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Biomedical subjects

J B Fischer

Publications and source records attributed to J B Fischer.

At least 37 records · Page 2Linked to original sources
PubMed1989

Cloning of the cDNA and gene for a human D2 dopamine receptor.

A clone encoding a human D2 dopamine receptor was isolated from a pituitary cDNA library and sequenced. The deduced protein sequence is 96% identical with that of the cloned rat receptor with one major difference: the human receptor contains an additional 29 amino acids in its putative third cytoplasmic loop. Southern blotting demonstrated the presence of only one human D2 receptor gene. Two overlapping phage containing the gene were isolated and characterized. DNA sequence analysis of these clones showed that the coding sequence is interrupted by six introns and that the additional amino acids present in the human pituitary receptor are encoded by a single exon of 87 base pairs. The involvement of this sequence in alternative splicing and its biological significance are discussed.

Amino Acid Sequence↗
PubMed1988

The bombesin receptor is coupled to a guanine nucleotide-binding protein which is insensitive to pertussis and cholera toxins.

The neuropeptide bombesin acts on a variety of target cells to stimulate the processes of secretion and cell proliferation. In this study we determined whether bombesin receptors interact with known guanine nucleotide-binding proteins in four different cell types: GH4C1 pituitary cells, HIT pancreatic islet cells, Swiss 3T3 fibroblasts, and rat brain tissue. Maximal concentrations of nonhydrolyzable GTP analogs decreased agonist binding to bombesin receptors in membranes from all four sources. In GH4C1 and HIT cell membranes GTP analogs inhibited bombesin receptor binding with IC50 values of about 0.1 microM, whereas GDP analogs were approximately 10-fold less potent. In contrast, GMP and the nonhydrolyzable ATP analog adenylyl-imidodiphosphate had no effect at 100 microM. Equilibrium binding experiments in GH4C1 and HIT cell membranes indicated a single class of binding sites with a dissociation constant (Kd) for [125I-Tyr4]bombesin of 24.4 +/- 7.0 pM and a binding capacity of 176 +/- 15 fmol/mg protein. Guanine nucleotides decreased the apparent affinity of the receptors without significantly changing receptor number. Consistent with this observation, guanine nucleotides also increased the rate of ligand dissociation. Pretreatment of GH4C1 or HIT cells with either pertussis toxin (100 ng/ml) or cholera toxin (500 ng/ml) for 18 h did not affect agonist binding to membrane bombesin receptors, its regulation by guanine nucleotides, or bombesin stimulation of hormone release. Although pertussis toxin pretreatment has been reported to block bombesin stimulation of DNA synthesis in Swiss 3T3 cells, it did not alter the binding properties of bombesin receptors in Swiss 3T3 membranes or inhibit the rapid increase in intracellular [Ca2+] produced by bombesin in these cells. In summary, our results indicate that the bombesin receptor interacts with a guanine nucleotide-binding protein which exhibits a different toxin sensitivity from those which regulate adenylate cyclase as well as those which couple some receptors to phospholipases.

Adenylate Cyclase Toxin↗
PubMed1983

Release of norepinephrine from organ-cultured superior cervical ganglia: effects of the norepinephrine uptake inhibitor xylamine.

After preloading with [3H]norepinephrine (NE), organ-cultured superior cervical ganglia released increased amounts of [3H]NE when incubated with depolarizing K+ concentrations, tyramine or amphetamine. K+-induced release was Ca++-dependent, whereas tyramine- and amphetamine-induced release were not. Analysis of the released radioactivity by high-pressure liquid chromatography showed that these releasing stimuli caused primarily an increase in NE release, with little increase in the release of NE metabolites. Incubation with 10 microM xylamine, an irreversible inhibitor of NE uptake, caused a small increase in [3H]NE efflux, but no reduction in the endogenous NE and dopamine levels in superior cervical ganglia. After xylamine treatment, tyramine-induced release was greatly inhibited, whereas release by amphetamine and K+ was not. The neuronal uptake inhibitor desipramine (1 microM), affected K+-, tyramine- and amphetamine-induced release in a manner similar to xylamine. It is concluded that xylamine is a very weak releasing agent in this tissue and that its effects on other release processes are consistent with its action as a NE uptake inhibitor. Amphetamine-induced release appears not to require the NE uptake system for either the uptake of amphetamine, as shown by the accumulation of [3H]amphetamine, or the efflux of NE.

