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A Auerbach

Publications and source records attributed to A Auerbach.

16 recordsLinked to original sources
PubMed1992

The gene trap approach in embryonic stem cells: the potential for genetic screens in mice.

The gene trap approach in embryonic stem cells was developed as a means to screen for genes expressed during early postimplantation development in the mouse. We have validated the approach by showing that lacZ from the integrated vector is activated by splicing to endogenous exons and expressed in embryos in patterns that mimic those of the endogenous genes. These insertions can produce developmental defects in homozygous mice. The results indicate that a large screen of gene trap cell lines on the basis of embryonic lacZ expression is feasible and should provide a new source of genes, mouse mutants and mouse strains that express lacZ in particular domains and lineages. The gene trap approach could be extended to a smaller screen for genes based on mutant phenotypes.

Amino Acid Sequence↗
PubMed1991

Single-channel dose-response studies in single, cell-attached patches.

A method for carrying out dose-response studies of ion channel currents in cell-attached patches has been devised. Patch pipettes are filled at the tip with a solution containing one concentration of ligand and then backfilled with another. The concentration of ligand at the membrane is described as a function of time by the equation for diffusion in a cone, allowing response vs. time data to be transformed into a dose-response curve. For Xenopus myocyte cholinergic receptors, examples of the use of this method are given for several concentration-dependent reactions including blockade by the local anesthetic QX-222, activation by acetylcholine, and modulation of current amplitude by sodium ions. Several methods of analyzing the nonstationary channel kinetics are presented, including a pseudo-stationary approach that uses interval likelihood maximization.

Acetylcholine↗
PubMed1990

Human umbilical cord blood: a clinically useful source of transplantable hematopoietic stem/progenitor cells.

This is a review and discussion of studies leading to the first use of human umbilical cord blood, material usually discarded, for the provision of stem/progenitor cells for clinical hematopoietic reconstitution. This prospect arose as a result of extensive studies of the harvesting and cryopreservation of cord blood and of its numerical content of progenitor cells demonstrable in vitro. A male patient with Fanconi anemia (FA) was conditioned with a modified regimen of cyclophosphamide and irradiation that accommodates the abnormally high sensitivity to these agents that is characteristic of FA. Cryopreserved cord blood had been retrieved at birth from a female sibling known from prenatal testing to be unaffected by FA and to be human leukocyte antigen (HLA)-compatible with the prospective sibling recipient. After conditioning and therapeutic infusion of thawed cord blood, successful hematopoietic reconstitution was indicated by the general health of the patient, who had previously required supportive transfusions, by satisfactory hematological criteria and by counts of hematopoietic progenitor cells of various types in the bone marrow. Complete engraftment of the myeloid system with donor cells was evident from cytogenetics, ABO typing, study of DNA polymorphisms, and normal cellular resistance to cytotoxic agents that reveal the fragility of FA cells; the blood contained a residuum of host lymphocytes exhibiting chromosomal damage, but the trend has been towards eliminating these damaged cells. This implies that cord blood from a single individual should provide sufficient reconstituting cells for effective hematopoietic repopulation of an autologous or an HLA-compatible allogeneic recipient.

Blood Transfusion↗
PubMed1990

Transplantation of umbilical cord blood in Fanconi's anemia.

It has been shown that human umbilical cord blood contains stem/progenitor cells comparable in number to that of adult bone marrow. We report here the first successful cases of transplantation of umbilical cord blood cells. The patients were suffering from Fanconi's anemia, complicated by severe aplastic anemia. During pregnancy, it was shown that the mother was carrying a sibling unaffected by the disease and with HLA identical to the patient. Cord blood was collected and frozen in liquid nitrogen at birth. After conditioning with low-dose cyclophosphamide (20 mg/kg) and thoraco-abdominal irradiation (5 grays), the patients received a cord blood transplant of thawed cells. Three patients have been transplanted without any immediate side-effect. One has not enough follow-up, but two patients are alive and well with complete donor hematologic reconstitution and no chronic graft versus host disease. Potential developments of this technique are an extension of applicability with regard to other diseases that might be transplanted and whether such transplants can be performed in adults. The relative immaturity of the lymphoid system at birth may be advantageous in decreasing the graft versus host reaction if these cells are used in a mismatched transplantation. Cord blood cell banks may be useful for transplants in patients lacking an HLA-identical donor.

Child↗
PubMed1987

Activation of the primary kinetic modes of large- and small-conductance cholinergic ion channels in Xenopus myocytes.

