Search PubMed⌕ Search

Biomedical subjects

M Eberhard

Publications and source records attributed to M Eberhard.

31 records · Page 2Linked to original sources
PubMed1991

Calcium binding to fluorescent calcium indicators: calcium green, calcium orange and calcium crimson.

The recently introduced fluorescent calcium sensitive indicators calcium green, calcium orange and calcium crimson suggest important improvements and advantages to detect small calcium transients at low indicator concentrations. Thermodynamic dissociation constants and dissociation rate constants of calcium green, calcium orange and calcium crimson were measured by use of fluorescence titration and stopped flow fluorescence, respectively. Calcium binding to the indicators conforms to a 1:1 calcium:indicator complex although at high concentrations of calcium the fluorescence properties deviate somewhat from the behaviour predicted by the simple model. Dissociation of the calcium-indicator complex was found to be monoexponential under all conditions examined. The affinity for calcium of the three indicators generally increases with raising temperatures (Kd at 11.5 degrees C and 39.7 degrees C (nM): 261, 180 for calcium green; 527, 323 for calcium orange; 261, 204 for calcium crimson) and pH (Kd at pH 6.42 and 7.40 (nM): 314, 226 for calcium green; 562, 457 for calcium orange; 571, 269 for calcium crimson). The changes of the thermodynamic dissociation constant are mainly caused by changes of the association rate constant. The temperature dependence of calcium binding to the indicators revealed that this process is entropically favoured at ambient temperature.

Calcium↗
PubMed1990

A set of programs for analysis of kinetic and equilibrium data.

A program package that can be used for analysis of a wide range of kinetic and equilibrium data is described. The four programs were written in Turbo Pascal and run on PC, XT, AT and compatibles. The first of the programs allows the user to fit data with 16 predefined and one user-defined function, using two different non-linear least-squares procedures. Two additional programs are used to test both the evaluation of model functions and the least-squares fits. One of these programs uses two simple procedures to generate a Gaussian-distributed random variable that is used to simulate the experimental error of measurements. The last program simulates kinetics described by differential equations that cannot be solved analytically, using numerical integration. This program helps the user to judge the validity of steady-state assumptions or treatment of kinetic measurements as relaxations.

Algorithms↗
PubMed1989

Kinetics of calcium binding to fluo-3 determined by stopped-flow fluorescence.

The kinetics of Ca2+ dissociation from fluo-3 was measured using stopped flow fluorimetry. Analysis of dissociation revealed, in contrast to other commonly used fluorescent Ca2+ indicators, a biexponential behaviour with two distinct dissociation rates of 550 s-1 and 200 s-1 at physiological pH and room temperature. The dissociation rate constant of the fast phase increases to 700 s-1 at physiological temperature, whereas that of the slow phase does not change markedly. While the rate constants do not depend on pH between 6.6 and 7.8, the dissociation turns out to be monoexponential at pH 5.86. The association rate of Ca2+ to fluo-3 could not be measured within the mixing dead time and is estimated to be above 10(9) M-1 s-1. Since the rate constants of fluo-3 are larger than those of other fluorescent Ca2+ indicators, fluo-3 is well suited for investigations of Ca2+ oscillations in biological systems.

Aniline Compounds↗
PubMed1989

Modification of a catalytically important residue of indoleglycerol-phosphate synthase from Escherichia coli.

The active-site residues of indoleglycerol-phosphate synthase from Escherichia coli were tentatively localized by comparing crystallographic data with the amino acid identities among the known indoleglycerol-phosphate synthase sequences. To test the validity of the resulting model of catalysis one of the residues in the presumptive active site, Lys 55, was changed to serine using oligonucleotide-directed mutagenesis. The specificity constant kcat/Km of the mutant is 3 x 10(4)-times lower than that of the wild-type enzyme, due to a 60-fold decrease in kcat and a 450-fold increase in Km. This finding shows that Lys 55 is important for both catalysis and substrate binding.

Amino Acid Sequence↗
PubMed1989

Effect of praziquantel on the eggs of Schistosoma mansoni, with a note on the implications for managing central nervous system schistosomiasis.

The morphology of Schistosoma mansoni eggs in intestinal tissues (oograms), and egg hatching in faeces, were studied after parenteral administration of praziquantel (PZQ) to infected mice. PZQ was given parentally in doses of 60 mg kg-1 for one day, five days or 10 days. Eleven days after initiation of therapy, oograms from all groups receiving PZQ showed more dead eggs than controls; a dose response was also observed. Depression of faecal egg hatching occurred within 24 hours of PZQ administration. Our observations suggest that PZQ kills most S. mansoni eggs in host tissues when administered in higher doses than are routinely recommended for treatment of intestinal schistosomiasis mansoni. In order to reduce the lifespan of metabolically active eggs in sensitive tissues, prolonged courses of PZQ could be used when treating central nervous system schistosomiasis.

Animals↗
PubMed1986

Trypanosoma cruzi and Trypanosoma rangeli in Saimiri sciureus from Bolivia and Saguinus mistax from Brazil.

