In situ enclosure experiments on the influence of cultured mussels (Perna canaliculus) on phytoplankton at times of high and low ambient nitrogen

The influence of the cultured mussel Perna canaliculus (Gmelin 1791) on the abundance of phytoplankton was investigated in Pelorus Sound, New Zealand. Four in situ enclosure experiments were undertaken, two in summer when ambient nitrogen was low, and two in winter when it was high. Each experiment had four manipulation types: added mussels; added nitrogen; both mussels and nitrogen added; and control (no additions). In summer, there was a significant increase of chlorophyll a in response to added nitrogen, indicating that the phytoplankton were nitrogen-limited. At this time, mussels caused an increase (11-17%) in phytoplankton biomass, possibly by converting particulate nitrogen to ammonium, making the nitrogen available for phytoplankton utilisation. The highest ambient chlorophyll a concentrations coincided with high ambient nitrogen in the winter. At this time, mussel grazing caused a significant decrease (5-14%) in phytoplankton concentration, indicating that within-farm depletion of phytoplankton is most likely to occur in winter. On an annual time scale, the mussels had a stabilising influence on phytoplankton biomass, reducing high ambient levels in winter and slightly increasing low levels in summer.     

Intercellular junctions during development of the definitive kidney in lampreys: freeze fracture and morphometric analyses

The changing morphology of intercellular junctions in renal morphogenesis during lamprey metamorphosis was followed using freeze-fracture replicas and morphometry. Gap junctions and particle aggregates among strands of occluding junctions are conspicuous in the differentiating podocytes of the renal corpuscle and in the early ciliated neck and proximal segments but not in the distal segment. The cells of the segmented nephron arise from alpha nephrogenic cells which have a focal aggregate (macula occludens) of 4.8 junctional strands. Upon the initiation of metamorphosis the number of strands increases to 8 in undifferentiated cells with either maculae or zonulae occludentes. Differentiation of both neck and proximal segments is accompanied by gradual transformation of a 7-strand zonula occludens to a 4-strand junction but it becomes more shallow in the latter segment. Two types of undifferentiated cell are recognized through five of the seven metamorphic stages. Cells of two types of distal segments begin differentiation at the midpoint of transformation and immediately show zonula occludens of different morphology. Distal segment I (pars recta) has 5 strands and a 0.250 mum depth whereas segment II has 8-9 strands with twice the apical-basal depth. The larval archinephric duct undergoes a moderate transformation in junctional morphology with the addition of 2 strands and no increase in apical-basal depth in zonulae occludentes during metamorphosis. Changes and development of types of intercellular junctions along the nephron in lampreys are discussed with reference to known regional functional specialization in this organism and with the morphology of renal tubular intercellular junctions in other vertebrates.     

Aspartokinase I-homoserine dehydrogenase I of Escherichia coli K12 (lambda). Activation by monovalent cations and an analysis of the effect of the adenosine triphosphate-magnesium ion complex on this activation process.

The dehydrogenase activity of the aspartokinase I-homoserine dehydrogenase I complex isolated from Escherichia coli K12 is subject to a cooperative activation by K+ or Rb+, which is characterized by a Hill coefficient of approximately 2. Ionic strength has little effect on the Hill coefficient for this activation process; however, high ionic strength appears to increase the enzyme's affinity for K+ and decrease its affinity for Rb+. The Vmax of the K+-activated dehydrogenase is greater than that of the Rb+-activated dehydrogenase. The results of a study of the competition between K+ and Rb+ in the activation process suggest the presence of an activated species containing both K+ and Rb+. The cooperative activation by K+ is antagonized by Na+ via a process that is noncooperative with respect to Na+. The MgATP-2- complex, a substrate for the kinase activity of aspartokinase I-homoserine dehydrogenase I, has a marked effect on the K+ activation of the dehydrogenase activity. Kinetic studies of this effect of MgATP-2- on the K+ requirement of the dehydrogenase at pH 8.9 indicate that: (a) activation by a monovalent cation is essential in the presence as well as in the absence of MgATP-2-; (b) the concentration of K+ required to activate fully the dehydrogenase is reduced in the presence of MgATP-2-; (c) activation of the dehydrogenase by K+ is noncooperative in the presence of MgATP-2-; and (d) the maximum velocity for the dehydrogenase catalyzed oxidation of homoserine is greater in the presence of MgATP-2- than in its absence. Based on these results, a simple model consistent with these data is proposed. Destruction of the kinase activity and the threonine sensitivity of the aspartokinase-homoserine dehydrogenase complex by treatment with 5,5'-dithiobis(2-nitrobenzoic acid) or by incubation at pH 9 also converts the K+ activation of the dehydrogenase from a cooperative to a noncooperative process. Marked protection of the enzyme against loss of threonine sensitivity at pH 9 is afforded by MgATP-2- plus K+ and homoserine. The apparent molecular radius of the enzyme complex as determined by gel filtration at pH 8.85 in the presence of threonine or MgATP-2- plus K+ and homoserine is dependent on the enzyme concentration. The observed apparent molecular radii of 70 A at high enzyme concentrations and 61 A at low enzyme concentrations are consistent with the enzyme's undergoing a concentration-dependent dissociation from a tetrameric to a dimeri     

Nippostrongylus brasiliensis: further properties of antibody-damaged worms and induction of comparable damage by maintaining worms in vitro.

