The binding of binuclear platinum(II)-terpyridine complexes to DNA.

The binding of platinum (II)-terpyridine complexes to DNA was studied by using equilibrium dialysis. Optical absorption methods were used to measure the ability of the ligands to aggregate in aqueous buffer. Scatchard plots for the binding of the monomeric [Pt(terpy)SC4H9]+ cation to DNA at I0.01 are curvilinear, concave upwards, suggesting two modes of binding. The association constant decreases at higher ionic strengths, consistent with polyelectrolyte theory, and 1.1 cations are released per bound ligand molecule. The association constants of the binuclear ligands [Pt(terpy)S[CH2]4S(terpy)Pt]2+ and [Pt(terpy)S[CH2]6S(terpy)Pt]2+ are 8 and 23 times larger respectively than the affinity of the monomer. For the latter binuclear derivative the increase may be ascribed to bifunctional reaction. Differential dialysis experiments with DNAs of differing base composition show that [Pt(terpy)SC4H9]+ has a requirement for a single G X C base-pair at the highest-affinity site. However, in the binuclear ligands chromophore specificity is severely compromised. Similar experiments indicate that 9-aminoacridine and selected methylene-linked diacridines show no significant sequence selectivity.     

Blast cell activity in mice infected with Hymenolepis nana, H. diminuta and Trichinella spiralis: in vivo uptake of 125IUdR in lymphoid tissues and gut

The kinetics of the lymphoblast response in mice during the course of a primary infection with Hymenolepis nana was measured by the in vivo uptake of 125IUdR. The response was most marked in tissues local to the site of infection, involving the nodes draining the small intestine but not other areas, e.g., inguinal lymph nodes. A close correlation between these responses and the course of infection was observed. Uptake of 125IUdR was greatest in the mesenteric lymph node (MLN) but the peak reached in this organ was later than that in Peyer's patches (PP), small intestine (SI) and spleen (S). The increase in lymphoblast activity of the MLN was similar with Trichinella spiralis; no significant blast cell response to infection with H. diminuta was found till day 9 after injection, the results being similar to those obtained when H. nana infections were established using cysticercoids rather than eggs. It has been shown that the increase in lymphoblast activity was closely correlated with the presence of cells which are most effective in adoptive transfer immunity. A dose-dependent effect was detected in blast cell activity of MLN in different infection levels with T. spiralis and H. nana.     

Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves

A puzzling population-genetic phenomenon widely reported in allozyme surveys of marine bivalves is the occurrence of heterozygote deficits relative to Hardy-Weinberg expectations. Possible explanations for this pattern are categorized with respect to whether the effects should be confined to protein-level assays or are genomically pervasive and expected to be registered in both protein- and DNA-level assays. Anonymous nuclear DNA markers from the American oyster were employed to reexamine the phenomenon. In assays based on the polymerase chain reaction (PCR), two DNA-level processes were encountered that can lead to artifactual genotypic scorings: (a) differential amplification of alleles at a target locus and (b) amplification from multiple paralogous loci. We describe symptoms of these complications and prescribe methods that should generally help to ameliorate them. When artifactual scorings at two anonymous DNA loci in the American oyster were corrected, Hardy-Weinberg deviations registered in preliminary population assays decreased to nonsignificant values. Implications of these findings for the heterozygote-deficit phenomenon in marine bivalves, and for the general development and use of PCR-based assays, are discussed.      

Basolateral plasma membrane localization of ouabain-sensitive sodium transport sites in the secretory epithelium of the avian salt gland

