Studies in human lactation 3: molybdenum and nickel in human milk during the first month of lactation

Molybdenum and nickel were measured in 62 and 46 samples, respectively, of human milk collected from 13 women between delivery and 38 d postpartum. Trace elements were analyzed by graphite-furnace atomic absorption spectrophotometry, with standard additions to whole milk without pretreatment. Molybdenum levels (mean +/- SD) fell from 15.0 +/- 6.1 ng/mL on day 1 to an apparently constant level of 1-2 ng/mL by 1 mo. Nickel concentrations did not change with time; the overall mean was 1.2 +/- 0.4 ng/mL. Intakes of the elements by infants were calculated with test-weighing data on the fully breast-fed infants of these same mothers. By 1 mo, the average daily intake of molybdenum was 1.5 micrograms; that of nickel was 0.8 microgram.

Diurnal and within-feed variations in lipase activity and triglyceride content of human milk

This study examined the diurnal and within-feed variations in the two lipases of human milk, bile-salt-stimulated lipase (BSSL) and lipoprotein lipase (LPL). In addition, all milks were also analyzed for triglyceride content. As compared to BSSL, LPL activity was more variable both among mothers and among different samples from the same mother (largest variation, 0-2.8 U/ml milk). The only significant variation in lipase activity was in LPL activity during a 24-h period (0.96 +/- 0.113, 0.52 +/- 0.21, and 0.57 +/- 0.092 U/ml milk at 0801-1600, 0001-0800, and 1601-2400 h, respectively) (p less than 0.05). Triglyceride content showed no significant diurnal variation but did increase significantly during a single feeding (31 +/- 9.4, 52 +/- 11.7, and 72 +/- 14.8, mumoles triglyceride/ml milk for fore-, mid-, and hind-milks, respectively) (p less than 0.05). There was no correlation between either LPL or BSSL activity and triglyceride content of the milks. Our data indicate that milk obtained for banking or research purposes will contain similar levels of BSSL activity irrespective of diurnal or within-feed timing of milk collections.

Nutrient intake by breast-fed infants during the first five days after birth

The intakes of milk and specific nutrients during the first 120 hours after birth were measured in 11 full-term, breast-fed infants. Infants were test weighed at all feeds using an electronic balance, and milk samples were obtained from both breasts one to three times daily. Milk was analyzed for levels of fat, protein, lactose, calcium, sodium, and potassium; energy content was calculated using the Atwater factors. The average (+/- SD) intake of milk in the first 24 hours after birth was 13 +/- 16 g/kg (range, 3 to 32 g/kg), increasing to 98 +/- 47 g/kg (50 to 163 g/kg) and 155 +/- 29 g/kg (110 to 196 g/kg) on days 3 and 5, respectively. Mean daily intakes of energy, lactose, calcium, and potassium were less than 12% of the mean day 5 intake on day 1 and less than 25% of the day 5 intake on day 2. In the first few days after birth, the nutrient intake of the solely breast-fed infant is highly variable and is frequently low.

Lipid composition of prepartum human mammary secretion and postpartum milk

Changes in lipid composition of mammary secretions of five women were studied at two prepartum periods and compared with composition of colostrum, transitional, and mature human milk. Fat content was approximately 1 g/dl during early (-42.0 days before parturition) and late (-9.5 days) prepartum periods and increased to 3-4 g/dl in colostrum (3.0 days post partum), transitional (7.2 days), and mature milk (56.2 days). Most of the lipid present was triglyceride either pre- (93%) or post- (97%) partum. All fat globule core lipids, with the exception of 1,3-diglycerides, increased from prepartum concentrations to levels usually found in milk. Prepartum secretions contained higher amounts of the membrane components, phospholipid (3.2 g/dl), cholesterol (2.3 g/dl), and cholesteryl ester (1.1 g/dl), which declined postpartum to 0.65, 0.37, and 0.09 g/dl, respectively. Thus, the content of core lipids exhibited an opposite pattern to the content of membrane lipids pre- and postpartum. With regard to synthesis of fatty acids, prepartum secretory mechanisms appeared to be very similar to those occurring postpartum since fatty acid composition of prepartum secretions closely resembled that of postpartum milk.

