A quantitative study of the calcium-magnesium antagonism in isolated strips of guinea-pig ileum.

The effect of increasing magnesium concentration (0.61, 1.22, 2.44 and 4.88 mM) on the acetylcholine dose-response curve of isolated strips of the longitudinal muscle of the guinea pig ileum was studied qualitatively and quantitatively in Krebs solution with 2.55 and 5.10 mM calcium. The quantitative study was based on a hypothesis assuming the competition of both ions for a common binding site in the cell "stores" from which the calcium is mobilized following cholinergic receptor activation. The theoretical equations fit the experimental data and allow the calculation of the calcium and magnesium equilibrium constants. As a cross-check two groups of experiments were done to compare the influence on the acetylcholine dose-response curve of a gradual decrease of extracellular calcium either without or with magnesium. The amounts of magnesium used were those theoretically suitable for maintaining a constant amount of calcium in the hypothetical cell "stores". The results agreed with the predictions form the model proposed thus confirming both the hypothesis and the values obtained for the calcium and magnesium equilibrium constants.

A case of keratoconjunctivitis due to Ewingella americana and a review of unusual organisms causing external eye infections.

We report the isolation of Ewingella americana from the conjunctivae of a 38 year old female physician with keratoconjunctivitis associated with the use of soft contact lens. The patient was treated successfully with topical ciprofloxacin. The source of the infection remains unknown. All contact lens cleaning materials used by the patient were sterile. Since the patient was a physician, and this organism has been recorded as a cause of nosocomial infections, we checked whether cases of Ewingella americana had been reported, but none were identified. We have identified 39 bacterial species, 27 fungi, 4 viruses, 7 protozoa, 4 helminths, and 2 arthropods which rarely have been associated with keratitis or conjunctivitis. Infectious diseases specialists and ophthalmologists must be aware of the many different causes of this illness, including Ewingella americana. This organism is a rare bacterial cause of keratoconjunctivitis not previously reported in Brazil. It should be added to the list of unusual cases of external eye infections.

Suppression of mouse IgE response by immune complexes.

The effect of antibodies alone or complexed to antigen on an IgE response was compared in mice immunized with a low dose of antigen. The results demonstrated that immune complexes (ICs) at equivalence were more efficient than antibodies in promoting a suppression of this response when they were injected simultaneously or before, but not after, the antigen. This effect was dose dependent, antigen specific, and long lasting. Furthermore, only isologous ICs were suppressive. ICs prepared with IgG1 antibodies were more effective than ICs prepared with IgG2. Digestion of the Fc fragment of the antibody eliminated completely the suppressive action of antibodies alone, but not of ICs. These results indicate that, whereas an Fc-dependent mechanism is responsible for the effect of antibodies, an additional mechanism is also operating in suppression induced by ICs.