When adult Nippostrongylus brasiliensis were maintained in vitro they became damaged. Using the criteria of ultrastructural morphology, acetylcholinesterase isoenzyme pattern and the behaviour of the worms after transfer to a normal rat, this damage appeared to be similar to that produced by the in vivo action of antibodies. Antibodies were shown to be responsible for the anterior migration of adult worms which occurs during primary infections in mature rats and in the prolonged infections seen in lactating and immature rats. Antibody damaged worms and worms unaffected by antibodies were equally able to stimulate the immune response required for worm expulsion. Apparently antibody damage is not required for the initiation of the second immune component necessary for expulsion of this parasite.     

Oral amoxicillin in acute uncomplicated gonorrhea

Of 53 patients with acute uncomplicated gonorrhea treated with amoxicillin 2 g and probenecid 1 g orally as a single administration, six failed to return for follow-up examination, 10 developed postgonococcal urethritis and one was a treatment failure. The remainder achieved symptomatic cure in an average of 2.3 days. Adverse drug effects were infrequent, mild and transient. We conclude that this dose of amoxicillin and probenecid is a safe and effective treatment regimen.     

Effective vascular compliance and venous diameter in dogs.

Total effective vascular compliance was measured repeatedly in open-chest dogs without circulatory arrest, utilizing a closed-circuit venous bypass system with a constant cardiac output. Mutual inductance coils were used to measure the diameter of the inferior vena cava above the diaphragm at the position where the pressure change was recorded during a volume load (lambde V). In all experiments, there was a relationship which tended to be curvilinear between the diameter of the inferior vena cava and the venous pressure before lambde V. No relationship was demonstrated between the initial diameter or pressure and the calculated effective vascular compliance. During aortic constriction or infusion of noradrenaline, the effective compliance was reduced in value at any given initial venous diameter and pressure. An unaltered venous diameter and plasma volume excluded the possibility of a large change in initial venous volume as a cause of the observed changes in compliance during aortic constriction or during infusion of noradrenaline. A relationship was observed between compliance and calculated venous wall tension so that as the wall tension, developed during a fixed volume load, increased, there was an associated reduction in compliance. These results demonstrate that the measurement of effective compliance provides an assessment of combined active and passive venous wall tension and venous tone.     

Altered metabolism of ppGpp in quinone-treated E. coli: Possible role of aminoacyl-tRNA synthetases

The bacteriostatic quinone 6-amino-7-chloro-5,8-dioxoquinoline inhibits leucyl-tRNA synthetase in vivo and in vitro (Ogilvie et al. Biochim. Biophys. Acta $\text{407}$, 357–364; 1975). In this report it is shown that the quinone also interferes with the metabolism of ppGpp. Quinone treatment of E. coli MRE 600 causes the same phenotypic pattern as found in spoT^? mutants: overproduction of ppGpp and a drastic increase of its half-life; the formation of pppGpp, the possible degradation product of ppGpp, is blocked. A model is discussed to explain how the inhibition of leucyl-tRNA synthetase could account for the altered metabolism of ppGpp.     

Effects of estradiol and progesterone on accumulation of relaxin- and carbohydrate-containing granules in endometrial gland cells of the guinea pig

Guinea pigs were spayed and given various regimens of injections of estradiol and progesterone. The following were monitored in each animal: pubic separation (relaxin stimulation), resorption of the vaginal membrane (estrogen priming), and the presence of PAS-positive granules and/or relaxin in endometrial gland cells (EGC). Injections of estradiol alone resulted in resorption of the vaginal membrane, accumulation of PAS-positive granules in EGC of all animals, and accumulation of relaxin in EGC of two of four animals; but they did not cause pubic separation. Progesterone injections did not result in resorption of the vaginal membrane, separation of pubes, or accumulation of PAS-positive granules; however, one of three animals demonstrated a few EGC that contained relaxin. Animals that received both estradiol and progesterone exhibited PAS-positive granules and relaxin in EGC as well as separated pubes, but did not have resorbed vaginal membranes. Upon examination with the electron microscope, EGC from animals that received estradiol alone exhibited remarkable numbers of secretory granules that contained a carbohydrate-rich material. Secretory granules were not prominent in EGC from animals that received progesterone alone. Estradiol and progesterone injections resulted in accumulation of secretory granules in EGC that contained relaxin and a carbohydrate-rich material. The observations that estradiol and progesterone induce relaxin production in EGC support the hypothesis that uterine relaxin plays an important role in pregnancy and/or parturition in the guinea pig.     

Analysis of venous flow transients for estimation of vascular resistance, compliance, and blood flow distribution

We analysed venous flow transients using a long venous circuit and right heart bypass in 17 dogs after a rapid decrease in atrial pressure. A biphase curve was obtained which we decomposed into a two-compartment model, one with a fast time constant for venous return (0.069 min) and 52% of total circulating flow (Q), and one with a slower time constant (0.456 min) and 48% of Q. Subsequently, separate drainage from splanchnic and peripheral beds (with the renal venous return in the peripheral bed drainage) allowed comparison of time constants and venous outflow in these beds. The sum of the venous outflow volumes over time during separate drainage was indistinguishable from the single biphasic venous outflow volume curve over time observed with a long circuit and single reservoir. The fast time constant of the biphasic curve was not different from that determined by separate drainage from the peripheral circulation. The slow time constant of the single biphasic curve of 0.456 min was hybrid of two time constants, 0.216 min in the splanchnic bed and 0.862 min in the peripheral bed. Separate drainage from peripheral and splanchnic vascular beds demonstrated that the peripheral bed constituted 70% of venous outflow in the fast time constant compartment using Caldini's technique, whereas the splanchnic bed constituted 63% of venous outflow in the slow time constant compartment. It is concluded that, although Caldini's technique demonstrates biphasic venous flow transients, neither the fast nor the slow time constant compartments resolved from this analysis represent a particular anatomical region or vascular bed.