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Inhibition and Facilitation in Cardiac Muscle. Introduction: The effects of subthreshold electrical pulses on the response to subsequent stimulation have been described previously in experimental animal studies as well as in the human heart. In addition, previous studies in cardiac Purkinje fibers have shown that diastolic excitability may decrease after activity (active inhibition) and, to a lesser extent, following subthreshold responses (electrotonic inhibition). However, such dynamic changes in excitability have not been explored in isolated ventricular muscle, and it is uncertain whether similar phenomena may play any role in the activation pal-terns associated with propagation abnormalities in the myocardium. Methods and Results: Experiments were performed in isolated sheep Purkinje fibers and papillary muscles, and in enzymatically dissociated guinea pig ventricular myocytes. In all types of preparations introduction of a conditioning subthreshold pulse between two subthreshold pulses was followed by a transient decay in excitability (electrotonic inhibition). The degree of inhibition was directly related to the amplitude and duration of the conditioning pulse and inversely related to the postconditioning interval. Yet, inhibition could be demonstrated long after (> 1 sec) the end of the conditioning pulse. Electrotonic inhibition was found at all diastolic intervals and did not depend on the presence of a previous action potential. In Purkinje fibers, conditioning action potentials led to active inhibition of subsequent responses. In contrast, in muscle cells, such action potentials had a facilitating effect (active facilitation). Electrotonic inhibition and active facilitation were observed in both sheep ventricular muscle and guinea pig ventricular myocytes. Accordingly, during repetitive stimulation with pulses of barely threshold intensity, we observed: (1) bistability (i.e., with the same stimulating parameters, stimulus: response patterns were either 1:1 or 1:0, depending on previous history), and (2) abrupt transitions between 1:1 and 1:0 (absence of intermediate wenckebach-like patterns). Simulations utilizing an ionic model of cardiac myocytes support the hypothesis that electrotonic inhibition in well-polarized ventricular muscle is the result of partial activation of Ik following subthreshold pulses. On the other hand, active facilitation may be the result of an activity-induced decrease in the conductance of IK1. Conclusion: Diastolic excitability of well-polarized ventricular myocardium may be transiently depressed following local responses and transiently enhanced following action potentials. On the other hand, diastolic excitability decreases during quiescence. Active facilitation and electrotonic inhibition may have an important role in determining the dynamics of excitation of the myocardium in the presence of propagation abnormalities.  相似文献   
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Abstract. An eleven-month-old boy is presented with chronic atopic dermatitis and recurrent infections of the skin and respiratory tract, including subcutaneous abscesses. Immunological studies disclosed a neutrophil chemotactic defect, blood eosinophilia and serum hyper IgE. The clinical and analytical data are similar to those of patients previously described by Hill & Quie. A diet free of the allergens which were responsible for the atopic dermatitis reversed the chemotactic defect, the blood eosinophilia and the clinical symptoms.  相似文献   
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ABSTRACT. The chemotactic activity and random motility of neutrophils, was studied in 38 patients with hypovitaminosis D rickets, and compared with 29 healthy controls of matched age. The chemotactic activity derived from the activated rickets serum as well as the amounts of the complement components C4, C3 and C5 was normal, but the cell motility was clearly defective (p<0.001). A possible relationship between defective neutrophil movement and the recurrent infections seen in these patients is suggested. The possible mechanisms responsible for the defect could be the alteration in Ca/P metabolism or a defective action of the vitamin D on the neutrophils.  相似文献   
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Abstract. Lorente, F., Fontán, G., García Rodriguez, M. C., Alba, J. and Ojeda, J. A. (Service of Immunoallergy, Department of Paediatrics and Department of Pathology, La Paz Hospital, Madrid, Spain). Neutrophil chemotactic defect and hypogammaglobulinemia. Acta Paediatr Scand, 69:699, 1980.—A 15-months-old boy developed agranulocytosis after administration of Chloramphenicol and Amynopirine. In spite of total hematological recovery, the patient's immunological study disclosed a persistent neutrophil chemotactic defect and hypogammaglobulinemia. Other studies of specific and non-specific immunity were normal. Neutrophil adherence, random and random stimulated mobility were always within the normal range. The presence of chemotactic inhibitors was discarded. In vitro incubation of his neutrophils with Cytochalasin B at 0.1 µg/ml final concentration, reversed the chemotactic abnormality suggesting a possible cell membrane defect.  相似文献   
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