ATP analogs and muscle contraction: mechanics and kinetics of nucleoside triphosphate binding and hydrolysis

The mechanical behavior of skinned rabbit psoas muscle fiber contractions and in vitro motility of F-actin (Vf) have been examined using ATP, CTP, UTP, or their 2-deoxy forms (collectively designated as nucleotide triphosphates or NTPs) as contractile substrates. Measurements of actin-activated heavy meromyosin (HMM) NTPase, the rates of NTP binding to myosin and actomyosin, NTP-mediated acto-HMM dissociation, and NTP hydrolysis by acto-HMM were made for comparison to the mechanical results. The data suggest a very similar mechanism of acto-HMM NTP hydrolysis. Whereas all NTPs studied support force production and stiffness that vary by a factor 2 or less, the unloaded shortening velocity (Vu) of muscle fibers varies by almost 10-fold. 2-Deoxy ATP (dATP) was unique in that Vu was 30% greater than with ATP. Parallel behavior was observed between Vf and the steady-state maximum actin-activated HMM ATPase rate. Further comparisons suggest that the variation in force correlates with the rate and equilibrium constant for NTP cleavage; the variations in Vu or Vf are related to the rate of cross-bridge dissociation caused by NTP binding or to the rate(s) of product release.     

Comparison of type I and type II Chlamydia psittaci strains infecting koalas (Phascolarctos cinereus)

The native Australian marsupial Phascolarctos cinereus, otherwise known as the koala, is prone to infection by the obligate intracellular parasite Chlamydia psittaci, which causes ocular 'pink eye' and urogenital 'dirty tail' diseases. Several chlamydial DNA probes to both chromosomal and plasmid sequences were used to type by Southern blot analysis 51 samples taken from wild and captive koalas from habitats on the eastern seaboard of Australia as far apart as Queensland and Victoria. Two types of C. psittaci were observed and called types I and II. Type II was found more frequently than type I and occurred in both ocular and urogenital samples, while type I showed a strong but not absolute preference for ocular sites. Cross-hybridization analyses indicated that type I and type II had about 10% DNA sequence identity to each other. DNA analyses showed that type II was very closely related to some ovine and bovine chlamydiae but type I could not be related to any other C. psittaci strain available. Light and electron microscopic analyses of infected BGM monolayers revealed that the two strains were similar in morphological characteristics. The type I strain was considerably more infectious than the type II strain in BGM cells and in the yolk sacs of embryonated eggs. A PCR based assay detected both type I and type II koala chlamydiae in samples that had been negative by Southern blot and tissue culture and provided the first evidence that both types can occur simultaneously at the one site of infection.     

Anesthesia inhibits interferon-induced natural killer cell cytotoxicity via induction of CD8+ suppressor cells

Anesthesia (Avertin, halothane, isoflurane, ether, or ketamine/xylazan) of mice inhibits subsequent stimulation of splenic natural killer cell (NK) cytotoxicity by interferon (IFN) treatment either in vitro and in vivo. The current data demonstrate (a) in vitro depletion of CD8+ cells from mononuclear splenocytes of anesthetized mice restored the ability of NK cells to respond in vitro to IFN stimulation and (b) coincubation of CD8+ splenocytes from anesthetized mice with CD8- splenocytes of naive mice resulted in a significant reduction of the IFN-induced stimulation of NK activity in the coculture. These results suggest that anesthesia induces CD8+ cells that suppress stimulation of NK cytotoxicity by IFN.     

Effect of catching method and lighting intensity on the prevalence of broken bones and on the ease of handling of end-of-lay hens

Five catching methods were compared in terms of their effect on the proportion of battery hens which had bones broken when they were removed from battery cages. In addition the effect of tier, lighting intensity during lay and lighting intensity during handling on the prevalence of fractures at catching and on old fractures which occurred during lay was evaluated. Catching and removing hens by one leg from the cages resulted in 11 to 14 per cent of the birds acquiring a broken bone, whereas catching and removing each bird by two legs resulted in 5 per cent of the birds acquiring a freshly broken bone. Removing more than one bird at a time from the cage tended to cause more skeletal damage than removing them individually, and incorporating a wooden breast support slide over the feed trough had no effect on the prevalence of broken bones. Catching birds in the top tier of a three-tiered battery unit was more difficult than for the middle or bottom tiers. When the light intensity at catching was the same as that during lay birds were more difficult to catch than when the light intensity was changed, but the effects were insufficient to affect the prevalence of damage to the skeleton.     

Effects of quarantine on cats and their owners

The effects of quarantine on 16 cats and their owners were assessed by means of four questionnaires completed by the owners at the beginning of their cat's stay in quarantine, three months later, and two weeks and three months after the cats left quarantine. Changes in body condition were evident in two-thirds of the cats during and at the end of quarantine but not three months later. Mid-way through quarantine, the owners considered their cats were less attached to them, less relaxed, more excitable, more aggressive, more nervous and less playful than before quarantine. When they left quarantine the cats were friendlier, more affectionate and more timid, and three months later they were more affectionate, more nervous and more vocal than before quarantine. When they left quarantine and three months later the cats spent more time with their owners than before quarantine. Most owners visited their cats once or twice a month; the location of the cattery and the limited opening hours restricted the number of visits they made.