Intercellular communication in rat seminiferous tubules

Intercellular electrical coupling in seminiferous tubules from prepubescent and adult Wistar rats has been studied by using conventional techniques. It is found that cells in the seminiferous epithelium are electrically coupled. Experiments performed using "Sertoli cell-enriched" seminiferous tubules indicate the existence of intercellular ionic communication between Sertoli cells. Junctional conductance is independent of the direction of electrical field and it is affected by A23187 Ca ionophore (5 microM) but not by exposure to the neurotransmitter norepinephrine (1-5 X 10(-5) M). Intracellular resistivity (including junctional resistance) is higher in mature as compared to immature germinal epithelium. These findings suggest that cell metabolites or second messenger molecules could be transferred via the low-resistance pathways between epithelium cells to coordinate cellular activity.     

Salmonella typhimurium infection in high and low antibody responder mice: inverse correlation between antibody responsiveness and resistance to infection

Susceptibility to Salmonella typhimurium infection was compared in H (high Ab responder) and L (low Ab responder) mice obtained by several selective breeding experiments (Selections I, II, III, IV and IV A). H mice were always much more susceptible to infection than their L mice counterparts within a continuous LD 50 variation range. In three of the selections (I, II and IV A) the low responsiveness character is known to result mainly from rapid Ag degradation in L mice macrophages. It was hypothesized that resistance to multiplication of intracellular pathogens could be related to an increased catabolic activity towards Ag. This was actually demonstrated, in F2 segregant hybrids of selection IV A, by the significant inverse correlation between capacity for Ab production and resistance to infection.     

Molecular cloning of a gene encoding a Chlamydia psittaci 57-kDa protein that shares antigenic determinants with ca. 60-kDa proteins present in many Gram-negative bacteria

In order to develop reagents to study the immune response of guinea pigs to infection by Chlamydia psittaci guinea pig inclusion conjunctivitis strain (GPIC), we constructed a plasmid clone bank with C. psittaci DNA. One of the recombinant clones isolated produced large amounts of a 57-kilodalton (kDa) protein that was immunoreactive with sera from GPIC infected guinea pigs. While investigating this recombinant protein, we discovered that all the Gram-negative bacteria analyzed so far have immunoreactive proteins of similar size. This protein seems to be a 'common antigen' already described in various Gram-negative bacteria.     

Influences of root distribution and growth on predicted water uptake and interspecific competition

Summary Root distribution and growth measured in the field were incorporated into a water uptake model for the CAM succulent Agave deserti and its nurse plant Hilaria rigida, a common desert bunchgrass. Agave deserti responds to the infrequent rainfalls of the Sonoran Desert by extending its existing established roots and by producing new roots. Most of such root growth was completed within one month after soil rewetting, total root length of A. deserti increasing by 84% for a seedling and by 58% for a mediumsized plant in the summer. Root growth in the winter with its lower soil temperatures was approximately half as much as in the summer. For a 15-year period, predicted annual root growth of A. deserti varied more than 18-fold because of annual variations in rainfall amount and pattern as well as seasonal variation in soil temperature. Predicted annual water uptake varied 47-fold over the same period. The nurse plant, which is crucial for establishment of A. deserti seedlings, reduced seedling water uptake by 38% during an average rainfall year. Lowering the location of the root system of a medium-sized A. deserti by 0.24 m reduced its simulated annual water uptake by about 25%, reflecting the importance of shallow roots for this desert succulent. Lowering the root system of a medium-sized H. rigida by 0.28 m increased the simulated annual water uptake of an associated A. deserti seedling by 17%, further indicating the influence of root overlap on competition for water.     

Structural analysis of the gene for the beta chain of the antigen-specific receptor of mammalian T-lymphocytes

The antigen specific receptor of T cells (TCR) is composed of alpha and beta chains and is normally present on the T cell surface complexed with the components which make up T3. In the case of beta chain, multiple somatic DNA rearrangements bring together V beta (variable), D beta (diversity) and J beta (joining) gene segments before a mature messenger RNA can be transcribed. So far beta chain genes have been extensively studied in the human and in the mouse system and we have very little information on other mammals. Our aims were to obtain information that may provide a structural basis for understanding developmental as well as evolutionary aspects of the TCR gene system in mammals. In this study we compare the hybridization pattern between a human cDNA probe coding for the beta chain constant region and restricted genomic DNA extracted from lymphocytes deriving from human as well as from rat and lamb. The comparison of the hybridization data represent a first piece of information about the variation of the structure of the TCR beta chain genes in mammals.     

Theoretical study of the acidic strength of amino acid side chains

The acidic strengths in gas phase of three groups (NH₄⁺, H₂S, and HCOOH) that mimic the most common amino acid side chains of enzymes are studied by means of quantum mechanical methods. The results demonstrate that in gas phase the acidities of such groups change drastically with respect to those reported in aqueous phase. Moreover, the dependence between the energetics of the proton-transfer process and the distance separating the acid and base groups is stated. The biological implications of these results are discussed.     

Effect of 17β-estradiol on calcium response to phytohaemagglutinin in human lymphocytes

Pre-treatment of human lymphocytes with 17-estradiol diminishes the increase in concentration of cytosolic free calcium after stimulation with phytohaemagglutinin. The effect is dependent on 17-estradiol concentration and on the preincubation time. The effect is not due to an interaction between 17-estradiol and phytohaemagglutinin, but appears to be a consequence of the binding of the hormone to the cell surface. The effect is specific for 17-estradiol, since the isomer and other steroid hormones (progesterone, testosterone, diethylstilbestrol and 5-androstan), have no effect. Since the effect of the 17-estradiol can be suppressed by treatment of lymphocytes with ouabain, it appears that the effect of estradiol on the rise of cytosolic calcium induced by phytohaemagglutinin is mediated by the (Na, K)-ATPase.