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Biomedical subjects

J T Martin

Publications and source records attributed to J T Martin.

At least 73 records · Page 4Linked to original sources
PubMed1978

Irreversible ischemic cell injury. Prevention by chlorpromazine of the aggregation of the intramembranous particles of rat liver plasma membranes.

Ischemic rat liver tissue has been shown previously to exhibit a markedly accelerated rate of phospholipid degradation, producing a loss of almost one half the total cellular phospholipid with 3 hours of ischemia. Pretreatment of the rats with chlorpromazine completely prevented the disturbed phospholipid metabolism at the same time that it prevented the cell death associated with as much as 3 hours of ischemia. Lipid-depleted microsomal membranes were shown previously to manifest alterations in their structure and function. The present report documents that similar structural alterations are evident in ischemic liver cell plasma membranes. The technique of freeze-fracture electron microscopy was used to examine the morphology of ischemic liver cell plasma membranes. Freeze-fracture replicas of whole tissue fragments exhibited a diffuse aggregation of the intramembranous particles in the P face of the plasma membranes. The incidence of this change correlated with the duration of ischemia. Pretreatment of the rats with chlorpromazine (20 mg/kg) for 30 minutes before inducing ischemia prevented the aggregation of the membrane-associated particles. These findings establish the existence of plasma membrane alterations in ischemic liver cells. The time course of these changes, their prevention by chlorpromazine, and their similarity to the previously described structural alterations in the microsomal membranes suggest that they are related to the loss of liver cell phospholipid. The data in the present report support the hypothesis that an accelerated phospholipid degradation and its resultant membrane dysfunction are the critical alterations that produce irreversible liver cell injury and, ultimately, cell death in ischemia.

Animals↗
PubMed1977

Imidazole myopathy. Production of the myopathy and its dependence on acetylcholine.

An acetylcholine-mediated myopathy has been produced in the soleus muscle of the rat by the daily injection of imidazole, a compound that accelerates the metabolism of adenosine 3':5' cyclic phosphate by activating the enzyme phosphodiesterase. The imidazole-treated muscles were found to have a lowered resting membrane potential. This study suggests that a decrease in resting membrane potential may make skeletal muscle more vulnerable to necrosis by acetylcholine released during normal activity.

Acetylcholine↗
PubMed1975

Alkaline lysis of mammalian cells for sedimentation analysis of nuclear DNA. Conformation of released DNA as monitored by physical, electron microscopic and enzymological techniques.

The degree of single strandedness of the DNA released from rat liver nuclei by various alkaline lysing solutions (including some with sodium dodecyl sulfate) was determined both before and after sedimentation in alkaline sucrose gradients employing electron microscopy, melting profiles, circular dichroism measurements, and digestibility by S1 nuclease. Regardless of the technique employed, the results obtained following alkaline sucrose gradient centrifugation of the DNA are consistent. The DNA was completely single stranded as judged by electron microscopy, circular dichroism spectra, and digestibility by S1 nuclease, an enzyme that specifically hydrolyzes single-stranded DNA. This was not true if the DNA was analyzed following alkaline lysis of the nuclei but before centrifugation. Under conditions which gave a complete transition to the single-stranded state, as judged by melting profiles and circular dichroism spectra, only 10-15% of the DNA was hydrolyzed by S1 nuclease. An increase in the susceptibility of the released DNA to S1 nuclease was observed with increases in the pH of the lysing solution. In order to release DNA which was single stranded as judged by both physical and enzymological techniques, the rat liver nuclei were lysed for 30 min with a 0.3 M NaOH lysing solution containing 0.5% dodecyl sulfate, 0.3 M NaCl and 0.03 M EDTA.

Animals↗
PubMed1975

Arousal and temporal factors imprinting in mallards.

A number of factors affecting the learning processes in laboratory imprinting were examined. Two factors alone explained the degree to which young ducklings learn the characteristics of a given model: the length of exposure to the model, and the endogenous arousal state of the duckling. A third, the effect of muscular exertion is not warranted. The characteristics of some models are more rapidly learned than others, and the significance of this fact for biochemical studies of learning is discussed. In this study ease of learning coincided with innate preference; this suggests the presence of a neural filtering mechanism in the duckling which alters the assimilation of information into the CNS and hence controls both innate preference and learnability.

Animals↗
PubMed1968

Autolytic enzyme system of Streptococcus faecalis. IV. Electron microscopic observations of autolysin and lysozyme action.

Cell walls (LOG walls) were isolated from cultures of Streptococcus faecalis ATCC 9790 in the exponential phase of growth. These walls were either allowed to undergo autolytic dissolution (in the presence or absence of trypsin) or wall autolysis was inactivated with sodium dodecylsulfate (SDS walls). Inactivated walls were treated either with lysozyme or with isolated, partially purified S. faecalis autolysin. During wall lysis, samples were removed, negatively stained with phosphotungstate, and examined in the electron microscope. Both lysozyme and isolated autolysin appeared to act over the entire surface of SDS walls. After partial dissolution, a fibrous network over the surface was revealed. Lysozyme digestion revealed the presence of prominent, highly-contrasted equatorial and subequatorial bands around the walls. After trichloroacetic acid extraction, the bands were seen less frequently and less distinctly in the partially lysozyme digested walls, suggesting that the bands contained nonpeptidoglycan polymers. In the absence of trypsin (which activates a latent form of the autolysin), autolysis of LOG walls appeared to start at the equatorial bands and to proceed back towards the apex of the coccus. Ribbons of wall material coming off the wide edge of the nearly hemispherical wall fragments were observed. Activation of latent autolysis resulted in lytic action over the entire wall surface. The results are consistent with the previously postulated location of active autolysin at the areas of new wall synthesis and the random location of latent autolysin in LOG walls.

Autolysis↗