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Biomedical subjects

R M Johnson

Publications and source records attributed to R M Johnson.

At least 163 records · Page 9Linked to original sources
PubMed1975

The kinetics of resealing of washed erythrocyte ghosts.

The kinetics of resealing, defined as the recovery of impermeability to macromolecules, of well-washed human erythrocyte ghosts has been determined. The resealing process is first-order at temperatures above 20-25 degrees C in isotonic salt, with rate constants ranging from 0.01-0.15 min-1. Below 20 degrees C, resealing occurs, but a long lag period is observed. Other erythrocyte membrane properties suggest a transition at about 20 degrees C, and it is possible that resealing rates are a measure of membrane fluidity. A temperature-induced reduction of resealed ghost volume was also observed. The effect of ionic strength on resealing parameters was determined. Low ionic strength buffers prevent resealing, which is also consistent with resealing as a lipid-related event. The effect of microtubule disrupting drugs and changes in the method of preparing ghosts are also described.

Cell Membrane↗
PubMed1975

Vitamin E deficiency in the rat. Cytoplasmic factors required for suppression of mitochondrial respiratory decline.

Liver cytoplasm from either vitamin E-deficient or normal rats has been shown to suppress mitochondrial respiratory decline induced by microsomes in vitro. The present study is an attempt to identify cytoplasmic factor(s) responsible for this suppression. The effect of cytoplasm from both groups of animals could be removed by trichloroacetate precipitation, boiling, and dialysis against 0.3 M mannitol-o.1 mM Tris buffer, pH 7.4, but not by aging or extraction with isooctane. The addition of oxalacetate of alpha-ketoglutarate plus asparate to cytolplasm potentiated the suppressant effect. Dialyzed cytoplasm was not effective in depressing the respiratory decline. However, the addition of NAD, osalacetate, or alpha-ketoglutarate plus aspartate to dialyzed cytoplasm restored its ability to depress the respiratory decline. When oxalacetate or alpha-ketoglutarate plus aspartate was added to fresh cytoplasm, followed by dialysis, the effect of these compounds was not seen. These results suggest that cytoplasmic factor(s) required for suppression of the respiratory decline were enzymes of the malate shuttle and transamination, which are heat labile and trichloroacetate precipitable, plus the dialyzable metabolites that are associated with these enzymes in the generation of NAD in mitochondria.

Animals↗
PubMed1975

Biomechanical analysis of clinical stability in the cervical spine.

This study was undertaken because there is a dearth of objective information in the literature on the clinical instability of the cervical spine below C2. To our knowledge, it is the first biomechanical investigation designed to analyze clinical stability. We have carried out a quantitative analysis of the behavior of the spine as a function of the systematic destruction of various anatomic elements. Under controlled conditions designed to maintain the biological integrity of the specimens, 17 motion segments from 8 cervical spines were analyzed. The spines were studied with either flexion or extension simulated using physiologic loads. Some of the more important findings are: (1) In sectioning the ligaments, one observes small increments of change followed without warning by sudden, complete disruption of the spine; (2) Removal of the facets alters the motion segment such that in flexion, there is less angular displacement and more horizontal displacement; (3) The anterior ligaments contribute more to stability in extension than the posterior ligaments and in flexion, the converse is true; (4) The adult cervical spine is unstable, or on the brink of instability, when any of the following conditions are present: a) All the anterior or all the posterior elements are destroyed or unable to function. b) More than 3.5 mm horizontal displacement of one vertebra in relation to an adjacent vertebra measured on lateral roentgenograms (resting or flexion-extension). c) More than 11 degrees of rotation difference to that of either adjacent vertebra measured on a resting lateral or flexion-extension roentgenogram. These findings can be aptly applied to clinical situations and when instability as determined by the above criteria is present, surgical fusion or some other method to achieve stability should be seriously considered. Work is continuing on this problem as we do not consider this to be altogether complete or definitive. Hopefully, this initial study will stimulate further scientific and clinical investigations.

Adult↗
PubMed1975

Some new observations on the functional anatomy of the lower cervical spine.

The ligaments are a major stabilizing component of the cervical spine and are critical for spinal stability as well as stabilization therapy. Relatively little information is available on the anatomic details and function of the cervical ligaments. Fifteen fresh cervical spines were dissected and the ligaments examined grossly and functionally. Eight different intrinsic ligaments of the lower cervical spine were identified. The largest and most rigid of these are the annulus fibrosus, posterior longitudinal ligament, and capsular ligament. By virtue of their size and certain biomechanical observations, these ligaments stabilize the cervical spine. The other ligaments play a more specialized and secondary role. The intertransverse ligaments, although thin and frail, are consistently found and appear to limit rotation and lateral bending, the anterior longitudinal ligament limits extension and the interspinous and supraspinous ligaments limit spinal flexion. Under physiologic conditions, the elastic ligamentum flavum permits extension of the spine without impinging upon the spinal cord or nerve roots. As a group, the ligaments of the cervical spine control motion within finite limits without jeopardizing spinal cord or nerve root function.

Adult↗
PubMed1975

Effects of vitamin E deficiency on GSH-induced swelling of rat liver mitochondria.

Liver mitochondria from alphatocopherol deficient rats swell more rapidly, both spontaneously and in the presence of GSH, than those from control animals. The increased swelling of deficient mitochondria induced by GSH was completely eliminated when mitochondria were left longer than two hours at 0 degrees in the suspending medium. GSH-induced swelling of liver mitochondria from alpha-tocopherol deficient rats is reversed by ATP, polyvinyl pyrrolidone (PVP) and by oral administration alpha-tocopherol (2 mg/day per rat). Swelling of mitochondria in the above system was completely inhibited by the respiratory chain inhibitor, cyanide (.001 M), and partially by azide (0.001 M). We suggest that the swelling tendency of liver mitochondria from alpha-tocopherol deficient rats might be associated with an altered respiratory mechanism and/or an alteration in membrane permeability.

Adenosine Triphosphate↗