Biomedical subjects

L Zorn

Publications and source records attributed to L Zorn.

4 recordsLinked to original sources

PubMed2000

The mode selection trial (MOST) in sinus node dysfunction: design, rationale, and baseline characteristics of the first 1000 patients.

BACKGROUND: More than 200,000 permanent pacemakers will be implanted in the United States in 2000 at a cost of more than $2 billion. Sick sinus syndrome (SSS) will likely account for approximately half of all cases necessitating implantation. Pacemaker technology permits the selection of ventricular (single-chamber) or dual-chamber devices. However, clinical and outcomes data are inadequate to support a clear recommendation that one or the other type of device be used. METHODS: The Mode Selection Trial (MOST) is a single-blind study supported by the National Heart, Lung, and Blood Institute designed to enroll 2000 patients with SSS. All patients will receive a DDDR pacemaker programmed to VVIR or DDDR before implantation. The average time of follow-up will be 3 years. MOST has a >90% power to detect a 25% reduction in the primary end point-nonfatal stroke or total (all cause) mortality-in the DDDR-treated group. Secondary end points will include health-related quality of life and cost effectiveness, atrial fibrillation, and development of pacemaker syndrome. Prespecified subgroups for analysis will include women and the elderly. Enrollment was completed in October 1999, with a total of 2010 patients. RESULTS: The median age of the first 1000 enrolled patients is 74 years, with 25% of patients 80 years or older. Women comprise 49%, and 17% are nonwhite, predominantly black (13%). Before pacemaker implantation, 22% of patients reported a history of congestive heart failure, 11% coronary angioplasty, and 25% coronary bypass surgery. Supraventricular tachycardia including atrial fibrillation was present in 53% of patients. A prior stroke was reported by 12%. Antiarrhythmic therapy was in use in 18% of patients. CONCLUSIONS: MOST will fill the clinical need for carefully designed prospective studies to define the benefits of dual-chamber versus single-chamber ventricular pacing in patients with SSS. The MOST population is typical of the overall pacemaker population in the United States. Thus the final results of MOST should be clinically generalizable.

Aged↗

PubMed1993

Halothane acts on many potassium channels, including a minimal potassium channel.

There has been considerable controversy over whether general anesthetics act directly on membrane proteins, and if so, whether there are uniquely sensitive protein targets upon which they act. Here, we examine the actions of halothane on a diverse collection of voltage-gated potassium channels expressed in Xenopus oocytes, and find that they are all sensitive at clinically relevant concentrations. To investigate further the molecular basis of this commonality, human and rat minimal potassium (minK) channels, which have exceedingly short amino acid sequences, were examined. Current through these channels is reversibly reduced to 68% of control values by 0.5% (0.34 mM) halothane. A double deletion mutant of the 130-amino acid minK protein, in which 30 amino acids of the N-terminus, thought to be extracellular, and 37 amino acids of the putative intracellular C-terminus are deleted (resulting in a protein in which more than half of both the extracellular and intracellular domains have been removed) responds to low halothane concentrations similarly to the parent channel. While alternative explanations are possible, this result is consistent with a model whereby halothane interacts with the channel protein from within the lipid bilayer.

Animals↗

PubMed1992

Assembly of the oligomeric membrane pore formed by Staphylococcal alpha-hemolysin examined by truncation mutagenesis.

The alpha-hemolysin (alpha HL) from Staphylococcus aureus causes the lysis of susceptible cells such as rabbit erythrocytes (rRBCs). Lysis is associated with the formation of a hexameric pore in the plasma membrane. Here we show that truncation mutants of alpha HL missing 2 to 22 N-terminal amino acids form oligomers on the surfaces of rRBCs but fail to lyse the cells. By contrast, mutants missing 3 or 5 amino acids at the C terminus are very inefficient at oligomerization but do lyse rRBCs, albeit extremely slowly. The C-terminal truncation mutants, retarded as monomers on the cell surface, undergo a conformational change in which the protease-sensitive loop located near the midpoint of the polypeptide chain becomes occluded. Judged by this criterion, polypeptides truncated at the N terminus, frozen as nonlytic oligomers, are in a similar conformation. A second proteolytic site near the N terminus of the polypeptide becomes inaccessible in the lytic pore formed by the wild-type polypeptide, supporting the idea that a second conformational change occurs upon pore formation. These findings suggest a pathway for assembly of the lytic pore in which alpha HL first binds to target cells as a monomer, which is converted to a nonlytic oligomeric intermediate before formation of the pore. In keeping with this model, an N-terminal truncation mutant blocks the slow lysis induced by a C-terminal truncation mutant, presumably by diverting the weakly lytic subunits into inactive oligomers.

Amino Acid Sequence↗

PubMed1992

Functional expression of the alpha-hemolysin of Staphylococcus aureus in intact Escherichia coli and in cell lysates. Deletion of five C-terminal amino acids selectively impairs hemolytic activity.

The alpha-hemolysin gene from Staphylococcus aureus, excluding the 5' region encoding the hydrophobic leader sequence, was amplified from genomic DNA. The identity of the disputed C terminus has been confirmed and revisions made to the internal sequence. The hemolysin is expressed at high levels in Escherichia coli and has been purified to homogeneity from this source. In addition, active [35S-Met]alpha-hemolysin of high specific radioactivity can be generated in an E. coli transcription-translation system. By criteria based on protein chemistry, and biological and electrophysiological assays, the recombinant polypeptide is closely similar to the staphylococcal polypeptide ruling out the possibility of functionally important posttranslational modifications in S. aureus. Convenient new assays utilizing the 35S-labeled polypeptide to measure erythrocyte binding, oligomer formation in detergent and on target cells, and hemolysis have been developed. They have been used to demonstrate that a deletion mutant of alpha-hemolysin, in which five C-terminal amino acids are absent, is severely compromised in its ability both to oligomerize and to lyse rabbit erythrocytes. The mutant polypeptide nevertheless binds tightly to erythrocytes as a monomer, strengthening the idea that oligomerization is required for cell lysis.

Animals↗