Extracellular polysaccharides of the genusRhizobium

This paper reports an investigation of the extracellular polysaccharides produced by 26 strains ofRhizobium andAgrobacterium. Strains ofRhizobium leguminosarum andR. phaseoli produced a water-soluble polysaccharide containing glucose, glucuronic acid and 4-0-methylglucuronic acid. These substances were also identified in the polysaccharide of a single strain fromLotus uliginosus. Glucose was the only detectable component in the polysaccharide produced by strains ofAgrobacterium radiobacter andA. tumefaciens. The polysaccharides obtained from slow-growing rhizobia were not freely water-soluble. Glucose, mannose, rhamnose, galactose and 4-0-methylglucuronic acid were identified as components of this extracellular material.These results are related to previous studies on rhizobial taxonomy and to the infection process in legumes.     

Verapamil: a novel probe of surfactant secretion from rat type II pneumocytes

Surfactant from type II pneumocytes prevents the alveolar atelectasis found in both the neonatal and adult forms of respiratory distress syndrome. We have found that verapamil, a phenylalkene with calcium channel and alpha 1-receptor binding properties, has a multiphasic concentration effect on surfactant secretion from [3H]choline-labeled rat type II pneumocytes in culture. Verapamil (10(-8) M) caused a 24% stimulation of surfactant secretion, whereas an 8% inhibition was found at 10(-6) M and a 70% stimulation was found at 10(-4) M. Lactate dehydrogenase release occurred at 5 x 10(-4) M verapamil. Verapamil (10(-4) M) also produced a 100% increase in adenosine 3',5'-cyclic monophosphate (cAMP) in comparison with concentrations of less than or equal to 10(-6) M, an effect that could not be blocked by propranolol (10(-4) M). Verapamil (10(-6) M) increased the total formation of inositol phosphates (IP) by 23% in comparison with IP formation in control cells. Calcium influx was inhibited 15% by 10(-8) M verapamil and 37% by 10(-4) M verapamil. Calcium efflux was stimulated 44% by 10(-5) M verapamil. In combination with 50% effective concentrations (EC50) of terbutaline, phorbol ester, and ATP, the respective effects of verapamil (10(-4) M) on surfactant secretion were approximately additive. We conclude that verapamil has a novel multiphasic concentration effect on surfactant secretion, which appears to involve several signal transduction pathways including cAMP formation, IP formation, inhibition of calcium influx, and stimulation of calcium efflux.     

Estimation of the mitochondrial redox state in human skeletal muscle during exercise

The mitochondrial redox (NAD+/NADH) state can be used as a reflection of oxygen availability within the mitochondrion. Previous studies using isolated muscle preparations suggest that active muscle is not hypoxic during lactate production, whereas experiments with humans come to the opposite conclusion. Six men exercised for 5 min at 75% maximal O2 consumption (VO2max) and then at 100% VO2max to exhaustion. Ammonia, oxoglutarate (alpha-ketoglutarate), and glutamate, as well as lactate, were measured in biopsies (vastus lateralis) taken at the end of each exercise. The three former metabolites were used to determine the mass action ratio of glutamate dehydrogenase and thus were used as an estimate of the mitochondrial redox state. Muscle lactate increased (P less than 0.05) to 14.5 and 24.5 mmol/kg wet wt after 75 and 100% VO2max, respectively. At both exercise intensities, muscle ammonia rose (P less than 0.05), glutamate fell (P less than 0.05) to only 30-35% of rest levels, and oxoglutarate declined (P less than 0.05). Despite the high levels of muscle lactate accumulation, the estimated mitochondrial redox rate rose 300% (P less than 0.05) in both exercise bouts. This response should increase the activity of key oxidative enzymes and promote increased VO2. Furthermore the data do not support the concept that muscle lactate is formed because of tissue hypoxia.