The distribution of Na+ pump sites (Na+-K+-ATPase) in the secretory epithelium of the avian salt gland was demonstrated by freeze-dry autoradiographic analysis of [(3)H] ouabain binding sites. Kinetic studies indicated that near saturation of tissue binding sites occurred when slices of salt glands from salt-stressed ducks were exposed to 2.2 μM ouabain (containing 5 μCi/ml [(3)H]ouabain) for 90 min. Washing with label-free Ringer's solution for 90 min extracted only 10% of the inhibitor, an amount which corresponded to ouabain present in the tissue spaces labeled by [(14)C]insulin. Increasing the KCl concentration of the incubation medium reduced the rate of ouabain binding but not the maximal amount bound. In contrast to the low level of ouabain binding to salt glands of ducks maintained on a freshwater regimen, exposure to a salt water diet led to a more than threefold increase in binding within 9-11 days. This increase paralleled the similar increment in Na+-K+-ATPase activity described previously. [(3)H]ouabain binding sites were localized autoradiographically to the folded basolateral plasma membrane of the principal secretory cells. The luminal surfaces of these cells were unlabeled. Mitotically active peripheral cells were also unlabeled. The cell-specific pattern of [(3)H]ouabain binding to principal secretory cells and the membrane-specific localization of binding sites to the nonluminal surfaces of these cells were identical to the distribution of Na+-K+-ATPase as reflected by the cytochemical localization of ouabain-sensitive and K+-dependent nitrophenyl phosphatase activity. The relationship between the nonluminal localization of Na+-K+-ATPase and the possible role of the enzyme n NaCl secretion is considered in the light of physiological data on electrolyte transport in salt glands and other secretory epithelia.     

Electrostatic components of drug-receptor recognition. I. Structural and sequence analogues of DNA polynucleotides

The electrostatic fields associated with the important biological receptor DNA have been studied by means of stereoscopic displays to investigate drug-receptor recognition processes. This revealed great differences between A- and B-type structures and enabled significant nucleotide sequence effects to be detected for the latter helix. These variations were further investigated by topological analysis of the surface potential in the two grooves of the B-DNA duplex at different radii from the helix axis. This made it possible to characterize the potential surface and to allocate curvature changes to specific atomic groupings. A general finding was that larger potential fields were found in the space encompassed by the narrow groove with strong potential gradients from the ends of the helix to the centre in both grooves. This gradient may provide a motive force for translating small molecules on the surface of a polynucleotide.     

Susceptibility of adult Heligmosomoides polygyrus to intestinal inflammatory responses induced by heterologous infection.

Adult H. polygyrus are capable of surviving for many months after primary exposure of mice to infective larvae, raising the possibility that worms of this species have inherent resistance to intestinal immune responses. Accordingly experiments were carried out to determine whether H. polygyrus are resistant to the inflammatory changes elicited during the acute phase of the intestinal response to Trichinella spiralis. Adult worms were expelled from mice when their presence coincided with the most intense phase of inflammation elicited by T. spiralis. The effect was dose-dependent with more intense T. spiralis challenge resulting in a correspondingly greater loss of H. polygyrus. Even the less pathogenic species T. pseudospiralis elicited a response of sufficient intensity in NIH mice to cause the expulsion of H. polygyrus from concurrently infected animals. Tissue larval stages of H. polygyrus were protected from expulsion by their location deep in the intestinal walls and the maximum detrimental effect against H. polygyrus was observed during the adult phase or during the establishment of L3 larvae. Acceleration of the response to T. spiralis in immune challenged mice resulted in earlier loss of H. polygyrus. When the expulsion of T. spiralis was delayed (e.g. from slow responder C57BL/10 mice) the loss of H. polygyrus took place correspondingly later. These experiments demonstrate unequivocally that mouse strains which normally tolerate chronic infections with H. polygyrus have the capacity to mount intestinal inflammatory responses of sufficient vigour to remove the worms but that this potential is not normally realized. However, the observation that some H. polygyrus always survived even when the response induced by T. spiralis was of the rapid secondary type suggests that the parasites are resilient in the face of the inflammatory response capable of removing most of the worms. It is suggested that in addition to the immunomodulatory strategy employed by adult worms to prevent the intestinal response being elicited, the worms have a second line of defence which is reflected in their resilience to responses which they have been unable to prevent.     

Eimeria vermiformis: differences in the course of primary infection can be correlated with lymphocyte responsiveness in the BALB/c and C57BL/6 mouse, Mus musculus

BALB/c and C57BL/6 mice are high- and low-responders, respectively, to infection with Eimeria vermiformis, this genetically determined difference being immunologically mediated. In order to identify the level at which response phenotype is determined, the proliferation of mesenteric lymph node cells and their ability to transfer immunity adoptively were investigated in each strain; the development of circulating serum antibodies to E. vermiformis was also determined. In all respects BALB/c mice responded earlier than the C57BL/6 but peak values were similar in both strains. The relationship between the temporal differences noted and the characteristic, differing course of the primary infection in the two strains is discussed.