NATURE OF THE ACTION CURRENT IN NITELLA : IV. PRODUCTION OF QUICK ACTION CURRENTS BY EXPOSURE TO NACl

Treatment of Nitella with NaCl greatly reduces the time required for the action current and produces an action curve with one peak instead of the customary two. The time may be reduced to 0.6 second in place of the usual 15 to 30 seconds. This might be expected if the treatment increased the conductivity of the aqueous part of the protoplasm. The experiments favor this idea although they do not prove its correctness. This effect is prevented by calcium, possibly because calcium inhibits penetration of salts. That penetration is an important factor is indicated by the fact that salts which might be expected to penetrate rapidly have the most effect. Thus NaSCN is more effective than NaCl but Na₂SO₄ has little or no effect. The action of NH₄Cl and LiCl is similar to that of NaCl.

CALCULATIONS OF BIOELECTRIC POTENTIALS : IV. SOME EFFECTS OF CALCIUM ON POTENTIALS IN NITELLA

In Nitella the substitution of KCl for NaCl changes the P.D. in a negative direction. In some cases this change is lessened by adding solid CaCl₂ to the solution of KCl. This may be due to lessening the partition coefficient of KCl or to decreasing the solubility of an organic substance which sensitizes the cell to the action of KCl. Little or no correlation exists between this effect of calcium and its ordinary antagonistic action in producing a balanced solution which preserves the life of the cell indefinitely. CaCl₂ is negative to NaCl but positive to KCl. The effects of mixtures of KCl, NaCl, and CaCl₂ are discussed. The concentration effect of a mixture of KCl + CaCl₂ shows certain peculiarities due to action currents: these resemble those found with pure KCl. These studies and others on Nitella, Valonia, and Halicystis indicate that mobilities and partition coefficients are variable and can be brought under experimental control.

ANESTHESIA PRODUCED BY DISTILLED WATER

Cells of Nitella flexilis Ag. lose their power to respond to ordinary electrical stimulation after 2 or 3 days in distilled water. It returns after a day or so when they are replaced in their normal environment, in a suitable nutrient solution, or in a dilute solution of CaCl(2). Here anesthesia seems to be produced by removing something from the cell and this raises the question whether other cases of anesthesia may be explained in the same way. The antagonistic action of calcium, in some cases at least, appears to depend on its power to prevent substances from leaching out of the cell.

ANESTHESIA IN ACID AND ALKALINE SOLUTIONS

The action of distilled water in producing anesthesia (loss of response to electrical stimulation) in Nitella is hastened by the addition of acid and alkali and retarded by the addition of calcium. The loss of irritability is fully reversible.

DELAYED POTASSIUM EFFECT IN NITELLA

In normal cells of Nitella replacement of NaCl by KCl makes the P.D. much less positive: this is called the potassium effect. Cells which have lost the potassium effect usually show little or no change of P.D. when NaCl is replaced by KCl but an occasional cell responds after a delay. It seems possible that the delay may be largely due to the time required for potassium to combine with an organic substance, thus forming a compound which sensitizes the protoplasmic surface to the action of potassium.

PACEMAKERS IN NITELLA : II. ARRHYTHMIA AND BLOCK

Many forms of irregular rhythm and of partial block occurring in the vertebrate heart can be duplicated in Nitella. In order to observe these phenomena the cells of Nitella are kept for 6 weeks or more in a nutrient solution. They are then exposed for 3 hours or less to 0.01 M NaCl, NaSCN, or guanidine chloride, which reduce the time required for the action current to about 1 second (the normal time is 15 to 30 seconds). A pacemaker is established at one end of the cell by placing it in contact with 0.01 M KCl. This produces action currents at the rate of about 1 a second. Apparently some parts of the cell are unable to follow this rapid pace and hence fall into irregular rhythms (arrhythmia) and fail to register all the impulses (partial block).

REVERSIBLE LOSS OF THE POTASSIUM EFFECT IN DISTILLED WATER

Not only does distilled water take away the irritability of Nitella but it also changes its behavior toward potassium. In normal cells potassium is strongly negative to sodium but after sufficient exposure to distilled water this effect disappears. It can be restored by returning the cells to their normal environment or to a suitable nutrient solution. This change in the protoplasm seems to be chiefly in its outer surface.

