The phantom burster model for pancreatic beta-cells.

Pancreatic beta-cells exhibit bursting oscillations with a wide range of periods. Whereas periods in isolated cells are generally either a few seconds or a few minutes, in intact islets of Langerhans they are intermediate (10-60 s). We develop a mathematical model for beta-cell electrical activity capable of generating this wide range of bursting oscillations. Unlike previous models, bursting is driven by the interaction of two slow processes, one with a relatively small time constant (1-5 s) and the other with a much larger time constant (1-2 min). Bursting on the intermediate time scale is generated without need for a slow process having an intermediate time constant, hence phantom bursting. The model suggests that isolated cells exhibiting a fast pattern may nonetheless possess slower processes that can be brought out by injecting suitable exogenous currents. Guided by this, we devise an experimental protocol using the dynamic clamp technique that reliably elicits islet-like, medium period oscillations from isolated cells. Finally, we show that strong electrical coupling between a fast burster and a slow burster can produce synchronized medium bursting, suggesting that islets may be composed of cells that are intrinsically either fast or slow, with few or none that are intrinsically medium.

Gastric fluid measurement by blind aspiration in paediatric patients: a gastroscopic evaluation.

PURPOSE: Numerous investigators have estimated gastric fluid volume using blind aspiration through multi-orificed catheters, but none have confirmed the validity of this technique in infants and children. We sought to validate the accuracy of this technique in a fasted paediatric population by using gastroscopy. Data from several studies were then combined to generate a gastric fluid volume frequency distribution for healthy paediatric patients fasted for surgery. METHODS: This is a prospective study of 17 patients aged six months to 11 yr who underwent elective upper endoscopy at a paediatric teaching hospital. Gastric contents were aspirated blindly with a syringe and a 16 or 18F multi-orificed orogastric tube, and the volume of gastric contents removed in the supine and decubitus positions was measured. Residual gastric fluid was aspirated using an endoscope. Data from 611 infants and children enrolled in previously published studies utilizing the same blind aspiration technique were pooled and a gastric fluid volume frequency distribution was created. RESULTS: Blind aspiration removed 97 +/- 8% of the total gastric fluid volume. In 661 children presenting for elective surgery, the gastric fluid volume was 0.40 +/- 0.45 ml.kg-1. Median volume was 0.27 ml.kg-1, with the 95%ile at 1.25 ml.kg-1 and an upper limit of 4.1 ml.kg-1. CONCLUSION: Blind aspiration of gastric contents accurately estimates gastric fluid volume for paediatric patients fasted for surgery. Population estimates for gastric fluid volume in otherwise healthy fasted paediatric patients are shown.

Improvements in a non-proprietary radiometric medium to allow the detection of some Pseudomonas species and Alcaligenes faecalis.

The addition of [5-14C]glutamate and [14C]formate to a non-proprietary medium containing [14C]glucose, Trypticase, yeast extract, thiotone, and salts enabled the radiometric detection of the presence of nonfermenters of glucose. It did not interfere with the rapid detection of the presence of aerobic and anaerobic sporeforemers and nonsporeformers.

Comparative dynamics of salmonella infection after primary and secondary challenge of mice exposed to 10 and 23 C.

Mortality of mice increased significantly as a result of cold exposure when the animals were challenged orally with Salmonella typhimurium, strain RIA. As reported earlier, cold exposure alone did not kill control animals nor did oral challenge at room temperature. No differences were apparent in the number of Salmonella per gram of liver-spleen, colon, or lung between groups of infected mice housed at 23 and 10 C. The number of bacteria increased equally in liver-spleen samples during the period of increasing mortality in the group housed at 10 C and the period of overt illness in those housed at 23 C. The ability to clear the bloodstream of a secondary intravenous challenge did not seem to be impaired by cold exposure. The bacterial load in the spleen and the rate of change in weight of that organ was equal in animals given a secondary challenge at 10 or 23 C. However, the absolute spleen weight was less in the cold-exposed group as was survival when the secondary challenge was administered 3 days after the primary oral challenge. The studies indicate that endotoxin from S. typhimurium may sensitize mice to the lethal effects of cold exposure. The increase in mortality observed in cold-exposed, infected mice is not due to greater bacterial proliferation in these animals. Rather, the combined stress effects of the bacterial agent(s) and cold may link lympholytic effects to impaired detoxification and increased energy demands, which often leads to lethal vascular collapse in cold-exposed, infected mice.

Radiometric detection of some food-borne bacteria.

