Subcellular localization of G-proteins in primary-cultured mouse preadipocytes and adipocytes.

The subcellular localization of G5 alpha, Gi alpha 1&2, Gi alpha 3, and G beta was studied in primary-cultured undifferentiated and differentiated, lipid replete, adipose cells. The results show a distinct distribution for each of these G-proteins and differences between differentiated and undifferentiated cells. All the G-proteins examined had a cytoplasmic localization; only Gi alpha 1 and 2 showed a significant colocalization with the plasma membrane and this only in differentiated cells.

Comparison of the subcellular distribution of G-proteins in hepatocytes in situ and in primary cultures.

The subcellular localization of the heterotrimeric G-proteins in hepatocytes in situ was compared to that in hepatocytes in primary culture. The ability of various ligands to activate adenylyl cyclase (AC) in membrane preparations was also investigated. In hepatocytes in situ the G proteins were mainly localized at the plasma membrane while in hepatocytes in culture they were predominantly cytoplasmic.

Glucose, potassium, and CCK-8 induce increases in membrane-associated PKC activity that correspond to increases in [Ca2+]i in islet cells from neonatal rats.

The effects of glucose, K+, and cholecystokinin octapeptide (CCK-8) on intracellular free Ca2+ concentration ([Ca2+]i) and membrane-associated protein kinase C (PKC) activity were examined in cultured islet cells from neonatal rats. Raising the glucose concentration from 2.8 to 22.

Beta-adrenergic receptors and G-proteins in the ob/ob mouse.

The ob/ob mouse white epididymal adipose tissue is endowed with very low lipolytic activity, due to abnormally low adenylyl cyclase activation in response to beta-adrenergic agents. The abundance of the two principal G-proteins that are responsible for the transduction of adenylyl cyclase is also decreased in several tissues of the ob/ob mouse, compared to levels in the lean mouse. By contrast, beta-adrenergic receptor levels appear normal in adipose tissue (Am J Physiol 1992; 263: C121-C129) and are elevated in liver (Am J Physiol 1994; 265: C1664-C1672), suggesting that the diminished abundance of G-proteins was responsible for the low lipolytic activity.

Of mice and women: the beta 3-adrenergic receptor leptin and obesity.

The metabolic response of adipose tissue to stimuli leading to lipid mobilization is important in determining the direction of metabolism and the degree to which adipose tissue can store lipids and release fatty acids in times of need. The lipolytic machinery is controlled by the activity of hormone-sensitive lipase, which in turn is controlled by the cellular levels of cAMP. The production of cAMP is abnormal in the adipose tissue of some animal models of obesity.