Animals↗
PubMed1983

Xylamine, an irreversible inhibitor of norepinephrine uptake, is transported by this same uptake mechanism in cultured rat superior cervical ganglia.

The accumulation of tritium-labeled xylamine ([3H]XYL), an irreversible inhibitor of neuronal norepinephrine (NE) uptake, was studied in organ-cultured rat superior cervical ganglia (SCG). At concentrations below those which significantly inhibit NE uptake, [3H]XYL accumulation was linear with time for up to 2 hr; at higher concentrations, accumulation slowed within the first 10 min. [3H]XYL accumulation was inhibited by desipramine, cocaine, bretylium and by NE at concentrations similar to those required to inhibit NE uptake. Replacing Na+ with Li+ in the bathing medium also inhibited [3H]XYL accumulation by about 70%. After 2 days of organ culture, SCG [3H]XYL accumulation was increased in parallel with an increase in NE uptake. Reserpine pretreatment of SCG did not affect [3H]XYL accumulation. The hydrolysis product of XYL, xylaminol, was also accumulated by SCG, but its accumulation was not inhibited by desipramine or the absence at Na+. By using trichloroacetic acid precipitation followed by ethanol extractions, about 40% of the accumulated tritium appeared to be irreversibly bound to protein, whereas about 30% appeared to be bound to lipids. We conclude that XYL is accumulated in sympathetic neurons by the NE uptake system and that this accumulation may be necessary in order for XYL to produce its irreversible inhibition of NE uptake.

Animals↗
PubMed1982

Inhibition of [3H]norepinephrine uptake in organ cultured rat superior cervical ganglia by xylamine.

The superior cervical ganglia (SCG) of the rat, when maintained in organ culture, show an increase in [3H]norepinephrine (NE) uptake in the first 2 days and then a leveling off of this activity through 6 days of culture. The [3H]NE uptake in cultured SCG is Na+ - and temperature-dependent and is inhibited by cocaine, desipramine and benztropine with potencies similar to those reported for uptake inhibition into noradrenergic nerve terminals. The preparation also accumulates [3H]dopamine (DA), but, in contrast to NE and DA uptake in the brain, desipramine and benztropine show no specificity for a particular catecholamine, inhibiting both [3H]NE and [3H]DA uptake with potencies similar to those shown for NE uptake in brain. Thus, observed DA uptake and SCG appears to occur mostly via the NE uptake system, not a specific DA uptake system. Xylamine (N-2-chloroethyl-N-ethyl-2-methylbenzylamine) at 10 microM irreversibly inhibits [3H]NE uptake in cultured SCG by 85% in 30 min, uptake being measured after washing away unbound drug. The IC50 for inhibition is about 0.3 microM. When SCG are again cultured after xylamine exposure, [3H]NE uptake recovers after 2 days. This recovery is partially blocked by cycloheximide, indicating that the synthesis of new uptake sites may be involved.

Animals↗
PubMed1980

The effects of xylamine, a nitrogen mustard on [3H]norepinephrine accumulation in rabbit aorta.

Xylamine (N-2-chloroethyl-N-ethyl-2-methylbenzylamine) irreversibly inhibits [3H]norepinephrine accumulation by rabbit aortic rings in vitro. Inhibition is observed when aortic rings are exposed to xylamine, washed and [3H]norepinephrine accumulation is measured in media free of xylamine. This dose-dependent effect, with an I50 of 10(-7) M, is prevented by coincubation of xylamine with the reversible uptake inhibitors cocaine and amphetamine in the incubation bath during exposure of the tissue to xylamine. The action of xylamine is also sodium dependent, since when tissue was exposed to xylamine in sodium-free Krebs' solution, xylamine had no action. Reduction of potassium ion concentration and the presence of ouabain also protected against xylamine inhibition. These results indicate that xylamine action involves interaction with the neuronal uptake system in a manner very similar to norepinephrine.

