Nonsteady-State Three Compartment Tracer Kinetics: I. Theory

A set of differential equations is derived which describes the four unidirectional fluxes of a substance across the boundaries of the central compartment of a serially arranged three compartment system, and the amount of this substance present in the central compartment. An analytic solution is obtained which yields all of these quantities as functions of time. The analysis is associated with a defined set of repetitive experiments from which the necessary data are obtained and during which the two outer compartments must be subject to experimental control. The solution is applicable to both the initial steady state and a transient, time-dependent state created by making a step change in the initial conditions. It describes the fluxes and compartment size without assuming that constant kinetic coefficients relate the fluxes to compartmental quantities but is limited by the requirement that the response of the system be repeatable in time.     

The Kinetics of Sodium Transport in the Toad Bladder : II. Dual effects of vasopressin

In the accompanying paper, a compartmental model for the toad bladder sodium transport system was developed. In the present paper, the model is tested by determining the effects of antidiuretic hormone on the pools and fluxes. It is shown that this hormone affects only that sodium pool previously designated as the transport pool, and that the effects are on two separate sites. In the first place, the hormone stimulates entry at the mucosal side of the transport compartment, and by this means brings about an increase in the amount of sodium contained in the compartment. Second, the hormone has a distinct stimulatory effect on the rate coefficient for efflux across the serosal boundary, the pump rate coefficient. Evidence is presented that under control conditions, the pump rate coefficient is a decreasing function of the pool size, a characteristic feature of a saturating system. Therefore, the effect of vasopressin in increasing both the pool size and the pump rate coefficient must be construed as a direct effect on the pump, and not one which is secondary to the increase in the pool size. Furthermore, it is shown that the effect of the hormone on the sodium pump is not dependent on the presence of sodium in the serosal medium.     

The Kinetics of Sodium Transport in the Toad Bladder : I. Determination of the transport pool

A compartmental model of toad bladder sodium content has been developed, whereby it is possible to measure the four unidirectional fluxes across the opposite faces of the transport compartment, as well as the amount of sodium in the compartment. ²⁴Na is added to the mucosal medium of a short-circuited bladder mounted between halves of a chamber in which the fluid is stirred by rotating impellers. After a steady state is reached, nonradioactive medium is flushed through both sides of the chamber, collected, and counted. The data from each chamber are fitted to sums of exponentials and interpreted in terms of conventional compartmental analysis. Three exponentials are required, with half-times of 0.2, 2.2, and 14.0 min. It is shown that the first of these represents chamber washout, the second the transport pool, and the third a tissue compartment which is not involved in active sodium transport and which does not communicate with the transport pool. The second compartment contains 10.5 µEq of sodium per 100 mg dry weight, an amount equal to approximately 30% of total tissue sodium. The results also indicate, as expected from electrophysiological data, that the mucosal-facing side of the transport compartment is over 10 times as permeable to sodium as the serosal, or pump, side.     

The Coupling of the Short-Circuit Current to Metabolism in the Urinary Bladder of the Toad

The relationship of the short-circuit current to metabolism was studied in the toad bladder in vitro. Substrates and inhibitors were added to the bathing medium and the effect on the short-circuit current was determined. The spontaneous decline in the short-circuit current that occurred in substrate-free media was prevented or reversed by the addition of glucose, pyruvate, lactate, or β-hydroxybutyrate, whereas acetate and tricarboxylic acid cycle intermediates had no effect. A variety of metabolic inhibitors depressed the short-circuit current; depression by iodoacetate and by malonate was delayed by prior addition of pyruvate or lactate but not by glucose. The ability of a substrate to stimulate the current did not correlate with its rate of oxidation to CO₂. On the basis of earlier studies, the metabolic effects on the short-circuit current were assumed to reflect equivalent effects on the rate of active Na transport. It is suggested that the energy for Na transport is provided not by a general cellular metabolic pool but by a specific metabolic pathway or pathways spatially linked to the transport mechanism.     

The Synthesis of Ribosomes in E. coli: II. Analysis of the Kinetics of Tracer Incorporation in Growing Cells

Equations are derived representing the flow of radioactive tracer in a sequence of reactions. The conditions under which the equations are applicable are defined. A function ϕ, representing the newly synthesized fraction is defined, and its use in the analysis of precursor-product relationships is discussed.     

