Effect of injected glucagon or fatty acids on mitochondrial ATPase

Hepatic glucagon action: beyond glucose mobilization

Glucagon's ability to promote hepatic glucose production has been known for over a century, with initial observations touting this hormone as a diabetogenic agent. However, glucagon receptor agonism [when balanced with an incretin, including glucagon-like peptide 1 (GLP-1) to dampen glucose excursions] is now being developed as a promising therapeutic target in the treatment of metabolic diseases, like metabolic dysfunction-associated steatotic disease/metabolic dysfunction-associated steatohepatitis (MASLD/MASH), and may also have benefit for obesity and chronic kidney disease. Conventionally regarded as the opposing tag-team partner of the anabolic mediator insulin, glucagon is gradually emerging as more than just a "catabolic hormone." Glucagon action on glucose homeostasis within the liver has been well characterized. However, growing evidence, in part thanks to new and sensitive "omics" technologies, has implicated glucagon as more than just a "glucose liberator." Elucidation of glucagon's capacity to increase fatty acid oxidation while attenuating endogenous lipid synthesis speaks to the dichotomous nature of the hormone. Furthermore, glucagon action is not limited to just glucose homeostasis and lipid metabolism, as traditionally reported. Glucagon plays key regulatory roles in hepatic amino acid and ketone body metabolism, as well as mitochondrial turnover and function, indicating broader glucagon signaling consequences for metabolic homeostasis mediated by the liver. Here we examine the broadening role of glucagon signaling within the hepatocyte and question the current dogma, to appreciate glucagon as more than just that "catabolic hormone."

Glucagon Regulation of Energy Expenditure

Glucagon's ability to increase energy expenditure has been known for more than 60 years, yet the mechanisms underlining glucagon's thermogenic effect still remain largely elusive. Over the last years, significant efforts were directed to unravel the physiological and cellular underpinnings of how glucagon regulates energy expenditure. In this review, we summarize the current knowledge on how glucagon regulates systems metabolism with a special emphasis on its acute and chronic thermogenic effects.

Effect of redox potential on rat liver F1-ATPase

Redox titration of F1-ATPase from rat liver mitochondria referred to the modification of the hydrolytic activity on Mg-ATP has resulted in a three-step pattern, with three distinct jumps of activity separated by clear plateaus. The measured potentials ranged from -400 mV to +400 mV and were obtained by the addition of dithionite and ferricyanide. Electron exchange was facilitated with a mixture of different redox mediators. At pH 7.4 the midpoint potentials were +210 mV, +40 mV and -230 mV. These three midpoint potentials were displaced towards more negative values by 2,4-dinitrophenol or by an increase of the pH of the medium. The titration curves were described by n = 2 Nernst equations.