Bacterial swimming strategies and turbulence

Most bacteria in the ocean can be motile. Chemotaxis allows bacteria to detect nutrient gradients, and hence motility is believed to serve as a method of approaching sources of food. This picture is well established in a stagnant environment. In the ocean a shear microenvironment is associated with turbulence. This shear flow prevents clustering of bacteria around local nutrient sources if they swim in the commonly assumed "run-and-tumble" strategy. Recent observations, however, indicate a "back-and-forth" swimming behavior for marine bacteria. In a theoretical study we compare the two bacterial swimming strategies in a realistic ocean environment. The "back-and-forth" strategy is found to enable the bacteria to stay close to a nutrient source even under high shear. Furthermore, rotational diffusion driven by thermal noise can significantly enhance the efficiency of this strategy. The superiority of the "back-and-forth" strategy suggests that bacterial motility has a control function rather than an approach function under turbulent conditions.     

Gender differences in sarcoplasmic reticulum calcium loading after isoproterenol

Males exhibit enhanced myocardial ischemia-reperfusion injury versus females under hypercontractile conditions associated with increased sarcoplasmic reticulum (SR) Ca2+. We therefore examined whether there were gender differences in SR Ca2+. We used NMR Ca2+ indicator 1,2-bis(2-amino-5,6-difluorophenoxy)-ethane-N,N,N',N'-tetraacetic acid to measure SR Ca2+ in perfused rabbit hearts. Isoproterenol increased SR Ca2+ in males from a baseline of 1.13 +/- 0.07 to 1.52 +/- 0.24 mM (P < 0.05). Female hearts had basal SR Ca2+ that was not significantly different from males (1.04 +/- 0.03 mM), and addition of isoproterenol to females resulted in a time-averaged SR Ca2+ (0.97 +/- 0.07 mM) that was significantly less than in males. To confirm this difference, we measured caffeine-induced release of SR Ca2+ with fura-2 in isolated ventricular myocytes. Ca2+ release after caffeine in untreated male myocytes was 377 +/- 41 nM and increased to 650 +/- 55 nM in isoproterenol-treated myocytes (P < 0.05). Ca2+ release after caffeine addition in untreated females was 376 +/- 27 nM and increased to 503 +/- 49 nM with isoproterenol, significantly less than in male myocytes treated with isoproterenol (P < 0.05). Treatment of female myocytes with NG-nitro-l-arginine methyl ester, an inhibitor of nitric oxide synthase (NOS), resulted in higher SR Ca2+ release than that measured in females treated only with isoproterenol and was not significantly different from that measured in males with isoproterenol. Female myocytes also have significantly higher levels of neuronal NOS. This gender difference in SR Ca2+ handling may contribute to reduced ischemia-reperfusion injury observed in females.     

Ephedrine plus caffeine causes age-dependent cardiovascular responses in Fischer 344 rats

Human consumption of ephedrine and caffeine in dietary supplements has been associated with a number of adverse effects including changes in the ECG, myocardial infarction, hyperthermia, and, in rare instances, death. The purpose of this study was to investigate the potential mechanisms associated with the cardiotoxicity of combined ephedrine and caffeine ingestion. Seven- and fourteen-week-old Fischer 344 rats treated with ephedrine in combination with caffeine exhibited increases in heart rate (HR), temperature, and corrected QT interval. Of the 14-wk-old rats treated with 25 mg/kg ephedrine plus 30 mg/kg caffeine, 57% died within 3-5 h of treatment, whereas none of the similarly treated 7-wk-old rats nor any of the rats treated with vehicle died. One hour after treatment with this dose of ephedrine plus caffeine, 14-wk-old rats exhibited a larger increase in HR (as % increase over baseline) than 7-wk-old rats. Furthermore, the 14-wk-old rats that died had a higher HR and temperature than the 14-wk-old rats that lived. Histopathological studies suggested interstitial hemorrhage and myofiber necrosis in the 14-wk-old rats treated with the highest concentration of ephedrine and caffeine. This study showed enhanced susceptibility to ephedrine plus caffeine in 14-wk-old rats compared with 7-wk-old rats. The greater mortality in the 14-wk-old rats was associated with increases in body temperature, HR, and myocardial necrosis.     

The early adaptive evolution of calmodulin

Interaction between gene duplication and natural selection in molecular evolution was investigated utilizing a phylogenetic tree constructed by the parsimony procedure from amino acid sequences of 50 calmodulin- family protein members. The 50 sequences, belonging to seven protein lineages related by gene duplication (calmodulin itself, troponin-C, alkali and regulatory light chains of myosin, parvalbumin, intestinal calcium-binding protein, and glial S-100 phenylalanine-rich protein), came from a wide range of eukaryotic taxa and yielded a denser tree (more branch points within each lineage) than in earlier studies. Evidence obtained from the reconstructed pattern of base substitutions and deletions in these ancestral loci suggests that, during the early history of the family, selection acted as a transforming force on expressed genes among the duplicates to encode molecular sites with new or modified functions. In later stages of descent, however, selection was a conserving force that preserved the structures of many coadapted functional sites. Each branch of the family was found to have a unique average tempo of evolutionary change, apparently regulated through functional constraints. Proteins whose functions dictate multiple interaction with several other macromolecules evolved more slowly than those which display fewer protein-protein and protein-ion interactions, e.g., calmodulin and next troponin-C evolved at the slowest average rates, whereas parvalbumin evolved at the fastest. The history of all lineages, however, appears to be characterized by rapid rates of evolutionary change in earlier periods, followed by slower rates in more recent periods. A particularly sharp contrast between such fast and slow rates is found in the evolution of calmodulin, whose rate of change in earlier eukaryotes was manyfold faster than the average rate over the past 1 billion years. In fact, the amino acid replacements in the nascent calmodulin lineage occurred at residue positions that in extant metazoans are largely invariable, lending further support to the Darwinian hypothesis that natural selection is both a creative and a conserving force in molecular evolution.      

Release of growth hormone from ox pituitary slices after pronase treatment

Proteolytic enzymes have been used both to modify properties of the cell membrane and to dissociate cells from many tissues including pituitary (4, 5, 12). Exposure of secretory tissues to pronase can alter their secretory response. Thus incubation of pancreatic islets of Langerhans in the presence of low concentrations of pronase increased the subsequent release of insulin in the presence of stimulatory and nonstimulatory glucose concentrations (7). The purpose of the present investigation was to determine whether low concentrations of pronase have the same stimulatory effect on the release of a pituitary hormone, growth hormone. Such an effect on hormone release could be of some importance in view of the development of dissociated cell systems as models for the study of the control of hormone release (4, 5).