Abstract
Acute exercise activates the sympathetic nervous system, and catecholamines play a major role in the exercise-promoted lipid mobilization through adrenergic receptors (AR) which are expressed in adipocytes. Of several subtypes of ARs β-AR is coupled with the stimulatory G-protein (Gs), which activates adenylate cyclase, and in turn stimulates lipolysis. The aim of this study was to investigate the effect of acute exercise on β-AR-G-protein system in rat adipocytes. Adipocytes from epididaymal adipose tissue were isolated at 0, 3, and 24 h after acute exercise. Neither protein expression nor mRNA level in several types of Gsα was changed at each time point. However, protein expression of Gi2α which mainly inhibits adenylate cyclase activity decreased at 0 and 3 h, but it significantly increased at 24 h. In contrast, β-AR number increased at 0 and 3 h, but decreased at 24 h. In accordance with these phenomena, isoproterenol-stimulated cAMP productions increased at 0 and 3 h, but decreased at 24 h. Moreover, we investigate possible mechanism behind exercise-induced alterations in Gi2α protein. Proteasome activities were increased at 0 and 3h, but decreased at 24 h. Co-immunoprecipitation of Gi2α with ubiqutin was significantly increased at 0 and 3 h. The injection of lactacystin, a selective proteasome inhibitor, significantly increased Gi2α protein expression at 0 and 3 h compared with the value prior to exercise. These results suggest that ubiquitin-proteasome system regulates protein expressions of Gi2α. [Jpn J Physiol 54 Suppl:S238 (2004)]
