Muscle cell metabolic activity

Recently, also biological oil-based stent coatings were introduced to deliver drugs. Advantages of these coatings are that they are metabolized by the vascular smooth muscle cells without activating inflammatory cells. 

Hypoxia also causes the release of adenosine from cardiac myocytes. Adenosine in a potent dilator of coronary arteries. It has been shown that adenosine activates K xp currents in single coronary artery smooth muscle cells (Dart and Standen, 1993, 1994). Activation of the K xp channel is also involved in the hypoxic vasodilation in the cerebral, renal (Loutzen-hiser and Parker, 1994), skeletal muscle, and cremaster muscle and cheek pouch circulations (see Nelson and Quayle, 1995). Activation of K xp channels in these vascular beds may be a direct consequence of hypoxia on a smooth muscle oxygen sensor, an effect of hypoxia on smooth muscle cell metabolism, or through the release of vasodilator metabolites like adenosine from surrounding tissue, similar to hypoxic coronary vasodilation. 

All these findings suggested that insulin binding is not an artifact but reflects a true physicochemical combination between muscle cells and insulin. This conclusion found further support from experiments made by Stetten with radioactive insulin ( S- and labeled). The use of labeled insulin permitted Stetten to demonstrate that the insulin concentration is much higher within the tissues than in the medium, and the amount of insulin bound per unit mass was found to be the same when the hormone was injected as when it was added to the incubation mixture. After measuring the amount of bound insulin, the investigators could express the metabolic activity due to insulin—namely, glycogen synthesis per unit mass of bound insulin. These studies established that hormonal activity is proportional to the amount of hormone bound to the muscle cell. Hormonal activity was expressed per unit mass for the first time in these experiments. 

Fung and colleagues examined the metabolic conversion of organic nitrates in sub-cellular fractions of bovine coronary artery smooth muscle cells [66, 67]. They found NO-generating capacity to be present in membrane fractions and, with the use of marker enzymes, identified plasma membrane as the primary location. The enzyme involved in bioconversion was not glutathione-S-transferase [68] and differed from those that catalyse activation of organic nitrites [69]. Partial purification [70] established that the molecular sizes of the native enzyme and subunits were approximately 200 kDa and 58 kDa respectively, and that enzymic activity depends on the presence of a free thiol group. 

Studies were also made of mitochondrial physiology. Laird noted that mitochondrial numbers were greater in metabolically active cells like liver (ca. 1000) compared with resting cells like small lymphocytes (<10). Keith Porter linked the extent of cristal surface with the amount of work done by the cell. Muscle mitochondria had significantly more cristae than those from liver. 

Some of the main types of cellular regulation associated with rhythmic behavior are listed in Table III. Regulation of ion channels gives rise to the periodic variation of the membrane potential in nerve and cardiac cells [27, 28 for a recent review of neural rhythms see, for example, Ref. 29]. Regulation of enzyme activity is associated with metabolic oscillations, such as those that occur in glycolysis in yeast and muscle cells. Calcium oscillations originate... 

Because muscle cells are especially rich in terms of phosphorus-containing metabolites (e.g., ATP, ADP, phos-phocreatine, and orthophosphate), nuclear magnetic resonance " has proved to be a valuable noninvasive probe of metabolic changes attending muscle activity. The spectral sensitivity of P is especially high relative to other nuclei, and one can detect cellular concentrations as low as 0.5 mM as well as utilize chemical shift data to define intracellular pH and free magnesium ion concentrations. See also Nuclear Magnetic Resonance Chemical Shift... 

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 ... 

The current state of Ser/Thr phosphorylation of a protein is determined by the relative activity of Ser/Thr-specific protein kinase and protein phosphatase. It is therefore imderstandable that the cell has had to develop special mechanisms to balance the two activities with one another, and, when needed, to allow kinase or phosphatase activity to dominate. One of the best investigated examples of coordinated activity of protein kinases and protein phosphatases is the regulation of glycogen metabolism in skeletal muscle. Glycogen metabolism is an example of how two different signals, namely a cAMP signal and a Ca signal meet in one metabolic pathway and control the activity of one and the same enzyme. 

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