Amyloid protofibrils of lysozyme nucleate and grow via oligomer fusion

The mechanisms linking deposits of insoluble amyloid fibrils to the debilitating neuronal cell death characteristic of neurodegenerative diseases remain enigmatic. Recent findings implicate transiently formed intermediates of mature amyloid fibrils as the principal toxic agent. Hence, determining which intermediate aggregates represent on-pathway precursors or off-pathway side branches is critical for understanding amyloid self-assembly, and for devising therapeutic approaches targeting relevant toxic species. We examined amyloid fibril self-assembly in acidic solutions, using the model protein hen egg-white lysozyme. Combining in situ dynamic light scattering with calibrated atomic-force microscopy, we monitored the nucleation and growth kinetics of multiple transient aggregate species, and characterized both their morphologies and physical dimensions. Upon incubation at elevated temperatures, uniformly sized oligomers formed at a constant rate. After a lag period of several hours, protofibrils spontaneously nucleated. The nucleation kinetics of protofibrils and the tight match of their widths and heights with those of oligomers imply that protofibrils both nucleated and grew via oligomer fusion. After reaching several hundred nanometers in length, protofibrils assembled into mature fibrils. Overall, the amyloid fibril assembly of lysozyme followed a strict hierarchical aggregation pathway, with amyloid monomers, oligomers, and protofibrils forming on-pathway intermediates for assembly into successively more complex structures.

Oxygen for treatment of severe pneumonia in The Gambia, West Africa: a situational analysis

SETTING

Health facilities in The Gambia, West Africa.

OBJECTIVES

Oxygen treatment is vital in pneumonia, the leading cause of death in children globally. There are shortages of oxygen in developing countries, but little information is available on the extent of the problem. We assessed national oxygen availability and use in The Gambia, a sub-Saharan African country.

METHODS

A government-led team visited 12 health facilities in The Gambia. A modified World Health Organization assessment tool was used to determine oxygen requirements, current provision and capacity to support effective oxygen use.

RESULTS

Eleven of the 12 facilities managed severe pneumonia. Oxygen was reliable in three facilities. Requirement and supply were often mismatched. Both oxygen concentrators and oxygen cylinders were used. Suboptimal electricity and maintenance made using concentrators difficult, while logistical problems and cost hampered cylinder use. Children were usually triaged by trained nurses who reported lack of training in oxygen use. Oxygen was given typically by nasal prongs; pulse oximetry was available in two facilities.

CONCLUSIONS

National data showed that oxygen availability did not meet needs in most Gambian health facilities. Remedial options must be carefully assessed for real costs, reliability and site-by-site usability. Training is needed to support oxygen use and equipment maintenance.

Could mainstream anti-smoking programs increase inequalities in tobacco use? New Zealand data from 1981-96

OBJECTIVE

To examine changes in the socio-economic and ethnic distribution of smoking in the New Zealand population from 1981 to 1996, and to consider the implication of these data for policies aimed at reducing tobacco consumption.

METHODS

Cross-sectional data were taken from 4.7 million respondents to the 1981 and 1996 New Zealand Censuses and 4,619 participants in a 1989 national survey, aged 15 to 79 years. Smoking prevalence rates were calculated by socio-economic position and ethnicity.

RESULTS

Smoking prevalence fell in the period 1981-96 in every population group. However, socio-economic and ethnic differences in smoking increased in relative terms. Smoking prevalence ratios comparing the least advantaged with the most advantaged groups increased in men from 1.20 to 1.53 by income, 1.54 to 1.85 by education, and 1.49 to 1.67 by ethnicity. In women, prevalence ratios increased from 1.17 to 1.51 by income, 1.55 to 2.02 by education, and 1.85 to 2.20 by ethnicity. The greatest increase in socio-economic differences may have occurred during the 1980s, the period of greatest overall decline in total population smoking.

CONCLUSIONS

Socio-economic and ethnic disparities in New Zealanders' smoking patterns increased during the 1980s and '90s, a period of significant decline in overall smoking prevalence.