Examination of blood films for trypanosomes in primates housed at the Tulane University Delta Regional Primate Research Center showed that 47% (32/68) of the Bolivian Saimiri sciureus and 51% (68/135) of Brazilian Saguinus mistax harbored one or more types: Trypanosoma (Schizotrypanum) cruzi in 6% to 7% and Trypanosoma (Herpetosoma) spp. or Trypanosoma (Megatrypanum) spp. in 39% and 45%, respectively. Trypanosomes were isolated from a sample of the infected monkeys and morphobiological studies were carried out. Both T. cruzi and Trypanosoma rangeli were demonstrated. The transmission of T. rangeli by Rhodnius prolixus, Rhodnius neglectus, and Triatoma infestans was assessed: only R. prolixus transmitted the infection by bite. T. rangeli has not been found previously in Bolivia, nor has any trypanosome been reported previously in Saguinus mistax.

Animals↗
PubMed1982

Congenital Trypanosoma cruzi infection in a laboratory-born squirrel monkey, Saimiri sciureus.

A Colombian Phenotype, laboratory-born squirrel monkey, Saimiri sciureus, was found to be congenitally infected with biologically proven Trypanosoma cruzi. The parasite was observed in blood smears and by xenodiagnoses of the mother and the offspring, and the isolates produced infection in mice and amastigotes in VERO tissue culture cells. The finding was accidental; both animals were healthy. Tissues of the mother did not show macro-microscopic evidence of T. cruzi infection and the electrocardiograph of the offspring was normal. This seems to be the first report of congenital T. cruzi transmission in an otherwise healthy non-human primate.

Animals↗
PubMed1982

Development of Tetrapetalonema llewellyni to the infective stage in Culicoides hollensis.

The vector requirements and course of larval development for tetrapetalonema llewellyni Price, 1962, a common filaria of raccoons in Louisiana, are described for the first time. Development (from microfilaria to infective stage) took place in the thoracic muscles of the biting midge, Culicoides hollensis (Melander and Brues, 1902) Foote and Pratt, 1954, and required 9 days under laboratory conditions. The findings of this study suggest that species of Culicoides may serve as natural vectors of T. llewellyni.

Animals↗
PubMedDate not supplied

Regulation of inositol 1,4,5-trisphosphate-induced calcium release by inositol 1,4,5-trisphosphate and calcium in human platelets.

Inositol 1,4,5-trisphosphate (IP3)-induced release of Ca2+, its regulation by IP3 and Ca2+, and the metabolism of IP3 was analyzed in saponin-permeabilized human platelets. At 37 degrees C successive sub-maximal aliquots of IP3 induce a biphasic release of part of the IP3-sensitive Ca2+ pool each time. Although the IP3-induced Ca2+ flux rapidly ceases after addition of IP3, the IP3-sensitive Ca2+ stores regain their sensitivity shortly after stimulation with IP3. Under these conditions IP3 is rapidly hydrolyzed to inositol 1,4-bisphosphate which is unable to release Ca2+. The cooperativity of IP3-induced Ca2+ release and the metabolism of IP3 can account for both the rapid recovery of sensitivity of the IP3-sensitive Ca2+ pool and the partial release induced by sub-maximal concentrations of IP3. The data of the present study favour a steady state rather than an all-or-none mechanism of Ca2+ release.

Aniline Compounds↗
PubMedDate not supplied

A specific binding site for angiotensin II(3-8), angiotensin IV, in rabbit cardiac fibroblasts.

This study demonstrates the existence of a high affinity binding site on rabbit cardiac fibroblasts of the hexapeptide (3-8) fragment of angiotensin II (AngIV). [125I]-AngIV binding is saturable, reversible and distinct from angiotensin II (AngII) receptors. At 37 degrees C equilibrium of [125I]-AngIV binding is reached within 2 h. AngIV displaces [125I]-AngIV bound to cultured rabbit cardiac fibroblasts whereas AngII receptor-specific ligands ([Sar1, Ile8]-AngII, Dup753, CGP42112A) do not. Scatchard plot analysis revealed that [125I]-AngIV binds to a single class of sites with Kd = 4.87 +/- 0.11 x 10(-9) mol/l, Bmax = 371 +/- 8.3 fmol/mg protein and a Hill coefficient of 0.92. In the presence of the non-hydrolyzable GTP analog GTPgammaS [125I]-AngIV binding in rabbit cardiac fibroblasts was not markedly affected, whereas binding of [125I]-(Sar1,IIe8)-AngII is reduced. The role of AngIV in the heart and in particular in cardiac fibroblasts is unknown, and the putative interaction of AngIV with AngII needs further characterization.

Amino Acid Sequence↗
PubMedDate not supplied

An increase in hookworm infection temporally associated with ecologic change.

This report describes a significant increase in the prevalence of hookworm infection in an area of Haiti where intestinal parasites are common, but hookworm has not been common. Changing environmental conditions, specifically deforestation and subsequent silting of a local river, have caused periodic flooding with deposition of a layer of sandy loam topsoil and increased soil moisture. We speculate that these conditions, conducive to transmission of the infection, have allowed hookworm to reemerge as an important human pathogen.

Animals↗