ABSTRACT
A sustained effort in biochemical, biophysical and physiological research is devoted to the characterization of the transfer of ions and molecules between biological membranes and their aqueous environment. The transported molecules include compounds with substantial structural and physico-chemical differences. It is widely assumed that the biological activity of these compounds arises as a result of binding to active sites in membrane-bound proteins, while the lipid background is considered to play a more passive role. In the simple, symmetric, four-state carrier model for transport of a single solute, transport is down the concentration gradient of that solute. However, a simple modification of this model results in transport up the solute concentration gradient.
Subject(s)
Biological Transport, Active , Models, BiologicalABSTRACT
BACKGROUND: The predictions of the Hodgkin-Huxley model do not accurately fit all the measurements of voltage-clamp currents, gating charge and single-channel currents. There are many quantitative differences between the predicted and measured characteristics of the sodium and potassium channels. For example, the two-state gate model has exponential onset kinetics, whereas the sodium and potassium conductances show S-shaped activation and the sodium conductance shows an exponential inactivation. In this paper we shall examine a more general channel model that can more faithfully represent the measured properties of ionic channels in the membrane of the excitable cell. METHODS: The model is based on the generalisation of the notion of a channel with a discrete set of states. Each state has state attributes such as the state conductance, state ionic current and state gating charge. These variables can have quite different waveforms in time, in contrast with a two-state gate channel model, in which all have the same waveforms. RESULTS: The kinetics of all variables are equivalent: gating and ionic currents give equivalent information about channel kinetics; both the equilibrium values of the current and the time constants are functions of membrane potential. The results are in almost perfect concordance with the experimental data regarding the characteristics of nerve impulse. CONCLUSIONS: The expected values of the gating charge and the ionic conductance are weighted sums of the state occupancy probabilities, but the weights differ: for the expected value of the gating charge the weights are the state gating charges and for the expected value of the ionic conductance the weights are the state conductances. Since these weights are different, the expected values of the gating charge and the ionic conductance will differ.
Subject(s)
Ion Channels/physiology , Electrophysiology , Models, Theoretical , Time FactorsSubject(s)
Skin Diseases, Bacterial/diagnosis , Streptococcal Infections/diagnosis , Streptococcus agalactiae , Streptococcus pyogenes , Adolescent , Adult , Aged , Aged, 80 and over , Bacterial Vaccines/therapeutic use , Child , Child, Preschool , Combined Modality Therapy , Female , Humans , Immunologic Tests , Infant , Male , Middle Aged , Penicillins/therapeutic use , Serotyping , Skin Diseases, Bacterial/prevention & control , Skin Diseases, Bacterial/therapy , Streptococcal Infections/prevention & control , Streptococcal Infections/therapy , Streptococcus agalactiae/classification , Streptococcus agalactiae/isolation & purification , Streptococcus pyogenes/classification , Streptococcus pyogenes/immunology , Streptococcus pyogenes/isolation & purification , Toxoids/therapeutic useSubject(s)
Population Surveillance , Registries , Streptococcal Infections/epidemiology , Humans , Incidence , Microbial Sensitivity Tests , Penicillin G/pharmacology , Prevalence , Registries/statistics & numerical data , Romania/epidemiology , Serotyping , Streptococcal Infections/microbiology , Streptococcus/classification , Streptococcus/drug effects , Streptococcus/isolation & purificationABSTRACT
297 S. pneumoniae strains isolated from patients with different pneumococcal infections during 1990-1991 were tested for the sensitivity to antibiotics--by the diffusimetric method to 9 antibiotics (Penicillin (6 micrograms), Ampicillin (10 micrograms), Erythromycin (15 micrograms), Oxacyllin (5 micrograms), Streptomycin (50 micrograms), Tetracycline (50 micrograms), Chloramphenicol (50 micrograms), Rifampicin (6 micrograms), and Kanamycin (30 micrograms) and by MIC determination to Penicillin and Erythromycin. 30% of S. pneumoniae strains were resistant to Penicillin and Erythromycin corresponding to a MIC > or = 1 UP/ml or > or = 1 microgram E/ml. The most active antibiotics were Chloramphenicol and Rifampicin and the less active: Tetracycline, Kanamycin and Streptomycin. A relation between the origin and serotype of the strains and the sensitivity to antibiotics was revealed. The strains from the throat, conjunctive and otic secretions and belonging to serotypes 19, 6 and 14 showed the highest levels of resistance to all antibiotics. A good correlation between MIC and diffusion method results was observed to Erythromycin and no correlation to Penicillin. In this last case the results of MIC determination to Penicillin were better correlated with the results of inhibitions diameters to Oxacyllin, method which have to be recommended.
