Cells skeletal muscle

FIGURE 17.11 The structure of a skeletal muscle cell, showing the mauuer iu which t-tubules enable the sarcolemmal membrane to contact the ends of each myofibril iu the muscle fiber. The foot structure is shown iu the box. 

Bradykinin stimulates natriuresis and, through stimulation of prostaglandin synthesis, inhibits the actions of antidiuretic hormone (ADH), thereby inhibiting water retention. Bradykinin further improves insulin sensitivity and cellular glucose utilization of skeletal muscle cells in experimental models. This, however, appears not to be relevant in the clinical context. 

Free fatty acids are removed from the blood extremely rapidly and oxidized (fulfilling 25-50% of energy requirements in starvation) or esterified to form triacylglycerol in the tissues. In starvation, esterified lipids from the circulation or in the tissues are oxidized as well, particularly in heart and skeletal muscle cells, where considerable stores of lipid are to be found. 

The entry rate of glucose into red blood cells is far greater than would be calculated for simple diffusion. Rather, it is an example of facilitated diffiision (Chapter 41). The specific protein involved in this process is called the glucose transporter or glucose permease. Some of its properties are summarized in Table 52-3-The process of entry of glucose into red blood cells is of major importance because it is the major fuel supply for these cells. About seven different but related glucose transporters have been isolated from various tissues unlike the red cell transporter, some of these are insidin-dependent (eg, in muscle and adipose tissue). There is considerable interest in the latter types of transporter because defects in their recruitment from intracellular sites to the surface of skeletal muscle cells may help explain the insulin resistance displayed by patients with type 2 diabetes mellitus. 

In squid giant axons, PbTx causes a depolarization of the plasma membrane, repetitive discharges followed by depression of action potentials, and a complete blockade of excitability. This action is antagonized by TTX (83,84). PbTx depolarizes nerve terminals and induces neurotransmitter release (85,86) it depolarizes skeletal muscle cells (87) and increases the frequency of action potentials in crayfish nerve cord (88). PbTx also produces a contraction of the guinea pig ileum (89). All these effects are prevented by TTX. 

Using the reconstitution approaches described above, we have demonstrated that phosphorylation of the skeletal muscle Ca channels by PKC results in activation of the channels [108], In the fluo 3-containing liposomes, channels phosphorylated by PKC exhibited a two-fold increase in the rate and extent of Ca " influx [108], Using the lipid bilayer-T-tubule membrane reconstitution system we are currently analyzing the effects of PKC-catalyzed phosphorylation at the single channel level [133], The demonstration that these channels undergo phosphorylation as a result of activation of PKC in intact skeletal muscle cells has not yet been achieved. 

Skeletal and cardiac muscles also have important differences. Skeletal muscle cells are elongated and run the length of the entire muscle furthermore, these cells have no electrical communication between them. Cardiac muscle cells, on the other hand, branch and interconnect with each other. Intercellular junctions found where adjoining cells meet end-to-end are referred to as intercalated discs. Two types of cell-to-cell junctions exist within these discs. Desmosomes hold the muscle cells together and provide the structural support needed when the heart beats and exerts a mechanical... 

Genetic Reprogramming of Mammalian Skeletal Muscle Cells by Trichinella spiralis... 

The muscle phase of the infection is initiated by newborn larvae (immature LI larvae). These larvae originate from female worms located in the small intestine of the host. On recognition of skeletal muscle cells, larvae invade and initiate the processes that culminate in long-term intracellular infection of these cells. Following infection, both the parasite and host muscle cell undergo significant changes, over the course of the first 15 days (referred to here as the initiation phase), which is followed by... 

Infection-induced cell cycle re-entry and suspension in G2/M occur early in infection and are likely to influence regulation of some of the other host cell effects (Jasmer, 1993). The earliest indication that 7. spiralis induces terminally differentiated skeletal muscle cells to re-enter the cell cycle came... 

Therefore, it is anticipated that chronic repression of muscle gene expression does not require chronic regulation by the parasite. Rather, this effect is expected to result from chronic suspension of infected cells in a non-Go/Gi gene regulatory environment. A simple hypothesis derived from known characteristics of skeletal muscle cells is that induction of cell cycle re-entry is sufficient to cause both chronic suspension in G2/M and repression of muscle gene expression. This possibility has implications for the number of regulatory points at which the parasite might influence the host cell and possible methods to screen for those products. 

Jasmer, D.P. (1993) Trichinella spiralis infected skeletal muscle cells arrest in G2/M is associated with the loss of muscle gene expression. Journal of Cell Biology 121, 785-793. 

Jasmer, D.P. (1995) Trichinella spiralis subversion of differentiated mammalian skeletal muscle cells. Parasitology Today 11,185-188. 

Blaustein It is not very different from cardiac muscle and some of the early experiments that Gil Wier and others did there. A wave of Ca2+ starts in one place and spreads through the rest of the cell. To try to dump Ca2+ uniformly throughout the cell is very unusual. Skeletal muscle cells may be unusual in this regard, because of the structure of the T-tubules and SR. 

S-100 protein (38) is a 20-kDa calcium-binding protein composed of two subunits, S-lOOa and S-IOOP, which are differentially expressed by individual human tissues. For example, S-100(a,a) is found in myocardial and skeletal muscle cells S-100(a,P) is found in glial cells, melanocytes, chondrocytes, and adnexal glands of the skin and S-100(P,P) is found in Schwann cells and Fangerhans cells of the skin (39). There are currently monoclonal antibodies... 

Figure 5.6 Plot of the rate of glucose uptake (i.e. activity of the carrier) against glucose concentration by a skeletal muscle cell. The curve obeys a hyperbolic equation. The is about 5 mM, which is similar for the enzyme glucokinase for glucose when its activity is plotted against the glucose concentration (see Chapter 3).

Sources of TPO include kidney and skeletal muscle cells but it is primarily produced by the liver, from where it is excreted constantly into the blood. This regulatory factor supports the proliferation, differentiation and maturation of megakaryocytes and their progenitors and... 

---