ELECTRICAL AND MECHANICAL CHARACTERISTICS OF A VERY FAST LOBSTER MUSCLE

The remotor muscle of the second antenna of the American lobster is functionally divided into two parts. One part produces slow, powerful contractions and is used for postural control. The other part produces very brief twitches, can follow frequencies over 100/sec without fusion and is probably used for sound production. This great speed is due, in part, to synchronous arrival of nerve impulses at multiple terminals, a very brief membrane electrical response and electrical continuity throughout large volumes of sarcoplasm. Calculations indicate that the very extensive sarcoplasmic reticulum is probably responsible for the rapid decline of tension in this muscle.     

Adeno-associated virus rep protein synthesis during productive infection.

Adeno-associated virus (AAV) Rep proteins mediate viral DNA replication and can regulate expression from AAV genes. We studied the kinetics of synthesis of the four Rep proteins, Rep78, Rep68, Rep52, and Rep40, during infection of human 293 or KB cells with AAV and helper adenovirus by in vivo labeling with [35S]methionine, immunoprecipitation, and immunoblotting analyses. Rep78 and Rep52 were readily detected concomitantly with detection of viral monomer duplex DNA replicating about 10 to 12 h after infection, and Rep68 and Rep40 were detected 2 h later. Rep78 and Rep52 were more abundant than Rep68 and Rep40 owing to a higher synthesis rate throughout the infectious cycle. In some experiments, very low levels of Rep78 could be detected as early as 4 h after infection. The synthesis rates of Rep proteins were maximal between 14 and 24 h and then decreased later after infection. Isotopic pulse-chase experiments showed that each of the Rep proteins was synthesized independently and was stable for at least 15 h. A slower-migrating, modified form of Rep78 was identified late after infection. AAV capsid protein synthesis was detected at 10 to 12 h after infection and also exhibited synthesis kinetics similar to those of the Rep proteins. AAV DNA replication showed at least two clearly defined stages. Bulk duplex replicating DNA accumulation began around 10 to 12 h and reached a maximum level at about 20 h when Rep and capsid protein synthesis was maximal. Progeny single-stranded DNA accumulation began about 12 to 13 h, but most of this DNA accumulated after 24 h when Rep and capsid protein synthesis had decreased.     

Mechanics of bacterial macrofiber initiation.

The twisting and writhing during growth of single-cell filaments of Bacillus subtilis which lead to macrofiber formation was studied in both left- and right-handed forms of strains FJ7 and RHX. Filament bending, touching, and loop formation (folding), followed by winding up into a double-strand fiber, were documented. Subsequent folds that produced multistrandedness were also examined. The rate of loop rotation during winding up was measured for 26 loops from 16 clones. In most cases, the first loop formed turned at a lower rate than those produced by the following cycles of folding. The sequence of folding topologies differed in FJ7 and RHX strains and in left- versus right-handed structures. Right-handed FJ7 routinely gave rise to four-stranded helices at the second fold, whereas left-handed FJ7 and both left-handed and right-handed forms of RHX made structures with predominantly two double-stranded helical regions. Left-handed RHX structures frequently produced second folds within the initial loop itself, resulting in T- or Y-shaped fibers. Sixteen cases in which the initial touch of a filament to itself produced a loop that snapped open before it could wind up into a double-strand fiber were found. The snap motions were used to obtain estimates of the forces generated by helical growth of single filaments and to investigate theoretical models involving the material properties of cell filaments. In general, the mechanical behavior of growing single-cell filaments and fibers consisting of two-, three-, or four-strand helices was similar to that described for larger, mature, multifilament macrofibers. The behavior of multicellular macrofibers can be understood, therefore, in terms of individual cell growth.     

Control of the rate of phosphocreatine resynthesis after exercise in trained and untrained human quadriceps muscles

