S-Potentials in the Skate Retina : Intracellular recordings during light and dark adaptation

The S-potentials recorded intracellularly from the all-rod retina of the skate probably arise from the large horizontal cells situated directly below the layer of receptors. These cells hyperpolarize in response to light, irrespective of stimulus wavelength, and the responses in photopic as well as scotopic conditions were found to be subserved by a single photopigment with λ_max = 500 nm. The process of adaptation was studied by recording simultaneously the threshold responses and membrane potentials of S-units during both light and dark adaptation. The findings indicate that the sensitivity of S-units, whether measured upon steady background fields or in the course of dark adaptation, exhibits changes similar to those demonstrated previously for the ERG b-wave and ganglion cell discharge. However, the membrane potential level of the S-unit and its sensitivity to photic stimulation varied independently for all the adapting conditions tested. It appears, therefore, that visual adaptation in the skate retina occurs before the S-unit is reached, i.e., at the receptors themselves.     

Determination of Melting Sequences in DNA and DNA-Protein Complexes by Difference Spectra

A graphical formula is presented for determining the base ratio of melted DNA. By use of this formula, the composition of sequences which melt in different portions of the melting curves of Clostridium DNA, Escherichia coli DNA, and mouse DNA were determined. As the DNA melts, the per cent of adenine and thymine (AT) in the melted sequences decreases linearly with temperature. The average composition of sequences which melt in a given part of the melting curve is proportional to the base ratio of the DNA. The concentration and average composition of sequences were determined for three parts of the melting curves of the DNA samples, and a frequency distribution curve was constructed. The curve is symmetrical and has a maximum at about 56% AT. The distribution of GC-rich sequences on the E. coli chromosome was estimated by shearing, partially melting, and fractionating the DNA on hydroxylapatite. GC-rich sequences appear to occur every thousand base pairs, and have a maximum length of about 180 base pairs. The graphical formula was applied to the determination of the composition of sequences which melt in different parts of the melting curve of chromatin. Throughout the melting curve, the composition of the melting sequences is about 60% AT, which appears to suggest that relatively long sequences are melting simultaneously. Their melting temperature may be a function of the composition of the protein on different parts of the DNA. The problem of light scattering in DNA-protein and DNA was also investigated. A formula is presented which corrects for light scattering by relating the intensity of the scattered light to the rate of change of absorbance of DNA with wavelength.     

Increased H-2Dd expression following infection by a molecularly cloned ecotropic MuLV

The biological consequences of radiation leukemia virus (RadLV) infection include the stimulation of H-2D^d antigen expression in resistant mouse strains and thymoma induction in susceptible strains. In an effort to understand the genetic basis of these phenomena, the integrated ecotropic RadLV genome has been examined in a number of primary RadLV-induced tumors, as well as thymomas adapted to in vitro passage; considerable heterogeneity was observed. Examination of these polymorphic viral sequences should help define the viral gene(s) involved in the biological effects of RadLV infection; toward this end, integrated RadLV genomes were molecularly cloned and examined. The genomes and their flanking sequence were characterized by restriction enzyme analysis. Three unique viral genomes were obtained which represent four integration sites. The three RadLV genomes are shown to carry polymorphisms of the original tumor. Following DNA transfection, one of the three genomes replicated in and reinfected both mouse thymocytes and fibroblasts, but not mink fibroblasts in vitro. Virus encoded by the other two DNA genomes could not be recovered following transfection into any of the three cell types. One of these two apparently defective retroviruses encodes a truncated p15E molecule, while the other has elongated long terminal repeats (LTRs). The non-defective ecotropic isolate was collected from in vitro tissue culture supernatants, concentrated, and used to infect mice. Thymocytes of infected, resistant mice were shown to express elevated levels of H-2D^d antigen as early as 12 days post infection, a hallmark of RadLV infection. Offprint requests to: G. D. Brown.     