Studies on detection of bacteria by radiometric techniques have been concerned primarily with aerobic species in clinical specimens. The data presented here are related to detection of aerobic and anaerobic species that are of significance in foods, by measurement of (14)CO(2) evolved from the metabolism of (14)C-glucose. Salmonella typhimurium and Staphylococcus aureus were inoculated into tryptic soy broth containing 0.0139 muCi of (14)C glucose/ml of medium. Detection times ranged from 10 to 3 hr for inocula of 10(0) to 10(4) cells/ml of broth. Heat-shocked spores of Clostridium sporogenes or C. botulinum were incubated in tryptic soy broth supplemented with Thiotone and NaHCO(3). The medium was rendered anaerobic with N(2). Spores were detected when 0.0833 muCi of labeled glucose was available/ml of medium but not when 0.0139 muCi of glucose was present/ml. The spores required 3 to 4 hr longer for detection than did comparable numbers of aerobic vegetative cells. The results demonstrate the importance of availability of sufficient label in the media and the potential of the application of this technique for sterility testing of foods.

Invasiveness of salmonella administered orally to cold-exposed mice.

Susceptibility to enteric infection with Salmonella was studied in mice housed at different temperatures. The oral doses of S. typhimurium SR-11 and RIA, which caused 50% mortality in animals at 10 C, were about 1/30 and 1/100 of the respective values at 23 C, and that of an avirulent strain of S. enteritidis was also lower in the cold-exposed mice. The frequency of mortality due to Salmonella infection was essentially the same in mice exposed to 34 to 23 C. The divergent responses in the cold and heat probably stem from basic differences in the physiological changes mediated by the two extremes. The pattern and extent of change in weight and rectal temperature were the same among infected mice housed at 10 and 23 C and controls at 10 C, but differed from controls at 23 C. The incidence of Salmonella in samples of liver-spleen, lung, colon, blood, or feces was similar among infected mice housed at 10 and 23 C during a 14-day period of observation. The increased frequency of mortality in cold-exposed infected animals is not due to alterations in invasiveness of the bacteria nor to greater impairment of the thermoregulatory capacity of the mice. It may be attributable, in part at least, to a greater effectiveness of Salmonella toxins as metabolic poisons at low temperatures.

Immunogenicity of irradiated Salmonella typhimurium cells and endotoxin.

The effects of high doses of radiation (1, 5, or 20 Mrad) on the toxicity, pyrogenicity, and immunogenicity of Salmonella typhimurium cells and endotoxin were studied. Toxicity decreased progressively after exposure to 1, 5, or 20 Mrad. The lethal effect of 1-Mrad exposed cells was greater than that of heat-, acetone-, or alcohol-killed preparations. An amount of 5 Mrad is about a 50% end point in terms of inactivation of the lethal lipopolysaccharide or cell-associated determinants. The fever response to radiation-killed salmonellae decreased between 1- and 20-Mrad exposure. The immunogenicity of 1-Mrad-treated cells usually exceeded that of nonirradiated preparations in mouse-protection tests. With increasing radiation doses, there was a dramatic decrease in, but not an abolition of, immunogenicity. Preparations exposed to 20 Mrad which were nonlethal afforded significant protection. The results are interpreted as a reflection of a dissociation of the primary and secondary toxic determinants of endotoxin after irradiation. The data indicate the potential value of radiation sterilization as a means of production of Salmonella vaccine.

Detoxification of Salmonella typhimurium lipopolysaccharide by ionizing radiation.

The efficiency of ionizing radiation in detoxifying the lethal determinant(s) of the lipopolysaccharide (LPS) of Salmonella typhimurium, S. enteritidis, and Escherichia coli in aqueous solution and associated with heat-killed S. typhimurium cells in suspension decreased with doses above 1 Mrad. The 50% end point of inactivation was more than 7.0 Mrad for heat-killed salmonellae and 4.8, 4.5, and 1.0 Mrad for the LPS of S. typhimurium, S. enteritidis, and E. coli, respectively. After exposure to 20 Mrad, S. typhimurium LPS retained a small portion of its lethal properties although the ld(50) was much greater than 9.5 mg per 20-g mouse. However, at -184 C, no inactivation of the lethal determinant(s) occurred after exposure to as much as 20 Mrad. This demonstrated the significance of the indirect effect and the mobility and formation of free radicals. At 22 C, the optical density at 400 mmu increased and the pH decreased with increasing radiation dose, but no qualitative changes were observed in the infrared spectrum. No change was observed in the pyrogenicity of S. typhimurium LPS; a slight decrease in antigenicity was revealed when 6 days, but not when 1 day, elapsed between vaccination and challenge in the mouse protection test. The results were interpreted as evidence of the existence of two or more lethal and antigenic determinants. The differential effect of radiation on these properties and on the pyrogenic component(s) probably are indicative of separate functional sites for lethal, antigenic, and pyrogenic activities.