Characteristics of lung mechanoreceptors in spotted gar, Lepisosteus oculatus.

Single unit and whole nerve activity were recorded in situ from pulmonary mechanoreceptors in Lepisosteus oculatus in response to step inflation and ramp or flow through ventilation of the lung with air and varying levels of CO2 in air. Slowly adapting receptors (SAR), rapidly adapting receptors (RAR), and CO2-sensitive SAR were identified. Whole nerve activity was often present when transpulmonary pressure was 0 cmH2O and increased due to recruitment and elevated discharge of already-active fibers as lung volume rose. SAR became tonically active once the lung exceeded their threshold volume and demonstrated a rate-sensitive burst of activity on inflation and a rate-sensitive inhibition of activity after deflation of the lung. RAR responded to lung inflation or deflation with a burst of activity. Six of eleven SAR were inhibited by ventilation of the lung with from 6 to 10% CO2 in air, even when lung pressure and volume were kept constant. These receptor discharge characteristics, which were similar to those found for lungfish and amphibians, may account for the reflex responses of gar to lung volume changes.

Chemoreflexive responses to hypoxia and NaCN in longnose gar: evidence for two chemoreceptor loci.

Interactions between internal and external O2 stimulus levels were assessed by measuring the ventilatory and cardiovascular responses to varying water (PWO2) and air bladder (PabO2) O2 levels and intravascular NaCN in anesthetized spontaneously ventilating Lepisosteus osseus. As PWO2 fell, air-breathing frequency (fab) increased. Buccal pressure amplitude (Pb) also increased as PWO2 fell from hyperoxia to normoxia, but hypoxic water depressed Pb. The PO2 in the ventral aorta (VA) fell as PabO2 fell, which stimulated fab and Pb when the gar was in normoxic or hyperoxic water. Thus gill ventilation and air breathing were normally controlled by both internal and external O2 levels, but aquatic hypoxia uniformly depressed gill ventilation regardless of changes in PabO2 levels. Heart rate and blood pressure were unaffected by these changes. NaCN stimulated hypoxic reflexes and bradycardia more quickly when given into the VA or conus than when given into the dorsal aorta. The animals appear to possess internal chemoreceptors that set the level of hypoxic drive and external chemoreceptors that inhibit gill ventilation and shift the ventilatory emphasis from water to air breathing.

Chinese hamster ovarian cell glycoproteins that mediate type 1 piliated gram-negative bacterial adherence.

We used Chinese hamster ovary (CHO) cell lines to define the structures of glycoproteins responsible for Type 1 piliated bacterial adherence. CSH 50 Escherichia coli, a Type 1 piliated bacteria, adhered significantly better than an isogenic nonpiliated E. coli to all CHO lines tested. CSH 50 E. coli adhered least well to CHO cells expressing intact complex type oligosaccharides on cell surface glycoproteins. CSH 50 adherence increased when shorter oligosaccharides were present and was maximal when mannose groups were present in terminal, nonreducing positions. Five high mannose type glycoproteins, with molecular weights of 79, 75, 55, 50, and 37 kD, were identified as high affinity ligands for Type 1 piliated bacteria. Our results suggest that alterations in cell surface carbohydrates may increase adherence of Type 1 piliated gram-negative bacteria to cells.

Characteristics of aerobic gram-negative bacteria colonizing critically ill patients.

Adherence of gram-negative bacteria (GNB) to epithelial surfaces is important for GNB colonization to occur. Pili, rodlike structures projecting from the outer membrane of GNB, and GNB surface hydrophobicity have been shown to enhance GNB adherence. We investigated the types of pili and the hydrophobicity of aerobic GNB colonizing the stomach, oropharynx, and trachea of critically ill patients. Piliation and hydrophobicity of oral, tracheal, and gastric GNB were compared with that of commensal GNB isolated from patients' rectums. Significantly more oropharyngeal than rectal GNB were piliated, and the most common type of pili present was type 1, or mannose-sensitive pili. Mannose-resistant and P pili were present less often, and no colonizing GNB had S pili. Colonizing GNB were hydrophilic rather than hydrophobic, and no differences in hydrophobicity were noted between colonizing GNB and rectal isolates. Our results suggest that pili may be important for oropharyngeal GNB colonization.

Respiratory epithelial carbohydrate levels of rats with gram-negative bacillary colonization.

One mechanism by which severe illness or stress might facilitate adherence and colonization of GNB to respiratory epithelium is by altering epithelial cell surface carbohydrates. To investigate this possibility we used radiolabeled lectins to quantitate carbohydrate levels on intact buccal and tracheal epithelium. A rat model of GNB colonization, in which renal infarction was performed to produce colonization, was used. Buccal and tracheal epithelial surface carbohydrate levels from normal rats and rats 48 hours after renal infarction were compared. Buccal and tracheal epithelium from the renal infarction animals had decreased amounts of sialic acid and fucose, and decreased levels of these sugars occurred at the same time that heavy oropharyngeal GNB colonization developed. Tracheas obtained from the infarcted animals bound three times more Type 1 piliated GNB than normal tracheas. Sialic acid and fucose levels are decreased early after stress, and we speculate that altered epithelial carbohydrates may predispose to GNB colonization by exposing binding sites for GNB.