IMPLICATIONS

Public health programs aimed at reducing tobacco use should pay particular attention to disadvantaged, Indigenous and ethnic minority groups in order to avoid widening relative inequalities in smoking and smoking-related health outcomes.

Organisation of the external region of the starch granule as determined by infrared spectroscopy

Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) was used to study the external regions of starch granules. Native starches (wheat, potato, maize, waxy maize and amylomaize) were analysed and compared to gelatinised and acid-hydrolysed starches. The IR spectra of potato and amylomaize starches were closer to that of highly ordered acid-hydrolysed starch than the other starches. FTIR was not able to differentiate between A- and B-type crystallinity so the difference observed between starches was not related to this factor. The variation between starch varieties was interpreted in terms of the level of ordered structure present on the edge of starch granules with potato and amylomaize being more ordered on their outer regions. This could explain the high resistance of both these starches to enzyme hydrolysis.

Effect of tracheotomy tube occlusion on upper esophageal sphincter and pharyngeal pressures in aspirating and nonaspirating patients

The biomechanics of the pharyngeal swallow in patients with a tracheotomy tube were investigated with manometry. Upper esophageal sphincter (UES) and pharyngeal pressure recordings were made with and without occlusion of the tracheotomy tube. Criteria for selection were ability to tolerate tracheotomy tube occlusion for both 5 minutes prior to and during the first manometric analysis, absence of surgery to the upper aerodigestive tract other than tracheotomy, and no history of oropharyngeal cancer or stroke. Aspiration was determined objectively by fiberoptic endoscopic evaluation of swallowing (FEES) immediately prior to manometric recording. Eleven adult individuals with tracheotomy participated; 7 swallowed successfully and 4 exhibited aspiration on FEES. The results indicated no significant effect of tracheotomy tube occlusion on UES or pharngeal pressures in either aspirating or nonaspirating patients. It was concluded that the biomechanics of the swallow as determined by UES and pharyngeal manometric pressure measurements were not changed significantly by tracheotomy tube occlusion in aspirating or nonaspirating patients. These results support previous observations that subjects either aspirated or swallowed successfully regardless of tracheotomy tube occlusion status.

Oxygen therapeutics--current concepts

PURPOSE

In an effort to develop agents that enhance the oxygen-delivery capability of blood without the risks associated with allogeneic blood transfusions, several products are undergoing development and clinical trials. These oxygen transport agents can be divided into two main groups, perfluorocarbon (PFC) emulsions and modified hemoglobin solutions.

SOURCE

Articles from the literature on the development and clinical trials of oxygen therapeutic agents were reviewed.

PRINCIPAL FINDING

PFCs are synthetic fluorinated hydrocarbons that increase dissolved oxygen in the fluid phase of the blood without binding the oxygen molecule. They enhance oxygen delivery significantly and may be used to augment the technique of intraoperative autologous donation. Two PFC products have been tested in Phase III clinical trials. Hemoglobin-based oxygen carriers (HBOCs) are either cross-linked or microencapsulated hemoglobin molecules. Modification of the human hemoglobin molecule with intra- and inter-molecular cross-linking eliminates renal toxicity and improves the oxygen dissociation characteristics of the molecule. These modifications are necessary because stroma-free hemoglobin (Hb) does not release oxygen in the physiologic range and dissociates into dimers which can be rapidly filtered by the kidney, leading to renal toxicity. In addition to human Hb, bovine hemoglobin is another source of raw material for HBOC products. Recombinant human Hb has also been produced, using an E. coli expression system, for HBOC manufacturing. Four cross-linked hemoglobin products have been tested in Phase III clinical trials.

CONCLUSION

While no product has yet been approved for clinical use, preliminary studies with oxygen therapeutics show promising results, with effective oxygen carrying capacity and acceptable side effect profiles. In the future, the formation of a hybrid product which combines the best features from several of the products currently undergoing development may yield the ideal oxygen therapeutic agent.

