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PubMed2004

Chemoreceptor and vagal influences on genioglossal muscle responses to inspiratory resistive load.

The present study was undertaken to determine the mechanisms underlying the involvement of upper airway dilating muscles in compensatory responses to added inspiratory resistive load. Experiments were performed in tracheostomized, anaesthetised rabbits. The effect of inspiratory resistive loading on the electromyographic activity of the genioglossus muscle, the major dilating muscle of the pharynx, was studied in vagotomized and vagally intact rabbits during spontaneous breathing with a hypoxic gas mixture (10% O(2) in N(2)) or oxygen. In the vagally intact animals the peak value and duration of genioglossus muscle inspiratory activity increased in the first loaded breath before any noticeable change in the arterial blood gases. Hyperoxia decreased, whereas hypoxia increased the immediate response of the genioglossus activity to inspiratory loading. Removal of vagal volume-related feedback (by vagotomy) significantly increased the genioglossus muscle activity; the increase being more under hypoxia than under hyperoxia. In contrast to vagally intact animals, there was no first-breath increase in genioglossus activity during loading. The results indicate that the immediate involvement of the genioglossus muscle in response to inspiratory resistive load is mediated by vagal-volume feedback. Baseline oxygen tension before loading modulates the immediate reflex vagal-related response of the genioglossus muscle.

Animals↗
PubMed1985

Proteolytic fragments identified with domains of the aspartate chemoreceptor.

Two proteolytic fragments generated during the preparation of the aspartate receptor from Salmonella typhimurium have been purified. These fragments are the products of a single cleavage by an endogenous protease after amino acid 259 in the sequence of the intact receptor. Proteolytic fragment 1 (PF1) represents amino acids 1-259 (Mr = 29,000); this unit retains the aspartate-binding function of the intact receptor. The second fragment (PF2) includes residues 260-552 (Mr = 31,000) and has the normal sites of reversible methylation for the receptor. Like the purified intact receptor, this fragment can be methylated in vitro, although at a much slower rate. Circular dichroic measurements suggest that both proteolytic fragments contain substantial alpha-helical structure, approximately 95 and 53% for PF1 and PF2, respectively. No beta-structure could be detected in either fragment. Molecular sieve chromatography in the presence of detergent suggests that PF1 occurs as a stable multimer of an order equivalent to that observed for the detergent-solubilized aspartate receptor, i.e. a tetramer (+/- 1). PF2 is found to have a multimeric form which is sensitive to the removal of detergent. It is proposed that these fragments represent structural and functional domains of the aspartate receptor.

Amino Acid Sequence↗
PubMed1986

[Clinico-morphologic description of insufficiency of chemoreceptors of the ventral surface of the medulla oblongata].

Using the method of reversed respiration, a decrease in the sensitivity of the ventilation regulation system to the hypercapnic stimulus was observed in a patient with acoustic neurinoma. Cytological and morphometric study of the tissue sections revealed a decrease in the size and number of neurocytes in the superficial portions of the ventral side of the medulla oblongata. It is concluded that the above structural changes are responsible for inhibition of the metabolic system of respiration regulation.

Adult↗