Determination of total protein in human milk: comparison of methods

We evaluated four spectrophotometric methods for suitability in determining total protein in human milk samples. Results were compared with those by an established method for the determination of total nitrogen (micro-Kjeldahl). Values for total protein by all four methods significantly correlated with micro-Kjeldahl. For the biuret assay, Lowry-Peterson assay, Bio-Rad Coomassie Blue assay, and Pierce BCA assay, the correlation coefficients were 0.96, 0.97, 0.89, 0.99, respectively. We also assessed the sensitivity of each assay to several purified human milk proteins. The Pierce BCA assay showed the least difference in values among different types of protein. For this reason, and because it showed the greatest precision (with acceptable constant and proportional error), we recommend the BCA method.

Determination of total protein in human milk: comparison of methods

We evaluated four spectrophotometric methods for suitability in determining total protein in human milk samples. Results were compared with those by an established method for the determination of total nitrogen (micro-Kjeldahl). Values for total protein by all four methods significantly correlated with micro-Kjeldahl. For the biuret assay, Lowry-Peterson assay, Bio-Rad Coomassie Blue assay, and Pierce BCA assay, the correlation coefficients were 0.96, 0.97, 0.89, 0.99, respectively. We also assessed the sensitivity of each assay to several purified human milk proteins. The Pierce BCA assay showed the least difference in values among different types of protein. For this reason, and because it showed the greatest precision (with acceptable constant and proportional error), we recommend the BCA method.

Insensible weight loss in children under one year of age

A selected group of 12 breast-fed infants were studied for insensible weight loss over the first year life. The method used to determine the insensible weight loss was non-invasive and based on a computerized weighing system. Findings indicate that the insensible weight loss in a one-year-old child reaches 36% of the average insensible weight loss reached in adulthood (360 g/day). Furthermore, the insensible weight loss (g/h/kg) was constant at about 1.9 g per kilogram per hour over the first year of life. Insensible weight loss contains two components, insensible water loss (92%) and metabolic losses (8%).

Studies in human lactation: zinc, copper, manganese and chromium in human milk in the first month of lactation

Zinc, copper, manganese and chromium were measured in a total of 259 samples of human milk from 11 women from day of delivery to 31 days postpartum. Milk intakes by their fully breast-fed infants were calculated from 24-h test-weighing measurements. Zinc was analyzed by flame atomic absorption spectrophotometry, and the other elements by graphite furnace atomic absorption. Mean (+/- SD) concentrations declined from a maximum of 11.5 +/- 4.7 micrograms/ml at 2 days to 2.98 +/- 0.78 micrograms/ml at 28 +/- 3 days. Changes in the other three elements were irregular. The average copper concentration declined from 0.6 +/- 0.12 micrograms/ml on day 5 to 0.41 +/- 0.04 micrograms/ml at 28 days. Manganese levels decreased from a mean of 5.4 +/- 1.6 ng/ml on day 1 to 2.7 +/- 1.6 ng/ml on day 5; from 8 to 28 days there was little change, the overall mean being 3.7 +/- 2.2 ng/ml. The average concentration of chromium over the whole period was 0.27 +/- 0.10 ng/ml. Average daily intakes of the elements, by the infants, over the one month period were: zinc, 2.0 mg; copper, 0.25 mg; manganese, 2.0 micrograms; chromium, 150 ng.

