Sucrose and proton cotransport in Ricinus cotyledons

In Ricinus cotyledons, evidence for proton extrusion came from observation of direct acidification of the medium in the presence of potassium salts. Increasing K⁺ influx with increasing pH suggested a link between K⁺ influx and H⁺ efflux by an H⁺ pump. The kinetics of K⁺ influx and H⁺ efflux were consistent with a 1:1 stoichiometry K⁺:H⁺, which may indicate either electrical coupling or carrier mediated exchange. The results were consistent with an H⁺ pump setting up an electrochemical potential gradient which provides the driving force for an H⁺-sucrose cotransport and the movement of K⁺. With reference to this, a model for phloem loading is suggested.     

Reconstitution of sodium channels in large liposomes formed by the addition of acidic phospholipids and freeze-thaw sonication

Phosphatidylcholine (PC) alone or with phosphatidylethanolamine (PE) are sufficient for the reconstitution of Na+ channels in planar lipid bilayers. However, when Na+ channels were first reconstituted into liposomes using the freeze-thaw-sonication method, addition of acidic phospholipids, such as phosphatidylserine (PS), to the neutral phospholipids was necessary to obtain a significant toxin-modulated 22Na uptake. To further investigate the acidic phospholipid effect on reconstitution into liposomes, Na+ channels purified from Electrophorus electricus electrocytes were reconstituted into liposomes of different composition by freeze-thaw sonication and the effect of batrachotoxin and tetrodotoxin on the 22Na flux was measured. The results revealed that, under our experimental conditions, the presence of an acidic phospholipid was also necessary to obtain a significant neurotoxin-modulated 22Na influx. Though neurotoxin-modulated 22Na fluxes have been reported in proteoliposomes made with purified Na+ channels and PC alone, the 22Na fluxes were smaller than those found using lipid mixtures containing acidic phospholipids. Electron microscopy of negatively stained proteoliposomes prepared with PC, PC/PS (1:1 molar ratio), and PS revealed that the acidic phospholipid increases the size of the reconstituted proteoliposomes. The increment in size caused by the acidic phospholipid, due to the associated increase in internal volume for 22Na uptake and in area for Na+ channel incorporation, appears to be responsible for the large neurotoxin-modulated 22Na fluxes observed.     

Purification and substrate specificity of heparitinase I and heparitinase II from Flavobacterium heparinum. Analyses of the heparin and heparan sulfate degradation products by 13C NMR spectroscopy

The purification of two heparitinases and a heparinase, in high yields from Flavobacterium heparinum was achieved by a combination of molecular sieving and cation-exchange chromatography. Heparinase acts upon N-sulfated glucosaminido-L-iduronic acid linkages of heparin. Substitution of N-sulfate by N-acetyl groups renders the heparin molecule resistant to degradation by the enzyme. Heparitinase I acts on N-acetylated or N-sulfated glucosaminido-glucuronic acid linkages of the heparan sulfate. Sulfate groups at the 6-position of the glucosamine moiety of the heparan sulfate chains seem to be impeditive for heparitinase I action. Heparitinase II acts upon heparan sulfate producing disulfated, N-sulfated and N-acetylated-6-sulfated disaccharides, and small amounts of N-acetylated disaccharide. These and other results suggest that heparitinase II acts preferentially upon N,6-sulfated glucosaminido-glucuronic acid linkages. The total degradation of heparan sulfate is only achieved by the combined action of both heparitinases. The 13C NMR spectra of the disaccharides formed from heparan sulfate and a heparin oligosaccharide formed by the action of the heparitinases are in accordance to the proposed mode of action of the enzymes. Comparative studies of the enzymes with the commercially available heparinase and heparitinase are described.     

Mutagenic interactions between near-ultraviolet (365 nm) radiation and alkylating agents in Escherichia coli

The mutagenic interaction between near-ultraviolet (365 nm) radiation and the alkylating agents ethyl methanesulphonate (EMS) and methyl methanesulphonate (MMS) was studied in a repair-competent and an excision-deficient strain of Escherichia coli. Near-UV radiation modified the metabolic response of exposure to these chemicals and either reduced or increased their mutagenic efficiency. Based on these results, an experimental model was formulated to explain the mutagenic interactions that occur between near-UV and various agents that induce prototrophic revertants via error-prone repair of DNA. According to this model, low doses of near-UV provoke conditions for mutation frequency decline (MFD) and lead to a mutagenic antagonism. With increasing near-UV doses, damage to constitutive error-free repair systems increases, favouring the error-prone system and inhibiting the MFD. Under these conditions there will be a progressive decrease in antagonism until at high doses an enhancement of mutation frequency (positive interaction) will occur.     