Kinetics of C-14 Translocation in Soybean: II. Kinetics in the Leaf

The kinetics of ¹⁴C-assimilates in the soybean leaf were studied in pulse labeling and steady state labeling experiments. ¹⁴C-Sucrose apparently served as the ultimate source, at least, of translocated ¹⁴C-sucrose. However, since the specific activity of leaf sucrose reached a maximum within 5 minutes after pulse labeling, whereas that of exported sucrose did not reach a maximum until at least 20 minutes, it appeared that there were two sucrose compartments in the leaf. A possible physical basis for the two compartments may be the mesophyll (a photosynthetic compartment) and a specialized “paraveinal mesophyll” (a nonphotosynthetic compartment), through which photosynthate must pass on its way to the veins.     

Biomass and Pigment Production in Three Isolates of Azolla II. Response to Light and Temperature Stress

Two isolates of Azolla caroliniana Willd. (RAR, M-3) and oneof Azolla filiculoides LAM. (LA) were compared and characterizedin defined growth environments. A moderate environment (200–230µ mol m^–2 S^–1, 18/6 h photoperiod and 26/22C thermoperiods) was selected to record growth in near-optimumconditions. All isolates doubled their fresh and dry weightsin approximately 2–3 d during the first week of trials.Acetylene reduction rates were low for all isolates, but RAR(from Amazonian Colombia) generally grew the fastest. RAR alsoaccumulated more chlorophyll, its chlorophyll doubling times(2.14 0.1 d) were 1–2 d faster than those of M-3 orLA, and it retained the most stable chlorophyll a/b ratios andtotal chlorophyll densities. Growth data for all isolates convergedduring the second week. Dry-weight doubling times were longerthan 3 d. None of the isolates excreted measureable amountsof nitrogen in month-long trials. Stress trials were conducted using high light (450–510µ mol m^–2 s^–1) and/or high temperature (35/31C conditions Biomass yields were usually least inhibited, ifat all, with elevation of only photon flux densities. High temperaturealone stimulated the dry-weight growth only of M-3 comparedwith its growth under moderate conditions. Biomass, chlorophyll,and acetylene reduction data suggested that M-3 may have a higheroptimum growth temperature than RAR or LA. The combined effectof light and temperature stress depressed acetylene reductionrates in RAR and M-3 to a greater extent than did either parameteralone. High light levels had more effect than high temperatures ininhibiting chlorophyll doubling times and inducing anthocyaninproduction in RAR and M-3. These two isolates did not form anyanthocyanin in elevated temperatures. Pre-incubation in darknessbefore exposure to elevated light/temperature conditions facilitatedanthocyanin production in all isolates. LA, however, provedto be the isolate most sensitive to stress by heat, alone oraugmented by light stress, according to all criteria used. Azolla caroliniana Willd., Azolla filiculoides Lam., biomass and chlorophyll accumulation, anthocyanin production, acetylene reduction, light/temperature stress     

Asymptomatic Significant Bacteriuria in the Non-pregnant Woman: II. Response to Treatment and Follow-up

Short courses of nitrofurantoin and ampicillin produced an immediate cure in 80% of adult non-pregnant bacteriuric women. Of the subjects so treated, 55% remained cured at the end of one year. Over the same follow-up period 36% of untreated bacteriuric women developed a spontaneous remission of bacteriuria. Treatment failed to prevent the development of symptomatic infection, and the reinfections which followed successful treatment were more commonly associated with the development of symptoms than the persistent or relapsing infections in untreated or unsuccessfully treated subjects.It is concluded that a search for bacteriuria in non-pregnant women is unlikely to be of value as a preventive measure, since in many instances it fails to detect urinary tract infection at an early stage and since treatment by methods suitable for large-scale use is ineffective.     

Wild Cane Toads (Rhinella marina) Expel Foreign Matter from the Coelom via the Urinary Bladder in Response to Internal Injury,Endoparasites and Disease

Dissections of >1,200 wild-caught cane toads (Rhinella marina) in tropical Australia confirm a laboratory report that anurans can expel foreign objects from the coelom by incorporating them into the urinary bladder. The foreign objects that we found inside bladders included a diverse array of items (e.g., grass seeds, twigs, insect prey, parasites), many of which may have entered the coelom via rupture of the gut wall. In some cases, the urinary bladder was fused to other organs including liver, fat bodies, ovaries, Bidder’s organs, lungs, mesentery, stomach wall, gall bladder, and the abdominal wall. Acanthocephalan parasites (of a range of developmental stages) were identified from the walls of the urinary bladders of three cane toads. This organ may play a significant role in destroying or excreting metazoan parasites, as well as inanimate objects.     