Sodium and potassium distribution in the lactating mouse mammary gland in vivo

The ratio of intracellular potassium to sodium in the mammary cells of the lactating mouse was compared with the ratio of potassium to sodium in the mouse milk to determine whether the sodium and potassium concentrations in milk are governed by a Donnan equilibrium as postulated earlier (Peaker 1977a, 1978). An efflux technique was used to determine the average intracellular sodium of 23.0 +/- 1.2 mumol/g tissue (+/- S.E. of mean). The intracellular potassium, determined by calculating the amount of potassium contained in both the interstitial and milk spaces and subtracting these values from the total tissue potassium, was 62 +/- 1 mumol/g tissue. The mean intracellular potassium to sodium ratio, calculated from individual efflux experiments, was 2.7 +/- 0.2. The total, interstitial, and milk water spaces were measured by tissue drying, sodium efflux, and lactose efflux, respectively. The average values (+/- S.E. of mean) obtained were 0.700 +/- 0.004 ml/g tissue, 0.150 +/- 0.016 ml/g tissue and 0.064 +/- 0.004 ml/g tissue. Based on these values the intracellular water space was 0.49 +/- 0.02 ml/g tissue. Intracellular concentrations of sodium and potassium calculated from the intracellular amounts of sodium and potassium and intracellular water space were 47 +/- 3 mM and 129 +/- 5 mM, respectively. The concentrations of potassium and sodium in mouse milk were 47 +/- 1 mM and 26 +/- 1 mM. The mean potassium to sodium ratio (+/- S.E. of mean) calculated from individual milk samples was 1.8 +/- 0.1. The milk ratio of potassium to sodium is significantly different (P less than 0.001) from the intracellular water ratio of potassium to sodium. This finding, in a tight epithelium such as the lactating mouse mammary gland, suggests that both sodium and potassium cannot be distributed passively across the apical membrane and an active transport process must exist for one or both of these ions in this membrane.

Studies on human lactation. I. Within-feed and between-breast variation in selected components of human milk

Within-feed and between-breast differences in the concentrations of sodium, potassium, chloride, calcium, magnesium, lipid, protein, lactose, glucose, urea nitrogen, creatinine, zinc, and copper were examined in milk samples from 10 women. The average lipid content doubled in the interval from the beginning of the feed to the end. The composition of the aqueous phase of milk, as determined by the major osmotically active constituents, did not vary significantly within the feed. For these components as well as for lipid a small mid-feed sample of milk gave the same mean composition as the pooled, pumped contents of one breast suggesting that such a sample is adequate for determination of milk composition in population studies. Sporadic, inconsistent differences in the composition of the milk from the right and left breasts were observed. It is suggested that mastitis may contribute to these differences. It is recommended that samples routinely be taken from both breasts and analyzed for sodium and chloride to rule out episodes of mastitis or other local phenomena which sporadically alter milk composition.

Accuracy of single- and two-feed test weighing in assessing 24 h breast milk production

The breast milk intake at a single feed (one-feed method) or the mean intake at two feeds (two-feed method) multiplied by the number of feeds per day was compared with the results of test weighing at every feed during a 24 h period. Six subjects were followed longitudinally from days 1-9 and 21-56 postpartum and the data analyzed by linear regression. There was a reasonable relationship between the mean values for milk intake obtained from the one- and two-feed methods and the 24 h test weights between days 3 and 9 of lactation. However, there was no relationship in full lactation (days 21-56). During both time periods, individual values for the one- and two-feed methods were associated with a large unsystematic error. The one- and two-feed methods may be useful only in situations where mean milk intake for a large population is desired and 24 h test weighing is not possible.

Measurement of steady state protein degradation in cultured human muscle cells

Double label techniques for measurement of protein turnover in cultured cells are described. In the isotope withdrawal method protein in cultured muscle is labeled with two isotopes of the same amino acid for 24 to 100 h, followed by exposure to fresh medium containing one isotope only at the same specific activity for an additional 24 to 48 h. In the isotope addition method the order of addition of single and double-labeled media is reversed. After incubation the ratio of the two isotopes in the cell protein is a function of the incubation time and the degradation rate constant KD; KD can readily be calculated using a graphical or iterative method. In mixed cultures of human muscle with initial incubation ranging 24 to 159 h, the KD's obtained from various incubation times were similar. Both the isotope withdrawal and the isotope addition methods gave a KD value of 0.018 h-1 similar to values obtained by two different single isotope methods which monitor the appearance of free isotope in the medium of previously labeled cells. There were no differences of KD values obtained in cultures of muscle from normal patients and those with denervation, inflammatory myopathies, or nonspecific myopathic biopsy changes. When proteins were separated by gel electrophoresis, those of molecular weight greater than 60,000 had higher average KD values as compared to lower molecular weight proteins. The double isotope labeling method has the advantage of being easily applied to cultures with small numbers of cells and is potentially useful in obtaining the degradation rates of individual cellular proteins. The major disadvantages are (1) in their present form the methods can be used only in steady state cultures and (2) they require rather long (24 h) labeling times.

