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Biomedical subjects

L Thomas

Publications and source records attributed to L Thomas.

At least 361 records · Page 20Linked to original sources
PubMed1989

Impaired activity rate responsiveness of an atrial activity-triggered pacemaker: the role of differential atrial sensing in its prevention.

The physiological benefit of rate responsive, single-chamber cardiac pacing is well documented. We studied the activity response of nine atrially placed Activitrax II pacemakers. Seven patients were noted to have an inadequate activity-rate response with maximal pacing rates of 85 to 101 beats/min. Marker Channel analysis revealed that the upper rate timeout was reset by far-field R wave sensing, even when sensing occurred in the atrial refractory period. These 9 pacemakers were tested by atrial sensitivity adjustment for ability to exclude far-field R wave sensing, while preserving P wave sensing. Unipolar implantation data were then examined for predictors of this differential far-R and P-wave sensing. Differential atrial sensing occurred in 4/9 pacemakers (2/2 bipolar in the right atrial appendage; 0/1 bipolar in the coronary sinus; and 4/9 unipolar). An empirically developed index utilizing unipolar implant parameters discriminated outcomes for 8/9 unipolar pacemakers. We conclude that: (1) the rate responsiveness of the atrial Activitrax II pacemaker is limited by far-field R wave sensing even when this occurs during atrial channel refractoriness; (2) reprogramming atrial sensitivity to differentially sensed P and far-field R waves may restore appropriate rate responsiveness; and (3) although a unipolar implant discriminant index may correctly identify adequacy of future rate responsiveness, the atrial application of the Activitrax II pacemaker is cautioned until further validation is forthcoming, particularly when used in unipolar and coronary sinus applications.

Adult↗
PubMed1989

Re-expression of disease-characteristic features of non-bullous congenital ichthyosiform erythroderma (CIE) after grafting of the pathological keratinocyte cultures to athymic mice.

Epidermal keratinocytes separated from skin lesions of non-bullous congenital ichthyosiform erythroderma were investigated in an attempt at experimental reproduction of this keratinization disorder. In vitro studies on growth and differentiation of pathological keratinocytes isolated from the influence of the host's dermal and humoral components were performed using the immersed epidermal cell culture technique. Ten to 25-day-old confluent and stratified cultures were examined by means of photonic and electron microscopy, and stained with various differentiation markers for indirect immunofluorescence studies. The cultured epidermis showed low-grade differentiation and no clear-cut evenly distributed signs of the original disease. Grafting on congenitally athymic nude mice allowed further differentiation of the epidermal sheets and re-expression of the histologic and ultrastructural features of non-bullous congenital ichthyosiform erythroderma. Thus, the purely epidermal origin of this particular form of autosomal recessive ichthyosis could be confirmed. Large amounts of pathological keratinocytes generated from small skin biopsies may be used for experimental purposes after grafting on several athymic animals.

Animals↗
PubMed1988

Identification of synaptophysin as a hexameric channel protein of the synaptic vesicle membrane.

The quaternary structure and functional properties of synaptophysin, a major integral membrane protein of small presynaptic vesicles, were investigated. Cross-linking and sedimentation studies indicate that synaptophysin is a hexameric homo-oligomer, which in electron micrographs exhibits structural features common to channel-forming proteins. On reconstitution into planar lipid bilayers, purified synaptophysin displays voltage-sensitive channel activity with an average conductance of about 150 picosiemens. Because specific channels and fusion pores have been implicated in vesicular uptake and release of secretory compounds, synaptophysin may have a role in these processes.

Animals↗
PubMed1988

Yeast KEX2 endopeptidase correctly cleaves a neuroendocrine prohormone in mammalian cells.

Mammalian cell lines (BSC-40, NG108-15, and GH4C1) that cannot process the murine neuroendocrine peptide precursor prepro-opiomelanocortin (mPOMC) when its synthesis is directed by a vaccinia virus vector were coinfected with a second recombinant vaccinia virus carrying the yeast KEX2 gene, which encodes an endopeptidase that cleaves at pairs of basic amino acid residues. mPOMC was cleaved intracellularly to a set of product peptides normally found in vivo, including mature gamma-lipotropin and beta-endorphin1-31. In GH4C1 cells (a rat pituitary line), product peptides were incorporated into stored secretory granules. These results suggest that the inability of any particular cell line to process a prohormone precursor is due to the absence of a suitable endogenous processing enzyme.

Cell Line↗
PubMed1988

Familial imprinting determines H-2 selective mating preferences.

Inbred male mice typically prefer to mate with females of a different, non-self H-2 haplotype. To determine whether this natural preference is irrevocable or results from familial imprinting, a test system was used which relied on previous observations that B6 males (H-2b) mate preferentially with congenic B6-H-2k rather than B6 females, and B6-H-2k males with B6 females. This preference was reversed in B6 males fostered by B6-H-2k parents and in B6-H-2k males fostered by B6 parents, preference in these cases favoring the same H-2 type. Thus, H-2 selective mating preference is acquired by imprinting on familial H-2 types.

Animals↗