We examined the effect of differences in exercise intensity on the time constant (t _c) of phosphocreatine (PCr) resynthesis after exercise and the relationships betweent _c and maximal oxygen uptake (VO_2max) in endurance-trained runners (n = 5) and untrained controls (n = 7) (average VO_2max = 66.2 and 52.0 ml · min^–1 · kg^–1, respectively). To measure the metabolism of the quadriceps muscle using phosphorus nuclear magnetic resonance spectroscopy, we developed a device which allowed knee extension exercise inside a magnet. All the subjects performed four types of exercise: light, moderate, severe and exhausting. The end-exercise PCr: [PCr + inorganic phosphate (P_i)] ratio decreased significantly with the increase in the exercise intensity (P < 0.01). Although there was little difference in the end-exercise pH, adenosine diphosphate concentration ([ADP]) and the lowest intracellular pH during recovery between light and moderate exercise, significant changes were found at the two higher intensities (P < 0.01). These changes for runners were smaller than those for the controls (P < 0.05). The _c remained constant after light and moderate exercise and then lengthened in proportion to the increase in intensity (P < 0.05). The runners had a lowert _c at the same PCr and pH than the controls, particularly at the higher intensity (P < 0.05). There was a significant correlation betweent _c and [ADP] in light exercise and betweent _c and both end-exercise PCr and pH in severe and exhausting exercise (P < 0.05). The threshold of changes in pH andt _c was a PCr: (PCr + P_i) ratio of 0.5. There was a significant negative correlation between the VO_2max andt _c after all levels of exercise (P<0.05).However, in the controls a significant correlation was found in only light and moderate exercise (P < 0.05). These findings suggest the validity of the use oft _c at an end-exercise PCr:(PCr + P_i) ratio of more than 0.5 as a stable index of muscle oxidative capacity and the correlation between local and general aerobic capacity. Moreover, endurance-trained runners are characterized by the faster PCr resynthesis at the same PCr and intracellular pH.     

Reduction of REM sleep by a tryptophan-free amino acid diet.

The acute administration of a tryptophan-free amino acid diet to rats has previously been reported to produce a marked reduction in brain serotonin concentrations. The present study examined the effects of such a diet on electroencephalographic sleep measures. There was a decrease in REM sleep and a small increase in nonREM sleep, with no change in total sleep time. In view of these and other observations, the hypothesis that the serotonergic system plays an important role in the maintenance of nonREM sleep should be carefully reevaluated.     

Treatment of chronic radiation injury over the shoulder with a latissimus dorsi myocutaneous flap.

We report our experiences in treating chronic radiation injury about the shoulder, a complication of radiation after mastectomy. Left untreated, these can result in chronic infection and/or amputation. The coverage of a large shoulder area presents certain unique problems, which severely limit the usefulness of traditional procedures. We have found that the remarkable size and versatility of the latissimus dorsi myocutaneous flap enables one to use it with relative simplicity and safety. A further great advantage is that it brings new permanent blood supply into this ischemic area, thus favoring rapid healing and durable coverage.     

Regulation of expression of the genes encoding steroidogenic enzymes

In recent years it has become apparent that tropic hormones involved in steroidogenesis act to regulate the expression of the enzymes involved in the various steroidogenic pathways. This is particularly evident in the ovary where the episodic secretion of steroids throughout the ovarian cycle is regulated largely by changes in the levels of the particular enzymes involved in each step of the steroid biosynthetic pathways. Recently, the genes for the various cytochrome P450 species involved in ovarian steroidogenesis, namely cholesterol side-chain cleavage P450 (P450SCC), 17 alpha-hydroxylase P450 (P450(17 alpha], and aromatase cytochrome P450 (P450AROM) have been isolated and characterized, making it possible to study the regulation of expression at the molecular level. To this end, a series of chimeric constructs have been prepared in which fragments of the 5'-untranslated region of bovine P450(17 alpha) and P450SCC have been inserted upstream of the chloramphenicol acetyl transferase (CAT) and beta-globin reporter genes. These constructs have been used to transfect primary cultures of bovine luteal and thecal cells. The results indicate that cAMP responsiveness lies within defined regions of genes which do not contain a classical CRE, similar to previous results utilizing adrenal cells in culture. Furthermore, although constructs containing both the P450(17 alpha) and P450SCC 5'-upstream regions are expressed in both luteal and thecal cell cultures, only those containing the P450SCC sequences are expressed in luteal cells. Studies on the expression of P450AROM indicate that the promoter which is responsible for its expression in human placenta is not operative in the corpus luteum. Thus estrogen biosynthesis may be regulated by the differential use of tissue specific promoters, thus accounting for the complexity and multifactorial nature of the expression of this activity.     

Model building of DNA/RNA triple helix containing L-deoxyadenosine.

A three-dimensional model of DNA/RNA triple helix that contains a poly(L-deoxyadenosine) (L-dA) chain is proposed based on computer-assisted model building and energy calculations. The model building was performed by a new method that systematically searches possible conformations of nucleotide units in the helical chains. Two possible orientations of sugar-phosphate chains, in which two homopyrimidine strands are parallel or antiparallel with each other, were considered in the systematic search. Several possible base-pairing models, in which there are one Watson-Crick base pair and one other base pair, were also considered. Many possible models selected by the systematic search were further refined through molecular mechanics calculation incorporating a helical boundary condition. The preferred model, which was selected on the basis of potential energy, was the one with Watson-Crick and Hoogsteen base pairs and with its two polypyrimidine chains in the antiparallel orientation. The model can explain the experimental observation that poly(L-dA) forms a stable triple helix with poly(uridylic acid) (U) but not with poly(deoxythymidylic acid) (dT).