Ionized calcium in human milk determined with a calcium-selective electrode

We measured the concentration of ionized calcium in human milk with a Radiometer ionized calcium analyzer at 37 degrees C. This instrument is designed to use simultaneous outputs from a pH electrode and a calcium ion-selective electrode to obtain the true ionized calcium in blood plasma. Because both the ionic strength and the pH of human milk differ significantly from that of plasma, we used a calibration curve that corrected for these variables. No other substances in milk interfered with the electrode response to Ca2+. The Ca2+ concentration of milk decreased and the pH increased as CO2 was lost to the atmosphere. Samples collected in glass capillaries, which minimized CO2 loss, contained 2.84 (SD 0.56) mmol of Ca2+ per liter at pH 6.98. We emphasize the importance of maintaining physiological CO2 concentrations when Ca2+ is being measured in milk.

Ionized calcium in human milk determined with a calcium-selective electrode

We measured the concentration of ionized calcium in human milk with a Radiometer ionized calcium analyzer at 37 degrees C. This instrument is designed to use simultaneous outputs from a pH electrode and a calcium ion-selective electrode to obtain the true ionized calcium in blood plasma. Because both the ionic strength and the pH of human milk differ significantly from that of plasma, we used a calibration curve that corrected for these variables. No other substances in milk interfered with the electrode response to Ca2+. The Ca2+ concentration of milk decreased and the pH increased as CO2 was lost to the atmosphere. Samples collected in glass capillaries, which minimized CO2 loss, contained 2.84 (SD 0.56) mmol of Ca2+ per liter at pH 6.98. We emphasize the importance of maintaining physiological CO2 concentrations when Ca2+ is being measured in milk.

Secretion of calcium into milk: review

Milk calcium exists in bound and ionized forms. Bound calcium is associated both with casein micelles and complexed to citrate and phosphate. Ionized calcium in milk is 1 to 4 millimolar, at least 1000 times its postulated concentration in the mammary alveolar cell. For this reason active transport mechanisms are necessary for transfer of this nutrient to the lumen of the mammary alveolus. Evidence that the major active transport system is a calcium adenosine triphosphatase residing in the membrane of the Golgi secretory vesicle is summarized. This adenosine triphosphatase appears to be activated by calcium concentrations in the micromolar range, to require magnesium ions, and to operate by phosphorylation of a 100,000 dalton enzyme intermediate. Metabolic processes are required to maintain a low concentration of calcium within the cytosol of the mammary alveolar cell. Because no evidence for sodium/calcium exchange could be found in the mammary gland of the lactating mouse, we suggest that these processes operate through a calcium adenosine triphosphatase in the basolateral membrane of the cell. Decreased calcium in the alveolar lumina decreased the integrity of the barrier between blood and milk. It is postulated from observations in other secretory systems that an increase in cystolic activity calcium may play a role in lactogenesis.

Calcium fluxes in mouse mammary tissue in vitro: intracellular and extracellular calcium pools