Maillard reaction causes suppression of virulence gene expression in Listeria monocytogenes

Many environmental signals affect the expression of virulence genes of the food borne pathogen Listeria monocytogenes. In addition media composition has been shown to suppress levels of haemolytic activity. Using a Pr(plcA)::luxAB reporter gene fusion it was observed that the heat processing of media also reduces the level of virulence gene expression in L. monocytogenes without affecting its growth. Physicochemical factors that are considered to enhance the Maillard reaction were also found to increase the levels of suppression. The results indicate that heat treatment of a multicomponent matrix gives rise to specific inhibitors of the Listeria virulence gene operon.

Intraoperative physiologic variables and outcome in cardiac surgery: Part I. In-hospital mortality

BACKGROUND

Risk stratification schemes have been developed to predict outcome of coronary artery bypass grafting (CABG) procedures, which are predominately based upon unalterable preoperative patient characteristics. The purpose of this study was to determine if minimum intraoperative hematocrit, maximum glucose concentration, mean arterial pressure on cardiopulmonary bypass, or duration of bypass influence risk-adjusted in-hospital mortality after CABG.

METHODS

Outcome data from 2,862 CABG patients were merged with intraoperative physiologic data. A preoperative mortality risk index was calculated for each patient. Variables found significant (p<0.05) by univariate logistic regression were tested in a multiple variable model to determine risk-adjusted association with mortality.

RESULTS

Overall mortality rate was 1.85%. The preoperative risk index was significantly associated with mortality (p = 0.0001). No significant association was present between mortality and intraoperative variables. Preexisting hypertension was an independent predictor of mortality after controlling for risk index and bypass duration.

CONCLUSIONS

Preexisting hypertension proved to be an independent predictor of mortality in our patient population. This study found no evidence to support the hypothesis that mean arterial pressure less than 50 mm Hg, lower hematocrit, or elevated glucose while on bypass increases in-hospital mortality.

Intraoperative physiologic variables and outcome in cardiac surgery: Part II. Neurologic outcome

BACKGROUND

The impact of alterable physiologic variables on neurologic outcome after coronary artery bypass grafting procedures is unknown. The purpose of this study was to determine whether minimum intraoperative hematocrit, maximum glucose concentration, or mean arterial pressure during cardiopulmonary bypass influences risk-adjusted neurologic outcome after coronary artery bypass grafting.

METHODS

Outcome data from 2,862 patients undergoing coronary artery bypass grafting were merged with intraoperative physiologic data. A preoperative stroke risk index was calculated for each patient. Variables found significant by univariate logistic regression were tested in a multivariable model to determine association with outcome.

RESULTS

The incidence of stroke or coma in the study population was 1.3%. After controlling for stroke risk and bypass time, only an index of low mean arterial pressure during bypass retained a significant inverse association with outcome (p = 0.0304).

CONCLUSIONS

This study found no evidence that glucose concentration or minimum hematocrit are associated with major adverse neurologic outcome. The association between lower pressure during bypass and decreased incidence of stroke or coma persisted in all risk groups. This points to mechanisms other than hypoperfusion as the primary cause of neurologic injury associated with cardiac surgery.

Molecular flexibility profiling using NMR spectroscopy

Molecular flexibility is a factor that is not extensively studied in most pharmaceutical research efforts. When it is, the level of effort is high involving the preparation of detailed models supported by either molecular dynamics simulations and/or Nuclear Magnetic Resonance data. While these studies are both powerful and illuminating, they cannot be routinely applied in a drug discovery setting as they are time and expertise intensive. Yet there seems to be little doubt that at least in some cases, molecular flexibility plays a key role in complex formation. A simple, rapid and generally applicable flexibility profiling protocol was applied to two model systems and data describing the internal mobility of carbon atoms were obtained. The protocol utilizes the Model Free approach and NMR data to characterize the internal molecular dynamics of these compounds. The first model system consisted of fluorene and diphenylmethane where the anticipated flexibility trends were observed in the data providing a link between chemical intuition and the experimental results. Data on a second model system, which consisted of two Paclitaxel analogs, showed predictable patterns including dynamical phenyl and methyl groups and a relatively immobile taxane core. Subtle differences in the internal dynamics within the taxane core suggest that it cannot be considered as a rigid structure. Key advantages of using this approach are that no prior knowledge or supposition of dynamical features is required, the protocol can be carried out in most medicinal chemistry laboratories and the data obtained provide a common, empirically derived reference point to discuss the effects of molecular flexibility on activity.