Animals↗
PubMed1976

Tinea cruris: diagnostic confusion due to isolation of Candida albicans alone.

The diagnostic importance of the isolation of Candida albicans from a skin lesion is often uncertain. In a 68-year-old man from whose lesions only C. albicans was originally isolated Trichophyton rubrum and Epidermophyton floccosum were also isolated when the growth of the yeast was inhibited in a selective medium. The use of this selective medium, casamino acids erythritol albumin agar, ensures the proper interpretation of the significance of the presence of C. albicans in skin lesions.

Aged↗
PubMed1976

The binding of [3H]dolichol by plasma high density lipoproteins.

Radioactive dolichol was rapidly taken up by a plasma protein fraction following the intravenous injection of detergent suspended [3H]dolichol into rats. The half-life of labeled dolichol in the plasma was found to be approx. 13 h. Density gradient centrifugation or gel filtration of samples of human or rat plasma incubated with [3H]dolichol suspensions also showed that the labeled material became associated with the same plasma protein fractions as in the in vivo studies. Evidence was obtained to indicate that dolichol is specifically associated with the high density lipoprotein fraction of plasma. The possible role of high density lipoproteins as a vehicle for dolichol transport and the problems involved in the binding of this long moleculare are discussed.

Animals↗
PubMed1976

Tinea nigra infection in Canada.

The first infection of tinea nigra known to occur in Canada is reported. The infection occurred on the palm of a Canadian boy, 6 years of age, while he was visiting in the Bahamas. Cultural studies identified the causative fungus to be Cladosporium werneckii.

Canada↗
PubMed1976

Occurrence of Trichophyton megninii in Ontario. Identification with a simple cultural procedure.

Five strains of Trichophyton migninii were isolated in Toronto from four people. One patient probably was infected in Toronto since he had not visited the European endemic area. These were the first isolates made in Ontario; a requirement for L-histidine was determined. A cultural differentiation of T. migninii and T. rubrum is described. Attention is directed to the similarity of the metabolism for dextrose in Bromocresol purple milk dextrose agar by T. megninii and T. mentagrophytes which differs from T. rubrum.

Adolescent↗
PubMed1975

The effect of sodium chloride on the growth and morphology of dermatophytes and some other keratolytic fungi.

A study of the influence of various concentrations of NaC1 on 21 species of dermatophytes and other keratolytic fungi was made. Based on the sensitivity of the species to various concentrations of NaC1, it was possible to divide them into five groups. Microsporum ferrugineum and Trichophyton concentricum and T. tonsurans were the most sensitive to NaC1 and were inhibited by 5%. The greatest number of species were inhibited by 12% NaC1. The fungi most tolerant to NaC1 were M. cookei and M. nanum, and T. mentagrophytes, T. schoenleinii, and T. terrestre. These species were inhibited by 15%. NaC1 prevented any variant change in Epidermophyton floccosum, T. mentagrophytes, and M. gypseum, but promoted a change in phenotype in M. audouinii and M. cookei, and T. gallinae. It is suggested that the word "pleomorphism" be replaced by the term sterile albinism. This term refers to that kind of cultural change when there is no evidence of sporulation and the white fluffy mycelium consists of fine sterile hyphae. Sterile albino strains of E. floccosum were induced to form a macroconidia on Sabouraud cycloheximide chloramphenicol gentamicin agar (SCCGA) containing 3-5% NaC1. Also, M. audouinii formed microconidia and macroconidia in velvety growth cultured on SCCGA containing NaC1.

Epidermophyton↗