Fine Structure of Rickettsia canada in Tissues of Dermacentor andersoni Stiles

Preliminary observations on growth and developmental fine structure of Rickettsia canada in various organs and tissues of the hard tick, Dermacentor andersoni Stiles, are reported. R. canada is typically rod-shaped, being delimited with a three-layered wall having a velvety coating adsorbed to its exterior surface. A finely reticulated cytoplasmic matrix containing prominent ribosomes is delimited with a three-layered unit membrane. Average length and width of these organisms are 1.6 by 0.4 mum. Although R. canada produces a generalized infection in D. andersoni, hypodermal and muscle tissues experience heaviest growth. Three morphologically distinct rickettsial forms were observed in individual hypodermal cells: (i) typical growth forms with a finely reticulated cytoplasmic matrix and distinct ribosomes; (ii) atypical forms with lightly to densely staining cytoplasm and a coagulated appearance in which ribosomes cannot be distinguished from the matrix; and (iii) forms with crystalline bodies that have a striated to beaded lattice structure and, at times, a fibrillar body in the cytoplasm as well. Occasional finger-like to irregular invaginations of the plasma membrane are noted. Intranuclear growth was demonstrated by electron microscopy in gut epithelial cells only. Growth and development of R. canada were manifest in all tissues examined.     

Relationship between force and intracellular [Ca2+] in tetanized mammalian heart muscle

To determine features of the steady state [Ca2+]-tension relationship in intact heart, we measured steady force and intracellular [Ca2+] ([Ca2+]i) in tetanized ferret papillary muscles. [Ca2+]i was estimated from the luminescence emitted by muscles that had been microinjected with aequorin, a Ca2+-sensitive, bioluminescent protein. We found that by raising extracellular [Ca2+] and/or by exposing muscles to the Ca2+ channel agonist Bay K 8644, tension development could be varied from rest to an apparently saturating level, at which increases in [Ca2+]i produced no further rise in force. 95% of maximal Ca2+-activated force was reached at a [Ca2+]i of 0.85 +/- 0.06 microM (mean +/- SEM; n = 7), which suggests that the sensitivity of the myofilaments to [Ca2+]i is far greater than anticipated from studies of skinned heart preparations (or from previous studies using Ca2+-sensitive microelectrodes in intact heart). Our finding that maximal force was reached by approximately 1 microM also allowed us to calculate that the steady state [Ca2+]i-tension relationship, as it might be observed in intact muscle, should be steep (Hill coefficient of greater than 4), which is consistent with the Hill coefficient estimated from the entire [Ca2+]i-tension relationship derived from families of variably activated tetani (6.08 +/- 0.68; n = 7). Finally, with regard to whether steady state measurements can be applied directly toward understanding physiological contractions, we found that the relation between steady force and [Ca2+]i obtained during tetani was steeper than that between peak force and peak [Ca2+]i observed during physiological twitches.     

Measurements of amino acid transport in internally dialyzed giant axons

Summary It is shown that the axoplasmic composition of acidic and neutral amino acids can be controlled effectively by the method of internal dialysis. Direct assay for specific binding and measurement of diffusion coefficients in axoplasm show that there is no significant binding or compartmentalization of amino acids. The dependence of amino acid efflux on substrate concentration can be measured under well-defined, true steady-state conditions. The taurine efflux-concentration relation in theMyxicola giant axon conforms to a second-order Hill equation. This fact is consistent with either a cooperative process or a mechanism in which membrane translocation is not the rate-controlling step. The effluxes of taurine and glycine from squid axon are an order of magnitude smaller than inMyxicola. The efflux-concentration relations are essentially linear up to 200mm substrate concentration. This result may be produced by specific transporters which have very high asymmetry, or by simple diffusive leak in the absence of specific transporters.     

Heat Inactivation of In Vivo- and In Vitro-Grown Mycobacteria in Meat Products

Heat inactivation of mycobacteria from lesions and from culture was compared in meat products. In vivo-grown organisms were more easily heat inactivated than were in vitro-grown organisms.     

CERTAIN ENZYMATIC ACTIVITIES OF NORMAL AND MOSAIC INFECTED TOBACCO PLANTS

The lower leaves of tobacco plants were inoculated with leaf mosaic virus and the activities of oxygenase, peroxidase, catalase, and invertase were followed in leaves of comparable age at intervals of 2 or 3 days over a period of 21 days. The inoculated leaves exhibited a great decrease relative to normal tissue in the activity of oxygenase and peroxidase on the 6th day. Younger leaves showed this minimum at a progressively later date. A great decrease in the activities of these enzymes was attained by the 14th to the 18th day. This maximum was followed by a decrease. Catalase exhibited an increased activity which reached a maximum at about the 8th day. A second maximum was observed on the 16th to the 18th day. Invertase reached a minimum, relative to normal plants, on about the 8th day. A second minimum was approached on the 16th to the 18th day. These data show that profound disturbances in the physiology of infected plants occur many days before the leaf juice attains an infectious concentration of virus. The observed activities could not be due therefore to metabolic activities of the virus particles themselves. Since infectivity is attained only after a period of profound physiological disturbance, it seems possible that the virus protein develops as a product of abnormal metabolism.     

Calcium uptake by leukemic and normal T-lymphocytes exposed to low frequency magnetic fields

Calcium-ion uptake by normal and leukemia lymphocytes increased during a 30-min exposure to a 13.6 Hz, sinusoidal magnetic field at 20 microT peak. The time-varying field was horizontal and parallel to a 16.5 microT component of the ambient static magnetic field. The uptake of 45Ca2+ increased 102% in a line of murine, cytotoxic T-lymphocytes (C57B1/6-derived CTLL-1), increased 126% in freshly-isolated spleen lymphocytes (C57B1/6 mice), and increased 75% in a line of lymphoma cells (C57B1/6-derived EL4). In contrast, there was no effect when the same field was applied for 30 min immediately before--as opposed to during--incorporation of calcium ions. When spleen lymphocytes were exposed during incubation with 45Ca2+ to a 60 Hz magnetic field at 20 microT peak, a small but statistically significant increase (37%) in uptake of the labeled ions occurred. These results indicate that weak, alternating magnetic fields might affect calcium-dependent functions of normal and leukemic lymphocytes.     

Reproductive Biology and Behavior of Rhabditis pellio, (Schneider) (Rhabditida: Rhabditidae)

Laboratory studies were conducted on the mating behavior of Rhabditis pellio males and females, which were maintained on a culture of Flavobacterium sp. bacteria isolated from earthworms. The mean time that elapsed between first contact of the sexes and their ultimate separation was 23.2 min. However, only 5.0 min were required for copulation (the interval during which male spicules were inserted into the female vagina). Three-day-old females that were permitted to mate once on their first day of adult life produced only one-third as many larvae as did females that were permitted unlimited mating. However, the longevity of females was found to decrease with an increase in the number of matings. Both males and females that were permitted to mate daily produced the greatest number of offspring when they were 4 days old. When the initiation of mating was delayed beyond their third day of life, the number of larvae produced by females decreased. In approximately one-half of the copulations, males failed to inseminate their female partners.