Cellular uptake profile of paclitaxel using liquid chromatography tandem mass spectrometry

A new method for studying cellular uptake has been developed. This method is based on selected reaction monitoring liquid chromatography tandem mass spectrometry analysis of preparations from cell culture. The limit of detection for paclitaxel was approximately 0.1 microM intracellular concentration. This method has been utilized to study the uptake of paclitaxel and an analog (BMS-190616) in normal and multidrug resistant (MDR) cell lines. Paclitaxel and the analog, that had been noted to overcome MDR in animal models, were incubated with normal cells (HCT116) and MDR cells (HCT116(VM)46) at therapeutic concentrations. Intracellular drug concentrations were assayed at intervals from 0 to 1.0 h. Results show that paclitaxel accumulates to a level 12 times greater and BMS-190616 to a level 5 times greater in the normal cells as compared to MDR cells suggesting that paclitaxel is more sensitive to MDR than the analog. Furthermore, the steady state level of BMS-190616 was 4 fold greater than paclitaxel in the MDR cell line suggesting that at least part of this compound's increased therapeutic effect can be attributed to processes of uptake and efflux at the cellular level. These data show that the method is rapid, sensitive and presents a unique advantage over traditional radioisotopic methods in that it can readily be employed on a range of analogs without any additional synthetic effort.

Profiling degradants of paclitaxel using liquid chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry substructural techniques

A rapid and systematic strategy based on liquid chromatography-mass spectrometry (LC-MS) profiling and liquid chromatography-tandem mass spectrometry (LC-MS-MS) substructural techniques was utilized to elucidate the degradation products of paclitaxel, the active ingredient in Taxol. This strategy integrates, in a single instrumental approach, analytical HPLC, UV detection, full-scan electrospray MS, and MS-MS to rapidly and accurately elucidate structures of impurities and degradants. In these studies, degradants induced by acid, base, peroxide, and light were profiled using LC-MS and LC-MS-MS methodologies resulting in an LC-MS degradant database which includes information on molecular structures, chromatographic behavior, molecular mass, and MS-MS substructural information. The stressing conditions which may cause drug degradation are utilized to validate the analytical monitoring methods and serve as predictive tools for future formulation and packaging studies. Degradation products formed upon exposure to basic conditions included baccatin III, paclitaxel sidechain methyl ester, 10-deacetylpaclitaxel, and 7-epipaclitaxel. Degradation products formed upon exposure to acidic conditions included 10-deacetylpaclitaxel and the oxetane ring opened product. Treatment with hydrogen peroxide produced only 10-deacetylpaclitaxel. Exposure to high intensity ligh produced a number of degradants. The most abundant photodegradant of paclitaxel corresponded to an isomer which contains a C3-C11 bridge. These methodologies are applicable at any stage of the drug product cycle from discovery through development. This library of paclitaxel degradants provides a foundation for future development work regarding product monitoring, as well as use as a diagnostic tool for new degradation products.

Maillard induced complexes of bovine serum albumin--a dilute solution study

Association of bovine serum albumin (BSA) on heating in the presence and absence of 2% xylose has been studied using dynamic light scattering and sedimentation velocity. When 3% solutions of the protein alone are heated at 95 degrees C association products are formed with molar masses of approximately 2 x 10(6) g/mol, a value which is independent of the time of heating. These aggregates can be dissociated in solvents that disrupt non-covalent bonds. When the reducing sugar xylose is present there is a continuous change in the hydrodynamic properties with time. After 80 min a molar mass in excess of 7 x 10(6) g/mol is obtained. This increase in molar mass is attributed to additional non-disulphide linkages resulting from the Maillard reaction. Information about the gross conformation of the Maillard induced association products has been obtained from MHKS (Mark-Houwink-Kuhn-Sakarada) double logarithmic plots of D20,w and S20,w against molar mass. The values of the MHKS coefficients obtained are most consistent with a linear rod: i.e. the association is of an end-to-end type.