Extrusion of Sodium Ions by Barley Roots: II. Localization of the Extrusion Mechanism and its Relation to Long-distance Sodium Ion Transport

An active sodium effux hasbeen demonstrated in excised barleyroots. Isolated cortical and stelar tissues from the same materialdo not show any evidence of such an efflux mechanism. When intactbarley plantswere allowed to absorb ²²Na active sodium extrusionwas not observed, although the percentage of ²²Na transportedto the shoot was stimulated 20 to 40 percent by ouabain at 5x 10^–4 M. Absorption and long-distance transport of phosphatewas unaffected by ouabain at this concentration. Interpretationof these data lead to the conclusion.that the sodium-effluxpump in barley roots is located at or near the endodermis externalto the Casparian band. This pump thus provides a mechanism wherebysodium can be partially excluded from the shoots of barley plants.     

Response of the Frog Skin to Steady-State Voltage Clamping : II. The active pathway

Active Na transport across frog skin was separated from passive Na movement utilizing urea influx as a measure of passive (shunt) permeability. In this manner, the response of the overall active Na transport system to an applied potential was determined over a range from +200 mV to -100 mV. Active Na transport displays saturation as a function of applied potential, and both the level of saturation and the potential at which it is achieved are functions of the Na concentration in the external solution. The saturation with potential appears to involve a different step in the transport process than the saturation of Na flux as a function of external Na concentration. The observations can be qualitatively described by either a one-barrier or two-barrier model of the Na transport system.     

Differential responses to ultraviolet irradiation of the polar cytoplasm ofDrosophila eggs: II. Response to dose

Summary The posterior pole cytoplasm of early embryos ofDrosophila melanogaster was irradiated with increasing doses of U.V. light at a wave length specific for nucleic acids 35 and 75 min after ovoposition, when nuclei were still inside the yolk mass. Probit analysis showed that:Sterility was higher in irradiations performed at 35 min.Mortality was higher in the experiment performed at 75 min.After treatment at 35 min, sterility and mortality were independent phenomena.The numbers of targets involved in germ cell determination were of the order of tens and hundreds at 35 and 75 min respectively.The numbers of targets involved in viability were of several orders of magnitude in both developmental stages.The irradiation, even at very low doses, caused a background effect which was probably due to old embryos. The sex ratio was distorted in favour of females at high doses and of males at low doses.     

Short communication. Carbon and nitrogen fluxes in the oceans: the contribution by zooplankton migrants to active transport in the North Atlantic during the Joint Global Ocean Flux Study

The role of vertical migrant zooplankton, with both seasonal/ontogenetic and daily strategies, in the active transport of carbon and nitrogen out of the surface layer in the North Atlantic is analysed. The data used were obtained mainly during the Joint Global Ocean Flux Study (JGOFS)-North Atlantic Bloom Experiment (NABE) (1989-1990) in the North Atlantic and from published information on the biochemical composition of the dominant genera/species. The resulting estimates of active transport are compared with the values of sedimentation rates at the JGOFS-NABE stations and other sites in the North Atlantic. The estimates obtained support previous findings indicating that active transport, especially by interzonal diel migrants, should be taken into account in the estimation of total carbon and nitrogen export flux. The contribution of seasonal migrants to carbon export flux, however, has been considerably underestimated before, although it appears to be significantly lower compared to that of diel migrants. Biomass estimates and biochemical composition, together with mortality and metabolic rates, should be investigated in further detail for some of the dominant species in oceanic areas in order to evaluate active transport more precisely.      

Ribonucleic Acid and Protein Metabolism in Pea Epicotyls : II. Response to Wounding in Aged Tissue

Aged pea Pisum sativum L. var Alaska epicotyl tissue was wounded by excising the apical 10 or 20 millimeters and incubating the excised segments upright in buffer. Wounding induced a very rapid formation of polysomes which was accompanied by minor increases in ribosomes, mRNA, and poly(A) and by a doubling of the in vivo protein synthesizing capacity. This increase in protein synthesis in vivo was matched by a similar increase in polypeptide synthesis in vitro in wheat germ reactions primed by polysomes. However, in vitro reactions primed by total and polysomal RNA from wounded tissue were affected much less.     

Leaf Conductance in Relation to Rate of CO(2) Assimilation: II. Effects of Short-Term Exposures to Different Photon Flux Densities

When photon flux density incident on attached leaves of Zea mays L. was varied from the equivalent of 0.12 of full sunlight to full sunlight, leaf conductance to CO₂ transfer, g, changed in proportion to the change in rate of CO₂, assimilation, A, with the result that intercellular partial pressure of CO₂ remained almost constant. The proportionality was the same as that previously found in g and A measured at one photon flux density in plants of Zea mays L. grown at different levels of mineral nutrition, light intensities, and ambient partial pressures of CO₂. In shade-grown Phaseolus vulgaris L. plants, A as photon flux density was increased from about 0.12 up to about 0.5 full sunlight, the proportionality being almost the same in plants grown at low and at high light intensity.