1. The total Ca content of the mammary gland increased from about 2 to 12 mumole/g tissue during the transition from pregnancy to lactation in the mouse. In tissue from lactating mice at least two thirds of the total Ca exchanged with external Ca in 6 hr. There was little non-exchangeable Ca in tissues from pregnant mice.2. At 37 degrees C the time courses of influx and efflux of (45)Ca in lactating tissues could be analysed by assuming three exponential components with rate constants of about 0.3, 0.06 and 0.005 min(-1) and containing, respectively, 1.7, 1.5 and 4.7 mumole (45)Ca/g tissue at the steady state.3. The rapidly effluxing component showed the time- and temperature-dependence characteristic of bulk-phase-limited diffusion through the extracellular space. The diffusion coefficient was about one quarter of the self-diffusion coefficient of Ca in aqueous solution, consistent with a tortuosity factor of about 2. A portion of the Ca in this component was displaced by La(3+). The amount remaining in the presence of 3 mm-La(3+) was close to that expected for free extracellular Ca. The rapid component was therefore interpreted as originating from an extracellular compartment containing both free and bound Ca.4. The rate of efflux of the intermediate component was slowed by a factor of ten when the temperature was decreased from 37 to 0 degrees C giving a Q(10) of 2.7, expected for membrane transport. The slow component present at 37 degrees C was not displaced by EGTA or La(3+), suggesting that it is not localized extracellularly. It was not apparent in the 0 degrees C efflux curves.5. The biphasic time course of uptake of ionophore (A23187)-releasable (45)Ca in particulate fractions obtained by homogenization and centrifugation of tissues which had been incubated with the isotope was consistent with the hypothesis that the two slower components of (45)Ca flux originate from intracellular compartments. Mitochondrial uptake probably did not contribute significantly to Ca exchange in these tissues.6. (45)Calcium fluxes in mammary tissues from pregnant mice also showed three components with rate constants similar to those found in tissues from lactating mice. The amount of Ca in each component was much smaller than in lactating tissue when compared on the basis of tissue weight.7. We conclude from these studies that: (i) intra- and extracellular Ca pools in mammary tissue can be distinguished on the basis of the temperature dependence of their fluxes and (ii) the transition from pregnancy to lactation is accompanied by large increases in both intra- and extracellular Ca pools in mammary alveolar cells.

ATP-dependent calcium transport by a Golgi-enriched membrane fraction from mouse mammary gland

Crude particulate preparations from the mammary glands of lactating mice were shown to transport calcium against a concentration gradient in the presence of ATP and mitochondrial inhibitors. Density gradient centrifugation with both sucrose and Percoll gradients indicated the presence of ATP-dependent transport in more than one membrane fraction. A Golgi-enriched membrane fraction possessed the highest specific activity of calcium transport. Digitonin, which increases the permeability of plasma membranes to calcium, did not affect this process. The Golgi fraction contained a 100,000 Dalton protein whose phosphorylation by gamma-[32P]-ATP was enhanced by a micromolar concentrations of free calcium. The phosphorylation was acid-stable and hydroxylamine-sensitive. These properties suggest that Golgi membranes in an activity secreting mammary epithelium possess a calcium transport system which resembles the calcium ATPase present in the sarcoplasmic reticulum of skeletal muscle.

Ionized calcium in milk and the integrity of the mammary epithelium in the goat

1. Injection of citrate or EGTA solutions into the lumen of the mammary gland of goats in quantities sufficient to reduce ionized calcium to less than one-tenth of normal, led to increases in milk concentrations of Na and Cl and decreases in K and lactose. 2. Subsequent milk yields were decreased in glands treated with citrate but not in those treated with EGTA. 3. Blood-milk potential difference decreased (i.e. towards zero) in glands in which citrate was present. 4. In goats milked hourly with the aid of oxytocin, milk Na and Cl concentrations increased while K and lactose decreased; there was no apparent decrease in Ca2+ concentration. 5. It is suggested that ionized calcium in milk is essential to preserve the integrity of the mammary epithelium during lactation.

K+ influx components in ascites cells: the effects of agents interacting with the (Na+ + K+)-pump

Several agents known to interact with the (Na+ + K+)-pump were tested for their effects on the components of steady-state K+ flux in ascites cells. 86Rb+ was used as a tracer for K+, and influx was differentiated into a ouabain-inhibitable "pump" component, a Cl--dependent and furosemide-sensitive "exchange" component, and a residual "leak" flux. All agents tested (ouabain, quercetin, oligomycin, phosphate) affected both the "pump" flux and the Cl--linked flux. These findings suggest a linkage between the activity of the Na/K ATPase and the Cl--dependent K+ exchange flux. In the discussion we point out that the mechanism of this linkage could be direct; e.g., Cl--dependent exchange may represent a mode of operation of the Na/K ATPase. However, data from this and other systems tend to suggest an indirect linkage between the Na+ pump and a KCl symporter, perhaps via a change in the level of intracellular ATP.

