Branching design of the bronchial tree based on a diameter-flow relationship

Kitaoka, Hiroko, and Béla Suki. Branching designof the bronchial tree based on a diameter-flow relationship.J. Appl. Physiol. 82(3): 968-976, 1997.We propose a method for designing the bronchial tree where thebranching process is stochastic and the diameter(d) of a branch is determined by itsflow rate (Q). We use two principles: the continuumequation for flow division and a power-law relationship betweend and Q, given by Q ~ dⁿ,where n is the diameter exponent. The value ofn has been suggested to be ~3. Weassume that flow is divided iteratively with a random variable for theflow-division ratio, defined as the ratio of flow in the branch to thatin its parent branch. We show that the cumulative probabilitydistribution function of Q, P(>Q) is proportional to Q¹. Weanalyzed prior morphometric airway data (O. G. Raabe, H. C. Yeh, H. M. Schum, and R. F. Phalen, Report No.LF-53, 1976) and found that the cumulative probabilitydistribution function of diameters, P(>d), isproportional to dⁿ, which supportsthe validity of Q ~ dⁿ sinceP(>Q) ~ Q¹. This allowed us toassign diameters to the segments of the flow-branching pattern. Wemodeled the bronchial trees of four mammals and found that theirstatistical features were in good accordance with the morphometricdata. We conclude that our design method is appropriate for robustgeneration of bronchial tree models.

     

Quantification of fungiform papillae and taste pores in living human subjects

A method developed to quantify taste buds in living human subjectsto study the relationship between taste sensitivity and tastebud distribution was used to count the taste buds in 10 humansubjects; fungiform papillae were mapped in 12 subjects. Tastebuds were identified by staining taste pores with methyleneblue, and images of the papillae and their taste pores wereobtained with videomicroscopy and an image processor. Fungiformpapillae showed a 3.3-fold range in density, from 22.1 to 73.6papillae/cm² with an average of 41.1 ± 16.8/cm² (s.d.,n = 2). There was a 14-fold range in taste pore density, from36 to 511 pores/cm² among subjects, with an average of 193 ±133/cm² (s.d., n = 10). Fungiform papillae contained from 0to 22 taste pores, with an average per subject of 3.75 ±1.4 taste pores/papilla (s.d., n = 10). We hypothesize thatsome differences in human taste sensitivity may be related tothese variations in taste bud density.     

Electronic nose for estimation of product concentration in mammalian cell cultivation

The off-gas composition from perfusion cultivation of a CHO-cell line producing recombinant human blood coagulation Factor VIII is monitored with an electronic nose. It is shown that the electronic nose in combination with an artificial neural network can be used for on-line estimation of the Factor VIII concentration in production-scale cultivations. The obtained prediction error (1†) for the Factor VIII concentration was 1.1 IU/ml. The potential of the electronic nose for estimation of viable cell count is outlined in laboratory-scale Factor VIII cultivations. The obtained prediction error (1†) for the viable cell count was 0.4᎒⁶ cells/ml. The results show that this non-invasive method is potentially useful for on-line bioprocess monitoring.     

Control of ascorbic acid efflux in rat luteal cells: role of intracellular calcium and oxygen radicals

In luteal cells, prostaglandin (PG)F_2a mobilizes intracellular calcium concentration ([Ca]_i), generates reactive oxygen species (ROS), depletes ascorbic acid (AA) levels, inhibits steroidogenesis, and ultimately induces cell death. We investigated the hypothesis that [Ca]_i mobilization stimulates ROS, which results in depletion of cellular AA in rat luteal cells. We used a self-referencing AA-selective electrode that noninvasively measures AA flux at the extended boundary layer of single cells and fluorescence microscopy with fura 2 and dichlorofluorescein diacetate (DCF-DA) to measure [Ca]_i and ROS, respectively. Menadione, a generator of intracellular superoxide radical (), PGF_2a, and calcium ionophore were shown to increase [Ca]_i and stimulate intracellular ROS. With calcium ionophore and PGF_2a, but not menadione, the generation of ROS was dependent on extracellular calcium influx. In unstimulated cells there was a net efflux of AA of 121.5 ± 20.3 fmol · cm^–1 · s^–1 (mean ± SE, n = 8), but in the absence of extracellular calcium the efflux was significantly reduced (10.3 ± 4.9 fmol · cm^–1 · s^–1; n = 5, P < 0.05). PGF_2a and menadione stimulated AA efflux, but calcium ionophore had no significant effect. These data suggest two AA regulatory mechanisms: Under basal conditions, AA efflux is calcium dependent and may represent recycling and maintenance of an antioxidant AA gradient at the plasma membrane. Under luteolytic hormone and/or oxidative stress, AA efflux is stimulated that is independent of extracellular calcium influx or generation of ROS. Although site-specific mobilization of calcium pools and ROS cannot be ruled out, the release of AA by PGF_2a-stimulated luteal cells may occur through other signaling pathways. luteolysis; apoptosis; self-referencing microelectrode     