1. The kinetic properties of single acetylcholine (ACh)-activated ion channels in tissue-cultured Xenopus myocytes have been examined in cell-attached patches. The rates of agonist binding and channel gating were inferred from the durations of open and closed intervals from channels exposed to 40 nM-200 microM-ACh. The predominant kinetic forms of large- (gamma 60) and small-conductance (gamma 40) cholinergic channels were compared. 2. At high [ACh], bursts were defined so that they primarily reflect sojourns in activatable states. The probability that a channel is open within a burst (Po) increases between 2 and 200 microM-ACh. Po is half-maximal at approximately 5 microM for gamma 40 channels and at approximately 25 microM for gamma 60 channels. 3. Open interval durations for gamma 40 channels are distributed as the sum of two exponentials, with the slow component (tau approximately 2.8 ms) accounting for greater than 80% of the total. Open interval durations for gamma 60 channels are often distributed as a single exponential with an apparent time constant of approximately 0.8 ms. For both conductance forms of channel, open interval durations show no significant dependence on [ACh] in the range 0.04-10 microM, but decrease at higher [ACh] in a manner consistent with channel block by agonist molecules. 4. Closed interval durations within bursts (2-100 microM-ACh) for gamma 60 or gamma 40 channels are described by the sum of two or three exponentials. For both conductance forms of channel the apparent time constant of the fastest component is approximately 40 microseconds and does not change significantly with [ACh], and the time constant of the predominant, slowest component (tau slow) decreases with increasing [ACh]. 5. For gamma 40 channels, at high [ACh] tau slow saturates at approximately 0.17 ms, while no saturation is apparent for gamma 60 channel tau slow values up to 200 microM-ACh. Below 50 microM-ACh, gamma 40 tau slow values are approximately 1.5 times shorter than gamma 60 values. 6. Estimates of rate constants for agonist binding and channel gating were obtained by fitting closed interval durations in the range 2-100 microM-ACh. Gamma 60 channels have a greater than 5-fold faster opening rate, approximately 10-fold faster closing rate, and approximately 3-fold lower affinity than do gamma 40 channels. There is some indication of positive co-operativity of ACh binding to gamma 40 channels.

Acetylcholine↗
PubMed1986

Heterogeneous kinetic properties of acetylcholine receptor channels in Xenopus myocytes.

We have used the cell-attached patch-clamp technique to examine the kinetic and conductance properties of acetylcholine receptor channel currents in cultured Xenopus myocytes. At high agonist concentrations (5-100 microM) the currents occurred in bursts of openings. The probability that a channel existed in an ion-conducting conformation during a burst (Po) was adopted as an empirical measure of channel kinetic behaviour. All openings within a given burst were to the same mean current amplitude. However, different bursts could have openings with a mean conductance of either 46 pS (gamma 40) or 64 pS (gamma 60). For gamma 40 bursts there were three predominant populations which could be distinguished by their mean Po values (approximately 0.9, approximately 0.3, and less than 0.01 at 20 microM-acetylcholine). Po values increased as the acetylcholine concentration within the micropipette was increased. About 80% of bursts were from the highest Po population. gamma 60 bursts also occurred in three predominant modes. The highest Po population accounted for greater than 80% of all bursts and had a mean Po of approximately 0.6 at 20 microM-acetylcholine. For both gamma 40 and gamma 60 channels, bursts from the highest Po population had open-interval durations which were approximately 4 times longer than those from bursts from the medium Po population. Closed intervals from gamma 40, high Po bursts were approximately 4 times shorter than those from medium Po bursts. Occasional examples of switching between different kinetic modes were observed, suggesting that the Po populations may represent different activity patterns of a homogeneous channel population.

Acetylcholine↗
PubMed1985

Therapist success and its determinants.

This study examined the relatively unexplored contribution of the therapist's performance in determining outcomes of treatment. Nine therapists were studied: three performed supportive-expressive psychotherapy; three, cognitive-behavioral psychotherapy; and three, drug counseling. Profound differences were discovered in the therapists' success with the patients in their case loads. Four potential determinants of these differences were explored: patient factors; therapist factors; patient-therapist relationship factors; and therapy factors. Results showed that patient characteristics within each case load (after random assignments) were similar and disclosed no differences that would have explained the differences in success; therapist's personal qualities were correlated with outcomes but not significantly (mean r = .32); an early-in-treatment measure of the patient-therapist relationship, the Helping Alliance Questionnaire, yielded significant correlations with outcomes (mean r = .65); among the therapy techniques, "purity" provided significant correlations with outcomes (mean r = .44), both across therapists and within each therapist's case load. The three therapist-related factors were moderately associated with each other.

Adolescent↗
PubMed1971

Does curare affect transmitter release?

1. The effect of curare on the amount of transmitter released by a nerve stimulus was studied in frog and rat nerve-muscle preparations using electrophysiological techniques.2. When the frog sartorius nerve-muscle preparation was exposed to low doses of curare, the amplitudes of spontaneous miniature end-plate potentials and end-plate currents (e.p.c.s, measured under ;voltage clamp' conditions) were reduced to the same extent, suggesting that the drug did not alter the number of transmitter quanta released by nerve stimulation.3. With higher doses of curare in frog muscle treated with glycerol to abolish twitching, quantum content was estimated from the coefficient of variation (CV) of e.p.c.s. The measured CV increased slightly in curare; this increase probably resulted from a relatively greater contribution of random noise to the observed fluctuations when the e.p.c. was reduced by curare.4. In the rat diaphragm, muscle fibres were cut to block twitching. This procedure produced, among other changes, a reduction in the muscle fibre space constant, so that junctional signals were distorted by the cable properties of the muscle fibre when, as often occurred, micro-electrodes were more than 100-200 mu from the end-plate focus. This produced errors in estimates of quantum content; when these errors were accounted for, it appeared that curare did not significantly alter quantum content.5. It is concluded that if curare affects transmitter release at all, its effect must be much smaller than its well known post-synaptic blocking action.

Animals↗