The secretion of calcium and phosphorus into milk

1. The time course of appearance of radioactivity in milk was studied following close-arterial infusion of labelled phosphate, Ca or leucine into the mammary artery of lactating goats. Maximum activities were reached at 1.5 hr in all milk fractions including inorganic soluble phosphate, inorganic colloidal phosphate, casein P, soluble Ca, protein-associated Ca and casein. 2. At 0.5 hr, labelling of the soluble and colloidal phosphate fractions was significantly higher than that of the casein P. 3. Recovery of 32P or 47Ca 3 or more hours after infusion into the cistern of the mammary glands was 98% or greater, indicating that the mammary epithelium is virtually impermeable to [32P]phosphate and 47Ca in the milk to blood direction. 4. Ca and P failed to enter milk in excess of the normal secretion rate when the milk was diluted with isosmotic sucrose given by intraductal injection. 5. These data suggest that milk Ca and phosphate in their various forms are secreted, like protein and lactose, by exocytosis of Golgi vesicles. Unless a paracellular pathway is present, as in oxytocin-treated animals, the milk concentrations are maintained by virtue of the impermeability of the mammary epithelium to these substances.

Antianaphylactic agents. 1. 2-(Acylamino)oxazoles

The synthesis and biological properties of 35 2-(acylamino)oxazoles are described. The majority of the compounds inhibit the release of slow-reacting substance of anaphylaxis (SRS-A) in vitro from sensitized guinea pig chopped lung. In addition, several of the compounds inhibited the release of SRS-A from passively sensitized human chopped lung and protected guinea pigs from the effects of anaphylaxis in a modified Herxheimer test.

Extracellular space of frog skeletal muscle in vivo and in vitro: relation to proton magnetic resonance relaxation times

1. The Na and Cl distribution spaces of freshly isolated frog muscles are 16.7 and 12.6%, respectively. These values increase to 25.6 and 23.3%, respectively, on incubation. 2. The extracellular components of both Na and Cl efflux curves are significantly smaller in freshly isolated muscles (approximately 12%) than in incubated muscles (approximately 18%). The fast exchanging A component of the extracellular space is increased more by incubation than the more slowly exchanging B component. 3. The proton magnetic resonance (p.m.r.) transverse relaxation curve for the water of freshly isolated frog muscles did not show the long, slowly relaxing tail present in curves from muscles incubated in Ringer solution. 4. When muscles were incubated in hypertonic solutions the p.m.r. transverse relaxation curves could be resolved into three components whose sizes were consistent with the components present in the sodium and chloride efflux curves. The non-exponentiality of the p.m.r. transverse relaxation curve therfore appears to arise from water in both the A and B extracellular compartments of muscle. 5. Efflux analysis indicated that the cellular Na content of both freshly isolated and incubated frog muscle is similar to that predicted by others (Lev, 1964; Armstrong & Lee, 1971; Lee & Armstrong, 1974) from measurements of intracellular Na ion activity using Na-sensitive micro-electrodes. The remainder of the tissue Na was found in the more rapidly exchanging extracellular compartments. The results of these experiments are inconsistent with the presence of a substantial fraction of bound Na in frog muscle. 6. These experiments show that muscle extracellular space is smaller in vivo than in vitro. Efflux analysis is suggested as the most accurate method of assessing extra-cellular components.