Catecholamine-Sensitive Adenylate Cyclase in the White Perch (Roccus americanus) Retina: Evidence for β-Adrenergic and Dopamine Receptors Linked to Adenylate Cyclase

We have examined the catecholamine-sensitive adenylate cyclase in the retina of the white perch (Roccus americanus). Both dopamine and the beta-adrenergic agonist isoproterenol stimulate cyclic AMP accumulation in this retina, but serotonin, an indoleamine, and phenylephrine, an alpha-adrenergic agonist, had no effect. The stimulation of adenylate cyclase by isoproterenol is more potent and effective than that of dopamine. The effects of dopamine and isoproterenol are mediated via independent dopamine and beta-adrenergic receptors. Haloperidol, a dopamine antagonist, blocks the stimulatory effect of dopamine but not of isoproterenol. Conversely, propranolol, a beta-adrenergic antagonist, blocks the stimulatory effect of isoproterenol but not of dopamine. The effects of dopamine and isoproterenol are not additive. In fractions of purified horizontal cells we found evidence for dopamine receptors linked to adenylate cyclase but did not find evidence for the presence of cyclase coupled beta-adrenergic receptors. The cellular location of the beta-adrenergic receptors is unknown. Our findings demonstrate the existence of both beta-adrenergic and dopamine receptors coupled to adenylate cyclase in the white perch retina. However, we did not find either epinephrine or norepinephrine, endogenous ligands of the beta-receptor, to be present in retinal extracts subjected to HPLC.     

Impact of Chlorine and Heat on the Survival of Hartmannella vermiformis and Subsequent Growth of Legionella pneumophila

Hartmannella vermiformis, a common amoebal inhabitant of potable-water systems, supports intracellular multiplication of Legionella pneumophila and is probably important in the transportation and amplification of legionellae within these systems. To provide a practical guide for decontamination of potable-water systems, we assessed the chlorine and heat resistance of H. vermiformis. H. vermiformis cysts and trophozoites were treated independently with chlorine at concentrations of 2.0 to 10.0 ppm for 30 min and then cocultured with L. pneumophila. Both cysts and trophozoites were sensitive to concentrations between 2.0 and 4.0 ppm and above (trophozoites somewhat more so than cysts), and 10.0 ppm was lethal to both forms. Hartmannellae treated with chlorine up to a concentration of 4.0 ppm supported the growth of legionellae. To determine whether heat would be an effective addendum to chlorine treatment of amoebae, hartmannellae were subjected to temperatures of 55 and 60°C for 30 min and alternatively to 50°C followed by treatment with chlorine at a concentration of 2 ppm. Fewer than 0.05% of the amoebae survived treatment at 55°C, and there were no survivors at 60°C. Pretreatment at 50°C appeared to make hartmannella cysts more susceptible to chlorine but did not further reduce the concentration of trophozoites.     

POPULATION STRUCTURE OF THE BOTTLENOSE DOLPHIN (TURSIOPS TRUNCATUS) AS DETERMINED BY RESTRICTION ENDONUCLEASE ANALYSIS OF MITOCHONDRIAL DNA

Abstract: Restriction fragment length polymorphisms of mitochondrial DNA (mtDNA) were used to test for population subdivision in the bottlenose dolphin (Tursiops truncatus). Atlantic and Pacific dolphin mtDNA samples exhibited distinctly different haplotypes (approximately 2.4% sequence divergence), indicating a lack of gene exchange. Within the Atlantic Ocean, mtDNA samples from the Gulf of Mexico and the Atlantic Coast were also found to be distinct, with a sequence divergence of approximately 0.6%. The Atlantic Coast–Gulf of Mexico dichotomy is consistent with patterns of genetic variation from other marine and coastal organisms from this region, and supports the hypothesized role of bio-geographic events in promoting the divergence of these and other forms. Regional differentiation was identified along the Atlantic Coast, whereas low sequence divergences among haplotypes and consistent haplotype frequencies across populations suggested considerable gene exchange among Gulf of Mexico populations. A highly divergent haplotype found in two individuals from two localities in the Gulf of Mexico is best explained by dispersal from either a distinct offshore Gulf stock or an unsampled Atlantic Coast stock. Additional samples are required to test for the existence of a distinct offshore race and, if it exists, to identify its distribution and contribution to population structure.     