When photon flux density incident on the adaxial and abaxial surfaces of the isolateral leaves of Eucalyptus pauciflora Sieb. ex Spreng was varied, g and A also varied proportionally. The leaf conductance in a particular surface was affected by the photon flux density at the opposite surface to a greater extent than was expected on the basis of transmittance. The results indicated that stomata may, in some way, be sensitive to the photon flux absorbed within the leaf as a whole.

     

A Semidian Rhythm in the Flowering Response of Pharbitis nil to Far-Red Light: II. The Involvement of Phytochrome

The semidian (~12 h) periodicity in the effect of far-red (FR) interruptions of the light period preceding inductive darkness on flowering in Pharbitis nil appears to be mediated by phytochrome: (a) promotion by interruptions 2 hours before inductive darkness (−2 hours) and inhibition at −8 hours are greater the higher the proportion of FR/R+FR during the interruption; (b) brief FR exposures followed by darkness are even more effective than FR throughout; (c) the effect of brief FR is reversed by subsequent R; (d) R interruptions of an FR background are most promotive at −8 hours, when FR is most inhibitory. Promotive FR interruptions at −2 or −14 hours shorten the critical dark period whereas inhibitory FR interruptions at −8 hours lengthen it. We conclude that the semidian rhythm is controlled by a `timing pool' of phytochrome FR absorbing form (Pfr) which disappears rapidly in darkness: four different estimates from our experiments indicate that Pfr was reduced to the level set by FR within 20 to 45 minutes in darkness. However, flowering may also be influenced by a `metabolic pool' of Pfr with a delayed loss in darkness, the time of which can be advanced or retarded by shifting the semidian rhythm.     

Regulation of Soybean Nitrogen Fixation in Response to Rhizosphere Oxygen: II. Quantification of Nodule Gas Permeability

Nodule nitrogen fixation rates are regulated by a mechanism which is responsive to the rhizosphere oxygen concentration. In some legumes, this oxygen-sensitive mechanism appears to involve changes in the gas permeability of a diffusion barrier in the nodule cortex. In soybean evidence for such a mechanism has not been found. The purpose of this research was to make quantitative measurements of soybean nodule gas permeability to test the hypothesis that soybean nodule gas permeability is under physiological control and responsive to the rhizosphere oxygen concentration. Intact hydroponically grown soybean plants were exposed to altered rhizosphere oxygen concentrations, and the nodule gas permeability, acetylene reduction and nodule respiration rates were repeatedly assayed. After a change in the external oxygen concentration, nitrogenase activity and nodule respiration rates displayed a short-term transient response after which the values returned to rates similar to those observed under ambient oxygen conditions. In contrast to steady-state nitrogenase activity and nodule respiration, nodule gas permeability was dramatically affected by the change in oxygen concentration. Decreasing the external oxygen concentration to 0.1 cubic millimeter per cubic millimeter resulted in a mean increase in nodule gas permeability of 63%. Increasing the rhizosphere oxygen concentration resulted in decreased nodule gas permeability. These data are consistent with the hypothesis that soybean nodules are capable of regulating nitrogen fixation and nodule respiration rates in response to changes in the rhizosphere oxygen concentration and indicate that the regulatory mechanism involves physiological control of the nodule gas permeability.     

Urinary steroid evaluations to monitor ovarian function in exotic ungulates: VII. Urinary progesterone metabolites in the Equidae assessed by immunoassay

A direct enzyme immunoassay (EIA) for non-specific urinary progesterone (Po) metabolites, utilizing a non-specific monoclonal antibody against pregnanediol-3-glucuronide, was evaluated for the purpose of assessing luteal function in equids. Urinary pregnanediol-3-glucuronide (PdG) and immunoreactive PdG-like conjugate (iPdG) concentrations, indexed by creatinine, were compared to plasma Po concentrations in non-conceptive ovarian cycles through two ovulations in four mares. High-performance liquid chromatography (HPLC) of urine from lutealphase mares and a pregnant zebra revealed an absence of significant concentrations of PdG and the presence of at least three immunoreactive compounds, all of which were more polar than PdG. The concentration of iPdG in the mare ranged from a nadir of approximately 3 ng/mg Cr at the time of ovulation to nearly 400 ng/mg Cr at the mid-luteal-phase peak and paralleled plasma Po concentrations. This non-radiometric assay for iPdG permits the assessment of ovulation, luteal formation and function, and luteolysis in unprocessed urine samples from domestic mares. Data from a single zebra indicate this approach also will permit simplified and non-invasive longitudinal studies of ovarian function among a wide range of Equidae.