The extracellular compartments of frog skeletal muscle

1. Detailed studies of solute efflux from frog sartorius muscle and single muscle fibres were carried out in order to characterize a 'special region' (Harris, 1963) in the extracellular space of muscle and determine whether this 'special region' is the sarcoplasmic reticulum. 2. The efflux of radioactive Na, Cl, glusose, 3-O-methylglucose, xylose, glycine, leucine, cycloleucine, Rb, K, inulin (mol. wt. 5000) and dextran (mol. wt. 17,000) from previously loaded muscles was studied. In all cases except dextran the curve had three components, a rapid (A) component which could be equated with efflux from the extracellular space proper, a slow (C) component representing cellular solute and an intermediate (B) component. The distribution space for the B component was 8% of muscle volume in summer frogs and 12% in winter frogs and appeared to be equal for all compounds studied. We tested the hypothesis that the B component originated from the sarcoplasmic reticulum. 3. The C component was missing from the dextran curves. Both dextran and inulin entered the compartment of origin of the B component (compartment B) to the same extent as small molecules. 4. For all compounds studies, the efflux rate constant for the A component could be predicted from the diffusion coefficient. For the B component the efflux rate constant was 6--10 times slower than that for the A component but was still proportional to the diffusion coefficient for the solute in question. 5. When Na and sucrose efflux from single fibres was followed, a B component was usually observed. The average distribution space for this component was small, averaging 1.5% of fibre volume. There was no difference between the average efflux rate constants for Na and sucrose. 6. In an appendix, the constraints placed on the properties of a hypothetical channel between the sarcoplasmic reticulum and the T-system by the linear electrical parameters of frog skeletal muscle are derived. It is shown that the conductance of such a channel must be less than 0.06 x 10(-3) mohs/cm2 of fibre membrane. 7. The conductance between compartment B and the extracellular space can be calculated from the efflux rate constants for Na, K and Cl. The value obtained was 5 x 10(-3) mhos/cm2 of fibre membrane or 100 times the limiting value for the conductance of the T-SR junction. 8. The finding that there is a B component in the efflux curves for large molecular weight substances like inulin and dextran and the small size of the B component in efflux curves from single muscle fibres indicate that the 'speical region' of the extra-cellular space of frog muscle is not the sarcoplasmic reticulum. This conclusion is confirmed by a calculation of the conductance between the B compartment and the extracellular space. The value obtained is incompatible with predicted electrical properteis of the SR-T-tubule junction...

Antiprotozoal thiazoles. 2. 2-(5-Nitro-2-furyl-, thiazolyl-, and 1-methylimidazolyl-)thiazoles

Ten 2-substituted 4-thiazolecarboxaldehyde hydrazones bearing 5-nitro-2-furyl, 5-nitro-2-thiazolyl, and 1-methyl-5-nitro-2-imidazolyl functions have been prepared and screened for activity against Trypanosoma cruzi infections in mice. The results permitted the ranking of these substituents in decreasing order of activity: 1-methyl-5-nitro-2-imidazolyl greater than 5-nitro-2-furyl greater than 5-nitro-2-thiazolyl, the last being inactive. Some structural features of the side chain necessary for optimum activity are discussed. The most active compound, 4-[[[2-(1-methyl-5-nitro-2-imidazolyl)-4-thiazolyl]methylene]amino]thiomorpholine 1,1-dioxide, compared favorably with the standard Nifurtimox against three recent clinical isolates of T. cruzi, including one with a high myocardial tissue infiltration.

Spin-lattice relaxation times for 13C in isotope-enriched glycine accumulated in frog muscle

Spin-lattice relaxation times (T1's) of 13C-enriched glycine accumulated in frog muscles were determined at 1 degrees C by the inversion-recovery (180 degrees -tau-90 degree pulse sequence) method and compared with the values obtained in free solution. The value of T1 for the alpha-13C nucleus of glycine in the tissue was 50% of that obtained in free solution. The observed value for T1 in the tissue was not concentration-dependent, and no difference in chemical shift was observed between tissue and free solution. Quantification of the area under the glycine peak suggested that the observed signal represents at least 80% of the intracellular glycine. An average nuclear Overhauser enhancement of 2.83 for intracellular glycine indicates that the relaxation mechanism within the cell is predominantly dipolar, as in free solution. The value of T1 for the 13C' nucleus of glycine in the tissue was 67% of that in a solution of similar concentration. A quantitative analysis of the findings suggests that the observed difference in the value of T1 between tissue and free solution results from a difference in viscosity. The data provide no evidence either for special organization of intracellular water or for glycine binding. It is proposed that intracellular diffusion coefficients may be determined from measurements of 13C T1's of 13C-enriched intracellular solutes.