Isodicentric Y chromosome: cytogenetic,molecular and clinical studies and review of the literature

Dicentrics are among the most common structural abnormalities of the human Y chromosome. Predicting the phenotypic consequences of different duplications and deletions of dicentric Y chromosomes is usually complicated by varying degrees of mosaicism (45,X cell lines), which may, in some cases, remain undetected. Molecular studies in patients with dicentric Y chromosomes have been few, and only two studies have attempted to determine the presence of SRY (the putative testis-determining factor gene). We report an 18-year-old female with short stature, amenorrhea, hirsutism, hypoplastic labia minora, and clitoromegaly who has a 45,X/46,X,idic(Y)(p11.32)/47,X,idic(Y)(p11.32),idic(Y) (p11.32) karyotype. Southern analysis using Y-specific probes (Y97, 2D6, 1F5, pY3.4) and polymerase chain reaction (PCR) analysis using primers for ZFY and SRY were positive for all loci tested, indicating that almost all of the Y chromosome was present. Our findings and an extensive review of the literature emphasize the importance of molecular analyses of abnormal Y chromosomes before any general conclusions can be reached concerning the relative effects of the Y-chromosome abnormality and mosaicism on sexual differentiation.     

Resistance to chenodeoxycholic acid (CDCA) treatment in obese patients with gall stones

In most patients with radiolucent gall stones who were given chenodeoxycholic acid (CDCA) in doses of 13-15 mg/kg body weight/day the bile became unsaturated in cholesterol, and their gall stones dissolved. The patients whose stones did not dissolve were significantly heavier and fatter than the responders, which suggested that obese patients might be “resistant” to the effects of CDCA. To test this hypothesis, 32 consecutive patients presenting for medical treatment of gall stones had their ideal body weight (IBW) and estimated body fat mass calculated. The eight most obese and the eight least obese patients were then selected, and their fasting bile lipid responses to CDCA 13-15 mg/kg/day were measured. The very obese patients were also given larger doses, and any changes in bile lipid composition were studied in relation to subsequent gall-stone dissolution.Before treatment the obese patients had a higher mean biliary cholesterol saturation index than the non-obese patients, and this difference was maintained during treatment with the normal dose of CDCA: the bile in the obese patients remained supersaturated while that in the non-obese became unsaturated with cholesterol. When the obese patients were given larger doses of CDCA their bile ultimately became unsaturated in cholesterol. Gall stones dissolved partially or completely in five of the eight non-obese patients after 6-18 months of 13-15 mg CDCA/kg/day, but none of the obese patients showed any response after comparable periods of treatment with this standard dose. With increased doses and unsaturated bile, however, three of the obese patients showed partial gall-stone dissolution after 3-12 months'' treatment and one showed complete gall-stone dissolution after three years'' treatment.These results suggest that when giving CDCA to patients with gall stones, larger than normal doses (some 18-20 mg/kg/day) should be prescribed. Alternatively the lipid composition of the patients'' bile should be monitored by duodenal intubation and the CDCA dose increased until the bile becomes unsaturated in cholesterol.     

Effects of enkephalins on perfusion pressure in isolated hindlimb preparations

A series of studies were conducted to determine the effects of leucine-(leu-) enkephalin and methionine-(met-) enkephalin on perfusion pressure. These experiments utilized isolated perfused femoral arterial preparations in pentobarbital-anesthetized cats. The enkephalins were administered intraarterially into the femoral artery and changes in perfusion pressure recorded. Leu-enkephalin in doses of 1 μg to 320 μg produced significant dose-dependent decreases in perfusion pressure (4.0 ± 1.3% with 1 μg to 19.1 ± 2.1% with 320 μg). Similar declines in perfusion pressure (5.2 ± 2.4% with 1 μg to 21.7 ± 4.1% with 320 μg) were observed following the administration of met-enkephalin. Pretreatment with naloxone (3 mg/kg) antagonized the effects of both enkephalins. Diphenhydramine (2 mg/kg) effectively antagonized the leu-enkephalin elicited decline in perfusion pressure but blocked the effects of met-enkephalin only at lower agonist doses. Propranolol treatment (4 mg/kg) did not alter the pressure responses to either enkephalin. The results of the study show that intraarterially administered enkephalins exert a vasodilatory effect on vasculature in skeletal muscle which may be direct, indirect or both. The differential antagonism of the effects of the two enkephalins suggest that the two opioids act through different receptors or multiple receptors.