Muscle species differences

NO donors, which release NO or related NO species, are used to elicit smooth muscle relaxation. Different classes of NO donors have differing biologic properties, related to the nature of the NO species that is released and the mechanism that relates to their release. 

Toxicokinetics Absorption of DCA is rapid from the intestinal tract into the bloodstream. Once in the bloodstream, DCA is distributed to the liver and muscles, and then in smaller quantities to the fat, kidney, and other tissues such as the brain and testes. The systemic clearance of DCA is significantly higher. The metabolism of DCA is mediated by a novel CST, CST-zeta found in cytosolic fraction. This enzyme appears to be subjected to autoinhibition by DCA. Although there are substantial species differences in the metabolism of DCA, autoinhibition seems to be true across the species including humans. The half-life of DCA in dogs and rats are between... 

G-actin is very highly conserved, both across actin genes within a species and across species. Apparently, the need for so many functional binding sites in a molecule of that size leaves few options for nonlethal mutations. Among the actins sequenced from 30 widely divergent species, there were only 32 amino acid substitutions. One implication of this is that when differences in contractile properties are observed between various types of muscle, those differences must be due to the motor protein (myosin) or to the various regulatory proteins. 

From his data on four kinds of fish, Dyer (21,22) suggested that fatty fishes are more stable in frozen storage than lean fishes. However, more recent data indicate that species differences may sometimes be more important than fat content (2,43,44). For example, the pattern of ice crystal formation differs between Alaska pollack and yellowtail muscles (34) and this may influence stability. 

The enzymes have molecular weights ranging from about 47 kDa (mouse and rhesus monkey) to 65 kDa (human), and can be found in liver, kidney, small intestine, heart, muscle, lung and other respiratory tissues, adipose tissue, CNS, and blood. Within the blood, CES have been found both in plasma as well as within leukocytes. Species differences in their presence in neuronal tissue and capillary endothelial cells of the CNS have led to some equivocation about their contribution to the blood—brain barrier. That is, the extent to which these enzymes might limit access of drugs into the brain by hydrolyzing them before they can diffuse from the blood into the brain isn t aU that clear. CES are localized both in the cytosol, endoplasmic reticulum (ER), and in lysosomes. 

Using the monoclonal antibody to the 58-kDa fragment, it was found, by Western blots, that a protein similar or identical to the 130-kDa subunit was present in a wide range of tissues (Okubo et al., 1994). A crossreacting species was present in each of the smooth muscles examined (stomach, gizzard, aorta, oviduct, and small intestine) and was also detected in brain, spleen, kidney, lung, and cardiac muscle. Slightly different apparent molecular masses were observed in many tissues, for example, in cardiac muscle a doublet of 143 and 137 kDa was observed. It is not known if these different immunoreactive species are different isoforms. Northern blots confirmed these data, and... 

Although it is less likely, cross-species differences in tissue distribution of isoenzymes could also potentially limit use of CK and LD injury (O Brien et al. 1997a). The distribution of tissue LDH isozymes differs with the various species of laboratory animals. For example, release of liver LDl and LD2 may occur with hepatopathy in some species (e.g., demonstrated in pigs, horses, bovines) and could confound interpretation of increases in blood LD. Similarly, interpretation of increased blood CK may be confounded by release of CK-MB by injury to other tissues such as slow-twitch skeletal muscle, nervous tissue, and uterine smooth muscle (e.g., parturition). Hemolysis could also potentially cause mild increases in these enzymes in certain species. 

Leukotriene Actions in the Gastrointestinal System - Large species differences have been found in the response of gastrointestinal tissue to sulfidcpeptide leukotrienes. Human gastrointestinal muscle (ileum, stonach, jejunum, colon) does not contract to SRS-A from guinea pig lung. In contrast, both LTC, and ITD contract the rat stomach and colon but not the duodenum or ileum. 4 dd E, produce... 

Fig. (6). Effect of grandiflorenic acid (A) and its methyl ester (B) on the uterine smooth muscle of different animal species. C=guinea pig, R=rat and H=human. Details see paper [34],...

Drastic species differences in the subtypes of Ca channels expressed by different cell types have been found. For instance, the K -evoked Ca entry in brain cortex synaptosomes is controlled by N channels in the chick and by P channels in the rat [93], On the other hand, neurotransmitter release at the muscle end plate is controlled by N channels in fish [94-96] and amphibians [97] and by P channels in mammals [98]. 

Prostaglandins of the F and D type generally contract both types of muscle, however, both regional and species differences occur [157,158],... 

Apart from such inter-species differences, many differences have been found in the proportions of enzymes in the different tissues of a single organism, even such very closely related tissues as heart and skeletal muscle. Table 4.3 provides examples. 

There are some points regarding vitamin E supplementation of meat-producing animals that deserve special note. These include the recognition that muscle is among the slowest of tissues to accumulate tocopherol the extent to which tocopherol accumulation differs between muscles within a carcass and that incorporation within a given muscle can differ substantially even between closely related species. 

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