Control of amino acid transport in the mammary gland of the pregnant mouse

The regulation of the uptake of the amino acid analog alpha-aminoisobutyric acid was studied in diced mammary glands from pregnant mice. Stimulation of uptake by insulin was not prevented by inhibitors of protein synthesis; protein synthesis inhibitors decreased uptake by 20%; this response occurred more promptly in insulin-treated tissues. Elimination of extracellular amino acids led to a substantial increase in transport which was not abolished by inhibitors of protein synthesis. These results indicate that insulin does not increase amino acid transport in this system by altering synthesis and degradation of transport protein. They are consistent with a model in which the activity of the existing amino acid transport protein in subject to negative feedback regulation from the intracellular amino acid pool.

Amino acid accumulation in frog muscle. II. Are cycloleucine fluxes consistent with an adsorption model for concentrative uptake of amino acid?

Cycloleucine accumulation by frog muscle was studied at 0 degrees C and 25 degrees C. At external concentrations less than 5 mM the distribution ratio of cycloleucine is higher at 0 degrees C. At concentrations greater than 5 mM the converse is true due to apparent exclusion of cycloleucine from a larger portion of the cell water at 0 degrees C than at 25 degrees C. The steady state data are consistent with an adsorption model for amino acid accumulation. Flux studies provide a means to rule out this model if all the possible rate-limiting steps in the movement of amino acid into and out of the cell are considered. These steps include intra-cytoplasmic diffusion, desorption from cytoplasmic or membrane sites and passage through the cell membrane. The assumption is made that the rate-limiting step for influx and efflux is the same, allowing the use of either influx or efflux data to examine the model. Diffusion-limited flux is ruled out on the basis of "influx profile analysis" of the time course of cycloleucine entry at both 0 degrees C and 25 degrees C. At least 95% of all intracellular cycloleucine leaves frog muscle cells with a single exponential time course at both 0 degrees C and 25 degrees C. The rate constant of efflux does not vary with cellular concentration. These findings are shown to be incompatible with desorption-limited efflux. They are compatible with membrane-limited efflux only if (i) adsorption sites are located on membranes with direct access to the extracellular space and (ii) the rate constant for desorption is equal to the rate constant of membrane-limited efflux of free amino acid. It is considered unlikely that such a coincidence would occur at both 0 degrees C and 25 degrees C. Therefore, an adsorption model for cycloleucine accumulation in frog muscle appears to be untenable.

An electrogenic component of the potential difference in the rabbit lens

The normal resting potential of the rabbit lens, -70mV, is altered to -59mV by ouabain concentrations up to 5-1- minus 6M, and to -52mV at 4 degrees C. Ouabain acts only at the anterior lens surface. The temperature effect id completely reversible. The Hodgkin-Katz-Goldman equation can be used with the measured lens potentials and Na+ and K+ levels in the lens and bathing medium to obtain alpha, the ration of the membrane permeabilities to Na+ and K+. The alpha-values obtained were 0.052 at 4 degrees C and 0.053 in 5-10 minus 6M ouabain. These data suggest that the change in potential due to cold and ouabain is caused by an inhibition of an electrogenic Na+ ump in the anterior lens epithelium.

Nuclear magnetic resonance studies and water "ordering" in the crystalline lens

Nuclear magnetic resonance studies of the relaxation times of the water in the crystalline lens show that, as in all interfacial systems, these parameters are markedly reduced from their values in pure water, that T(2) is less than T(1), and that both depend on water content. Determination of diffusion coefficients and studies on physiologically inert lenses indicate that reduced relaxation times do not provide direct evidence for ordering of the bulk of the cell water.

Solute concentration gradients in frog muscles at 0 degree C: active transport or adsorption?

In isolated frog muscle that has been incubated for 7 days at 0 degrees C invitro K(+) and Na(+) remain at normal concentrations. Amino acids are accumulated against a concentration gradient at this temperature; for example, glycine accumulates in muscle to a concentration ten times that in the external solution. The amount of cycloleucine accumulated is greater at 0 degrees C than at 25 degrees C. These findings, which are difficult to explain on the basis of metabolically linked active transport, are Consiststent with the view that solute accumulation by cell is the result of adsorption on spesific sites.