Showing papers by "Mark D. Johnson published in 1988"

Characterization of dystrophin in muscle-biopsy specimens from patients with Duchenne's or Becker's muscular dystrophy

Abstract: A deficiency of the protein dystrophin has recently been shown to be the probable cause of Duchenne's muscular dystrophy. We sought to determine the relation between the clinical phenotype and the status of dystrophin in muscle-biopsy specimens from 103 patients with various neuromuscular disorders. We found very low levels (less than 3 percent of normal levels) or no dystrophin in the severe Duchenne phenotype (35 of 38 patients), low concentrations of dystrophin in the intermediate (outlier) phenotype (4 of 7), and dystrophin of abnormal molecular weight in the mild Becker phenotype (12 of 18). Normal levels of dystrophin of normal molecular weight were found in nearly all the patients (38 of 40) with 20 other neuromuscular disorders we studied. These data show the clinical consequences of both quantitative alterations (in Duchenne's and intermediate dystrophy) in a single protein. The biochemical assay for dystrophin should prove helpful in delineating myopathies that overlap clinically with Duchenne's and Becker's dystrophies, and it shows promise as an accurate diagnostic tool.

Construction and characterization of a retroviral vector demonstrating efficient expression of cloned cDNA sequences.

Abstract: We describe the construction and properties of a retroviral expression vector, designated pMV-7, designed to transfer unselected cDNAs and produce their encoded proteins in recipient cells. The vector is flanked by the long terminal repeats (LTRs) of the Moloney murine sarcoma virus (MSV) and contains the selectable drug resistance gene neo under the regulation of the herpes simplex virus (HSV) thymidine kinase (tk) promoter. Unique Eco RI and Hind III sites facilitate the introduction of sequences whose transcription is regulated by the 5' LTR. We have inserted cDNAs encoding: (i) the human lymphocyte antigen T4, (ii) the human lymphocyte antigen T8, and (iii) the murine hypoxanthine-guanine phosphoribosyl transferase (HPRT), into the pMV-7 vector. These constructions were used to transduce recipient cells to the neo+ phenotype. In each case, functional assays demonstrated that 65-92% of the neo+ clones produced the appropriate protein encoded by its corresponding cDNA. These clones were characterized further by analyzing the expression of vector-regulated transcripts. The neo+T4+ clones expressed a single full-length LTR-to-LTR transcript as detected by a T4 probe. The neo+T8+ clones, however, expressed both a full-length LTR-to-LTR transcript and an additional smaller transcript as detected by a T8 probe. This smaller transcript probably resulted from the utilization of cryptic signals which control 3' RNA processing. Furthermore, all of the neo+ clones expressed a transcript that initiated from the tk promoter, contained the neo gene, and used polyadenylation signals provided by the 3' LTR. Thus, the pMV-7 vector is capable of high-efficiency transfer and high-frequency expression of the cDNA-encoded protein.

Electron spin injection and detection at a ferromagnetic‐paramagnetic interface (invited)

Abstract: A new technique for investigating conduction electronmagnetization is presented. A coupling between electronic charge and spin transport in ferromagnetic metals follows from generalizing the linear transportequations. In practice, this means that ferromagneticfilms act as conduction electron spin polarizers. At an interface between a ferromagnetic and a paramagnetic metal, one can inject and detect nonequilibrium magnetization in the paramagnet, and use sensitive electric measurements to probe spin transport. Application of a small external magnetic field dephases the spins. The result is a new technique for measuring conduction spin relaxation times, which is demonstrated on bulk aluminum samples. Three advantages of the technique make it applicable to a wide range of studies. (1) The measurement can be made in the limit of zero field so that systems with interesting properties which are altered or destroyed by magnetic fields can now be probed (spin glasses, superconductors, metals with g anisotropies). (2) A SQUID voltmeter with picovolt noise floor provides a sensitivity that allows detection of one nonequilibrium spin in a background of 101 2 equilibrium spins. (3) The experimental geometry utilizes microfabrication techniques and is ideal for application to small‐size systems that are inaccessible to conventional electron spin resonance methods. The geometry conveniently needs but one good surface; other sample surfaces are available for alteration i n s i t u for the study of surface relaxation effects. Finally, there are obvious applications to the study of ferromagnets and interfaces.

Continuous epidural infusion of alfentanil and bupivacaine for labor and delivery

Abstract: The purpose of this study was to compare alfentanil and fentanyl used in combination with bupivacaine in a continuous infusion epidural technique during labor and delivery. Thirty nine ASA I parturients had epidural analgesia induced with 0.25% bupivacaine and were then assigned in a randomized double-blind fashion to receive a continuous infusion of 0.125% bupivacaine containing either 5 micro/ml of alfentanil or 2 micro/ml of fentanyl at a rate of 10 ml/h. Analgesia assessed by visual analog scores was significantly better during both stage I and stage II of labor in the group receiving alfentanil. No significant maternal or neonatal side-effects were demonstrated.

Johnson and Silsbee reply.

Abstract: A reply to the comment on niobium nonequilibrium superconductivity is presented.New crystallographic and magnetic field effects were considered.Now in response to the comment the interpretation of the data have been reviewed and in addition computer simulation have been carried out taking into the effects of inhomogeneity. (AIP)