The α1-adrenergic agonist phenylephrine stimulated phospholipase D (PLD) activity in Rat 1 fibroblasts transfected to express either the wild-type hamster α1B-adrenoceptor or a constitutively active mutant (CAM) form of this receptor. The EC50 for agonist stimulation of PLD activity was substantially lower at the CAM receptor than at the wild-type receptor as previously noted for phenylephrine stimulation of phosphoinositidase C activity. Sustained treatment of cells expressing the CAM α1B-adrenoceptor with phentolamine resulted in a marked up-regulation in levels of this receptor with half-maximal effects produced within 24 h and with an EC50 of approx. 40 nM. Such an up-regulation could be produced with a range of other ligands generally viewed as α1-adrenoceptor antagonists but equivalent treatment of cells expressing the wild-type α1B-adrenoceptor was unable to mimic these effects. After sustained treatment of the CAM α1B-adrenoceptor expressing cells with phentolamine, basal PLD activity was increased and phenylephrine was now able to stimulate PLD activity to greater levels than in vehicle-treated CAM α1B-adrenoceptor-expressing cells. The EC50 for phenylephrine stimulation of PLD activity was not altered, however, by phentolamine pretreatment and the associated up-regulation of the receptor. After phentolamine-induced up-regulation of basal PLD activity, a range of α1-antagonists were shown to possess the characteristics of inverse agonists of the CAM α1B-adrenoceptor as they were able to substantially decrease the elevated basal PLD activity.
Up-regulation of the levels of expression and function of a constitutively active mutant of the hamster α1B-adrenoceptor by ligands that act as inverse agonists
- Views Icon Views
- Share Icon Share
- Cite Icon Cite
Tae Weon LEE, Susanna COTECCHIA, Graeme MILLIGAN; Up-regulation of the levels of expression and function of a constitutively active mutant of the hamster α1B-adrenoceptor by ligands that act as inverse agonists. Biochem J 1 August 1997; 325 (3): 733–739. doi: https://doi.org/10.1042/bj3250733
Download citation file: