Muscle cells, glucose uptake into

Defects in glucose uptake into muscle cells are characteristic of insulin resistance in type 2 diabetes and the metabolic syndrome. This phenomenon is likely to be due to reduced activity of a transporter that operates by what mechanism ... 

Insulin stimulates glucose uptake into muscle and adipose cells, at least partly by translocating the glucose transporter (a membrane protein that carries out facilitated diffusion of glucose) from the cytosol (where it resides in the absence of insulin) to the cell surface, in response to insulin. 

In diabetes, glucose uptake into peripheral tissues such as skeletal muscle and fat is impaired, and glucose utilization in the energy-dependent processes within cells is abnormal. The normal uptake and metabolism of glucose in nondiabetic individuals is initiated by a series of intracellular reactions known as the insulin signaling cascade. ... 

Glucocorticoids increase serum glucose levels and thus stimulate insulin release and inhibit the uptake of glucose by muscle cells, while they stimulate hormone sensitive lipase and thus lipolysis. The increased insulin secretion stimulates lipogenesis and to a lesser degree inhibits lipolysis, leading to a net increase in fat deposition combined with increased release of fatty acids and glycerol into the circulation. 

Use of D-fructose by muscle cells is still a matter of debate. The results of in vitro experiments indicate rapid, muscular uptake of D-fructose, with both incorporation into glycogen and oxidation to carbon dioxide. However, when D-glucose is added in increasing amounts to muscle-tissue slices, D-fructose utilization decreases. It follows that metabolism of D-fructose in muscle under normal circumstances is limited, owing to competitive inhibition by D-glucose.73... 

Growth hormone increases the sensitivity of the adipocyte to the lipolytic action of the catecholamines and decreases its sensitivity to the lipogenic action of insulin. These actions lead to the release of free fatty acids and glycerol into the blood to be metabolized by the liver. GH also decreases esterification of fatty acids, thereby reducing triacylglycerol synthesis within the fat cell. Recent evidence suggests that GH may impair glucose uptake by both fat and muscle cells by a postreceptor inhibition of insulin action. 

Glucose transport into muscle cells can be stimulated during exercise because of the activity of the AMP-activated protein kinase Fatty acid uptake into exercising muscle is dependent on the levels of circulating fatty acids, which are increased by epinephrine release. 

The liver is the first organ to receive blood that contains glucose absorbed from the intestine. The portal vein drains from the small intestine into the hepatic sinuses that are surrounded in a neat columnar fashion by hepatocytes. The arrival of glucose in the blood is detected by the p-cells in the pancreas, and they respond by secreting the peptide hormone insulin. Insulin facilitates glucose uptake by many cell types, from skeletal muscle to white blood cells (Fig. 11-4), but it has no effect on glucose uptake by the brain or red blood cells that rely on GLUT-1. 

---