PERFUSION FOR MYOCARDIAL REVASCULARIZATION WITHOUT AN ARTIFICIAL OXYGENATOR (New Method to Reduce Surgical Morbidity)

Thirteen patients were submitted to direct myocardial revascularization (saphenous vein graft) without the use of an artificial oxygenator. The perfusion was done by a left ventricle-to-aorta bypass and autogenous oxygenation. Most patients had three grafts implanted plus endarterectomy of the distal right coronary artery. There was one hospital death that was apparently not related to the method used. Perfusion time ranged from 45 minutes to 4 hours. Body temperature during perfusion was kept between 25 and 30 degrees C. Perfusion flow was maintained between 25 to 50 ml per kg of body weight per minute. Ischemic, hypothermic cardiac arrest was employed. We demonstrated for the first time that perfusion for this kind of heart surgery could be done with no artificial oxygenators and, apparently, is safer for the patients. There were no bleeding problems even in perfusions as long as 4 hours. There was no respiratory dysfunction, and artificial respiration was used for only 6 to 12 hours. The patients awoke at the end of surgery with no signs or symptoms of central nervous system damage, and vasopressor drugs were rarely used after surgery. Although the experience is very small, it suggests that many postoperative problems, especially those related to bleeding and respiratory dysfunction may be reduced or eliminated by this new method.     

Predictors of Condom Use among Peer Social Networks of Men Who Have Sex with Men in Ghana,West Africa

Ghanaian men who have sex with men (MSM) have high rates of HIV infection. A first step in designing culturally relevant prevention interventions for MSM in Ghana is to understand the influence that peer social networks have on their attitudes and behaviors. We aimed to examine whether, in a sample of Ghanaian MSM, mean scores on psychosocial variables theorized to influence HIV/STI risk differed between peer social networks and to examine whether these variables were associated with condom use. We conducted a formative, cross-sectional survey with 22 peer social networks of MSM (n = 137) in Ghana. We assessed basic psychological-needs satisfaction, HIV/STI knowledge, sense of community, HIV and gender non-conformity stigmas, gender equitable norms, sexual behavior and condom use. Data were analyzed using analysis of variance, generalized estimating equations, and Wilcoxon two sample tests. All models were adjusted for age and income, ethnicity, education, housing and community of residence. Mean scores for all psychosocial variables differed significantly by social network. Men who reported experiencing more autonomy support by their healthcare providers had higher odds of condom use for anal (AOR = 3.29, p<0.01), oral (AOR = 5.06, p<0.01) and vaginal (AOR = 1.8, p<0.05) sex. Those with a stronger sense of community also had higher odds of condom use for anal sex (AOR = 1.26, p<0.001). Compared to networks with low prevalence of consistent condom users, networks with higher prevalence of consistent condom users had higher STD and HIV knowledge, had norms that were more supportive of gender equity, and experienced more autonomy support in their healthcare encounters. Healthcare providers and peer social networks can have an important influence on safer-sex behaviors in Ghanaian MSM. More research with Ghanaian MSM is needed that considers knowledge, attitudes, and norms of their social networks in the development and implementation of culturally relevant HIV/STI prevention intervention strategies.     

Vaginal microbiome-hormonal contraceptive interactions associate with the mucosal proteome and HIV acquisition

Alterations to the mucosal environment of the female genital tract, such as genital inflammation, have been associated with increased HIV acquisition in women. As the microbiome and hormonal contraceptives can affect vaginal mucosal immunity, we hypothesized these components may interact in the context of HIV susceptibility. Using previously published microbiome data from 685 women in the CAPRISA-004 trial, we compared relative risk of HIV acquisition in this cohort who were using injectable depot medroxyprogesterone acetate (DMPA), norethisterone enanthate (NET-EN), and combined oral contraceptives (COC). In women who were Lactobacillus-dominant, HIV acquisition was 3-fold higher in women using DMPA relative to women using NET-EN or COC (OR: 3.27; 95% CI: 1.24–11.24, P = 0.0305). This was not observed in non-Lactobacillus-dominant women (OR: 0.95, 95% CI: 0.44–2.15, P = 0.895) (interaction P = 0.0686). Higher serum MPA levels associated with increased molecular pathways of inflammation in the vaginal mucosal fluid of Lactobacillus-dominant women, but no differences were seen in non-Lactobacillus dominant women. This study provides data suggesting an interaction between the microbiome, hormonal contraceptives, and HIV susceptibility.