Amiloride and its analogs as tools to inhibit Na+ transport via the Na+ channel, the Na+/H+ antiport and the Na+/Ca2+ exchanger

Amiloride analogs inhibit a number of transmembrane Na+ transport systems: 1) the epithelium Na+ channel, 2) the Na+/H+ exchange system and 3) the Na+/Ca2+ exchange system. Structure--activity relationships using amiloride derivatives with selected modification of each of the functional groups of the molecule indicate that the 3 Na+ transporting systems have distinct pharmacological profiles. 5-N Disubstituted derivatives of amiloride, such as ethylisopropylamiloride are the most potent inhibitors of the Na+/H+ exchange system. Conversely, amiloride derivatives that are substituted on the guanidino moiety, such as phenamil, are potent inhibitors of the epithelium Na+ channel. It is thus possible, by using selected amiloride derivatives to inhibit selectively one or another of the Na+ transport systems.     

Codon usage in selected AT-rich bacteria

The relationship between DNA base composition and codon bias in very AT-rich bacteria was analyzed. Five clostridial genes, five mycoplasmal genes and three rickettsial genes constituted the data base. In the genes of these three organisms, the rule for codon bias was very simple: use U or A in the first and third positions of the codon when possible. This was contrasted with the bias found in Bacillus subtilis and Escherichia coli. The rule for Bacillus subtilis was equally straightforward: use all codons without bias. Only in E. coli, amongst the species examined, did the codon bias appear to be a complicated codon 'choice'.     

Biochemical correlates of fatigue. A brief review

Muscle fatigue, defined as a decreased force generating capacity, develops gradually during exercise and is distinct from exhaustion, which occurs when the required force or exercise intensity can no longer be maintained. We have reviewed several biochemical and ionic changes reported to occur in exercising muscle, and analysed the possible effects these changes may have on the electrical and contractile properties of the muscle. There is no evidence that substrate depletion can account for the decreased force generating capacity, but this factor may be important for the rate of energy turnover and be a major determinant for endurance. Increased concentration of inorganic phosphate and hydrogen ions will depress the force generating capacity, but since fatigue can develop gradually without accumulation of these ions they can only be important when aerobic ATP production is insufficient to support the contractions. Evidence is presented showing that a disturbed balance of K+ alone might cause depolarisation block at high stimulation frequencies, but extracellular K+ accumulation does not increase gradually during prolonged dynamic or static exercise, and is therefore not closely related to fatigue. The repeated release of Ca2+ from the sarcoplasmic reticulum (SR) during muscular activity is suggested of Ca2+ by the mitochondria, increasing with stimulation frequency and duration and possibly also deteriorating mitochondrial function. We therefore speculate that decreased Ca2+ availability for release from SR might contribute to a gradual decline in force generating capacity during all types of exercise.     

Immunohistochemical localization of insulin-like growth factor I in the adult rat

Rabbit antisera against native human insulin-like growth factor I (IGF-I; somatomedin C) or a synthetic tetradecapeptide, representing the carboxyterminal amino acids 57-70 of human IGF-I, were used to map immunohistochemically the distribution of IGF-I immunoreactive material in adult rats. Both antisera were specific for IGF-I, as characterized by immunoabsorption, immunoblotting and radioimmunoassay. There was no cross-reactivity to IGF-II, relaxin or pro-insulin; substances having a high degree of structural homology with IGF-I. High IGF-I immunoreactivity was observed in spermatocytes of the testis; in oocytes, granulosa and theca interna cells of the ovary during early stages of follicle development; in some lymphocytes and in reticular cells of lymphoid and hematopoietic organs; in salivary gland duct cells; in the adrenal medulla, the parathyroid gland and the Langerhans' islets. Chondrocytes in the epiphyseal and rib growth plates and at articular surfaces showed strong IGF-I immunoreactivity. Brown but not white fat cells were stained. Nerve cells in the peripheral and autonomic nervous system showed faint to intense IGF-I immunoreactivity. In contrast, neurons and neuroglial cells in the central nervous system were generally negative; motor neurons being an exception. Erythropoietic, thrombocytopoietic and myeloic cells in the bone marrow showed IGF-I immunoreactivity, but only at defined developmental stages. Hepatocytes showed faint IGF-I immunoreactivity, but became more intensely stained after pretreatment with colchicine. The present results suggest that IGF-I is synthetized by cells in several tissues and organs in the adult rat. There was an apparent association between the localization of IGF-I and cell differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Recognition of a genus-wide antigen ofLegionella by a monoclonal antibody

A monoclonal antibody was produced against a cytoplasmic membrane protein that appears to be common to all species of the genusLegionella. The antibody was positive in polyacrylamide gel electrophoresis and Western blotting with extracts of all of 22 species type strains ofLegionella that were tested. The apparent molecular mass of the protein varied from 57.2 to 62.1 kilodaltons for the 23 species type strains ofLegionella. An enzyme-linked immunosorbent assay (ELISA) was developed with the monoclonal antibody to enable rapid screening of clinical and environmental isolates forLegionella. All of 23 species type strains ofLegionella that were tested were strongly positive with the monoclonal antibody in the ELISA. Among 27 other bacterial species and 84 strains that were tested, onlyBordetella ssp. andAcinetobacter lwoffii were cross-reactive in the ELISA. These two cross-reactive species are readily distinguishable fromLegionella by culture characteristics. The monoclonal antibody may also be useful in tests to detect the genus-wide antigen in body fluids of patients with legionellosis.     

Modified inoculum for radiometric susceptibility testing ofMycobacterium tuberculosis

Two-hundred and fifteen isolates ofMycobacterium tuberculosis were evaluated with the BACTEC 460 radiometric method for susceptibility to isoniazid, rifampin, ethambutol, and streptomycin (SM); a revised protocol for inoculum preparation was used. Fresh clinical isolates were subcultured into 7H9 broth and then photometrically adjusted to the equivalent of a 0.5 McFarland standard, one-half the recommended inoculum density. This method produced an overall 98.3% correlation with a conventional agar method. The sensitivity of this procedure was good for all drugs tested except for the lowest concentration of SM (2 g/ml). Specificity was excellent for all drugs tested. After repeat testing, only four discrepancies were found, yielding a 99.8% correlation between the two systems. The time required for susceptibility tests averaged 4.6 days. This method for inoculum preparation effectively minimized the number of susceptibility tests exceeding the threshold value before the fourth day of incubation. This allowed for definite trends of the growth index values to become established before interpretation of results.     

Ultrastructural changes in transverse striated muscles under the influence of space flight factors

The influence of space flight (on the biosatellite "Kosmos-1667") on muscles (diaphragmatic, soleus, gastrocnemius) was studied by electron microscope. Muscles had destructive and atrophic changes. The rate of changes was maximal in m. soleus, minimal in the diaphragmatic m. However, some regeneration was found demonstrating the reversibility of changes.