the cutane ous circulation.