Role of calcium in the hormonal regulation of liver metabolism

INTRODUCTION . . . .... . . . . . . . . . . . . .. . . . . . . .... . . . .. . . . . . .. . . . . . . .. . . . . . . .. . . . . ..... . . . . .. . . . . .. ... . . 466 GENERAL MECHANISMS OF SHORT-TERM HORMONAL REGULATION OF HEPATIC METABOLISM . . . ... . . . .... . . . . .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467 SHORT-TERM HORMONAL REGULATION IN THE GLYCOLYTICI GLUCONEOGENIC PATHWAy... . ....... .. . .... . . . . .. . . . . . . . . . . . . .... . . . . ..... . . . 468 Regulation at the PyruvatelPhosphoenolpyruvate Substrate Cycle . . . . . . .. . . . . . . . . . . . . .. 468 Regulation at the Fru-6-PIFru-I.6-Pz Substrate Cycle.... . ... . . . . . .. .... . .... .. . ........ . 469 Coordinated Regulation at the Fru-6-PIFru-I.6-Pz and Pyruvatel Phosphoenolpyruvate Substrate Cycles . . .. .. . ... . . . . . . .. . . .. .. . .. .. . ... . . . ..... . 471 StructurelFunction Relationships of Substrate Cycle Enzymes . . ..... . . ...... . . .... . . . . .. 474

Hepatic Gluconeogenesis/Glycolysis: Regulation and Structure/Function Relationships of Substrate Cycle Enzymes

The role of calcium ion as a mediator of the effects of angiotensin II, catecholamines, and vasopressin on the phosphorylation and activity of enzymes in isolated hepatocytes.

Lipids are essential components of all living cells, functioning as an energy store and playing an important role in all biologic membranes. Triacylglycerols, the storage form and most abundant of the glycerolipids, represent a highly concentrated form of energy, yielding twice as many calories per gram as carbohydrate or protein. The phospholipids are amphipathic compounds which, along with cholesterol, are found in membranes where they interact to provide a polar-faced, hydrophobic continuum of critical importance for proper cell structure and function. A major function of lipogenesis is to store (as triacylglycerols) the chemical energy or foodstuffs ingested above the immediate requirements of an organism. Contrary to protein, which is not stored, and to carbohydrate, which can only be stored in limited quantities, the capacity to store triacylglycerols is almost unlimited. The ability to keep large amounts of triacylglycerols on board would not be useful, however, if it were not possible to quickly and efficiently stop diverting foodstuffs into triacylglycerol formation and to quickly and efficiently start utilizing these compounds to provide the energy necessary to synthesize ATP. For this reason, mechanisms have evolved which finely tune the synthesis and degradation of triacylglycerol to the ever changing demand for ATP. In contrast, phospholipid and cholesterol synthesis must be, at least, partially maintained (or their degradation curtailed), even in the face of limited food intake or frank starvation, to provide sufficient quantities of these lipids to fulfill their crucial role in biologic membranes. In rodents the proportion of total body fatty acids synthesized by the liver ranges from 3% (fasted animals) to 50%

John Lewis Foster

Papers

Acute hormonal control of pyruvate kinase and lactate formation in the isolated rat hepatocyte