gramicidin-a and Cystic-Fibrosis

Antimicrobial peptides are naturally occurring antibiotics. As part of the innate immune system of vertebrates they have direct antimicrobial function. Further, they can act as mediators of inflammation. Their antimicrobial spectrum covers gram-positive and -negative bacteria as well as fungi and certain viruses. Based on their structure, antimicrobial peptides can be divided into several families. Peptides of the defensin, cathelicidin, and histatin families have been isolated from humans, where they have been found in defense cells, such as macrophages or neutrophils, as well as in epithelial cells. Decreased production of antimicrobial peptides is associated with immune deficiencies. Further, lung disease in cystic fibrosis may be linked to the dysfunction of antimicrobial peptides. Based on naturally occurring antimicrobial peptides, derivates of these molecules were developed as innovative antibiotic drugs. The present review focuses on the biology of antimicrobial peptides as well as their potential as drugs.

Topics: alpha-Defensins; Anti-Bacterial Agents; Antimicrobial Cationic Peptides; beta-Defensins; Carrier Proteins; Cathelicidins; Clinical Trials as Topic; Common Variable Immunodeficiency; Cystic Fibrosis; Drug Design; Gramicidin; Humans; Immunity, Cellular; Inflammation Mediators; Polymyxins

Cystic fibrosis has been characterized as a defect in the regulation of cyclic AMP-dependent transepithelial chloride transport. The activation of cyclic AMP-dependent protein kinase A by cyclic AMP occurs normally in cystic fibrosis cells, but they fail to transport chloride ions in response to protein kinase A stimulation. Defective chloride secretion and abnormal electrolyte transport occurs in several organs including the lung, sweat glands, intestine and pancreas. The present work was aimed at exploring whether the same or similar regulatory systems are functional in platelets, and if they are altered or deficient in individuals with cystic fibrosis. Chloride transport in platelets from normal subjects and from cystic fibrosis patients was measured by cell sizing techniques where chloride permeability is the limiting factor. In platelets from healthy volunteers, the chloride channel blocker, 5-nitro-2-(3-phenylpropylamino) benzoic acid, inhibits the transport in a dose-dependent manner. The preservation of chloride transport capability is shown to be dependent upon the presence of either Ca2+ or two divalent cation substitutes, Cd2+ or Cu2+. It is also shown that in normal subjects 0.1 mumol/l prostaglandin E1, which elevates cyclic AMP 6 times and abolishes platelet aggregation, significantly enhances the rate constant of the transport. Furthermore, in five out of nine cystic fibrosis patients studied, platelet chloride transport did not respond to stimulation by prostaglandin E1.

Topics: Adolescent; Alprostadil; Blood Platelets; Cations; Child; Child, Preschool; Chloride Channels; Cyclic AMP; Cystic Fibrosis; Cystic Fibrosis Transmembrane Conductance Regulator; Egtazic Acid; Female; Gramicidin; Humans; Male; Metals; Nitrobenzoates

We describe a simple and rapid technique for assaying both constitutive and regulated plasma membrane Cl- conductances. The method uses right-angle light scattering to measure the rate of swelling of cells in suspension, in which the anion conductance is rate limiting for swelling, due to introduction of high plasma membrane cation conductance using gramicidin. The technique was verified using Chinese hamster ovary cells and mouse L cells, both stably transfected with the cystic fibrosis transmembrane conductance regulator (CFTR), to confer a specific cAMP-activated Cl- conductance not normally present in these cell types. In agreement with results obtained using other methods for assaying Cl- permeability in these cells, forskolin stimulated a significant increase in plasma membrane Cl- conductance in CFTR-expressing cells, as indicated by an increase in light scattering. That the enhanced light scattering by the cells was the result of cell swelling due to NaCl influx was shown by ion substitution experiments, in which no forskolin-induced increase in light scatter occurred in N-methyl-D-glucamine Cl- or Na+ gluconate medium. Enhanced light scattering was also observed in both CFTR-expressing and control cells stimulated with the Ca2+ ionophore, ionomycin. Extracellular anion substitution, to exploit the inwardly directed halide gradient utilized in this protocol, enabled determination of the anion selectivities of both the cAMP- and Ca(2+)-activated Cl- channels. Thus this technique provides a simple optical method for rapidly assaying not only constitutive and regulated Cl- conductance pathways but also their anion selectivities.

Topics: Animals; Calcium; Cell Line, Transformed; Cell Membrane; Chlorides; Cyclic AMP; Cystic Fibrosis; Cystic Fibrosis Transmembrane Conductance Regulator; DNA; Electric Conductivity; Gramicidin; Ionomycin; Light; Membrane Proteins; Reference Values; Scattering, Radiation

Normal values of mean cell volume (M.C.V.) and of distribution of single cell volumes (S.C.V.) have been observed in erythrocytes of patients with cystic fibrosis using an electronical particle-volume analyzer (sheath flow detector). From these results a strong defect in red cell salt transport seems improbable. Valinomucin induces shrinking (by increase of K+ permeability) and gramicidin D induces swelling (by increase of Na+ permeability) of normal erythrocytes. Addition of C.F. sweat to normal erythrocytes induces no volume change. From this result no influence of the "C.F. factor" on passive ion permeability is concluded.

Topics: Cystic Fibrosis; Erythrocytes; Gramicidin; Humans; Ion Exchange; Permeability; Potassium; Sodium; Sweat; Valinomycin