{micro}-Calpain and calpain-3 are not autolyzed with exhaustive exercise in humans

µ-calpain and calpain-3 are Ca²⁺-dependent proteases found in skeletal muscle. Autolysis of calpains is observed using Western blot analysis as the cleaving of the full-length proteins to shorter products. Biochemical assays suggest that µ-calpain becomes proteolytically active in the presence of 2–200 µM Ca²⁺. Although calpain-3 is poorly understood, autolysis is thought to result in its activation, which is widely thought to occur at lower intracellular Ca²⁺ concentration levels ([Ca²⁺]_i; 1 µM) than the levels at which µ-calpain activation occurs. We have demonstrated the Ca²⁺-dependent autolysis of the calpains in human muscle samples and rat extensor digitorum longus (EDL) muscles homogenized in solutions mimicking the intracellular environment at various [Ca²⁺] levels (0, 2.5, 10, and 25 µM). Autolysis of calpain-3 was found to occur across a [Ca²⁺] range similar to that for µ-calpain, and both calpains displayed a seemingly higher Ca²⁺ sensitivity in human than in rat muscle homogenates, with 15% autolysis observed after 1-min exposure to 2.5 µM Ca²⁺ in human muscle and almost none after 1- to 2-min exposure to the same [Ca²⁺]_i level in rat muscle. During muscle activity, [Ca²⁺]_i may transiently peak in the range found to autolyze µ-calpain and calpain-3, so we examined the effect of two types of exhaustive cycling exercise (30-s "all-out" cycling, n = 8; and 70% O_{2 peak} until fatigue, n = 3) on the amount of autolyzed µ-calpain or calpain-3 in human muscle. No significant autolysis of µ-calpain or calpain-3 occurred as a result of the exercise. These findings have shown that the time- and concentration-dependent changes in [Ca²⁺]_i that occurred during concentric exercise fall near but below the level necessary to cause autolysis of calpains in vivo. Ca²⁺-dependent proteases; proteolysis     

Auxin Transport in Secondary Tissues1

Auxin transport was investigated in excised stem segments ofNicotiana tabacum L. by the agar block technique using [1-¹⁴C]indol-3yl-acetic acid (IAA). The ability of the stems to transportauxin basipetally increased as secondary development proceeded;by contrast the ability of the pith to transport auxin declinedwith age. By separation of the stem tissues it was shown thatthe great majority of auxin transport took place in cells associatedwith the internal phloem and in cells close to the cambium;in both cases similar velocities of transport were found (c.5.0 mm h^–1 at 22°C). The effects of osmotic gradientson auxin transport through the internal phloem were investigated.IAA was found by chromatography to account for practically allthe radioactivity in receiver blocks and other extracts of stemsegments. The significance of these results is discussed.     

SGK1 activates Na+-K+-ATPase in amphibian renal epithelial cells

Serum- and glucocorticoid-induced kinase 1 (SGK1) is thought to be an important regulator of Na⁺ reabsorption in the kidney. It has been proposed that SGK1 mediates the effects of aldosterone on transepithelial Na⁺ transport. Previous studies have shown that SGK1 increases Na⁺ transport and epithelial Na⁺ channel (ENaC) activity in the apical membrane of renal epithelial cells. SGK1 has also been implicated in the modulation of Na⁺-K⁺-ATPase activity, the transporter responsible for basolateral Na⁺ efflux, although this observation has not been confirmed in renal epithelial cells. We examined Na⁺-K⁺-ATPase function in an A6 renal epithelial cell line that expresses SGK1 under the control of a tetracycline-inducible promoter. The results showed that expression of a constitutively active mutant of SGK1 (SGK1^T_S425D) increased the transport activity of Na⁺-K⁺-ATPase 2.5-fold. The increase in activity was a direct consequence of activation of the pump itself. The onset of Na⁺-K⁺-ATPase activation was observed between 6 and 24 h after induction of SGK1 expression, a delay that is significantly longer than that required for activation of ENaC in the same cell line (1 h). SGK1 and aldosterone stimulated the Na⁺ pump synergistically, indicating that the pathways mediated by these molecules operate independently. This observation was confirmed by demonstrating that aldosterone, but not SGK1^T_S425D, induced an 2.5-fold increase in total protein and plasma membrane Na⁺-K⁺-ATPase ₁-subunit abundance. We conclude that aldosterone increases the abundance of Na⁺-K⁺-ATPase, whereas SGK1 may activate existing pumps in the membrane in response to chronic or slowly acting stimuli. sodium transport; serum- and glucocorticoid-induced kinase; A6 cells; sodium pump     

The Transport and Metabolism of Urea in Chara australis: II. UREASE AND THE DISTRIBUTION OF TRANSPORTED UREA

The ureolytic enzyme in Chara was investigated. This enzymewas shown to be a urease with an unusually high affinity forurea(K_m = 158 mmol m^-3). Little inhibition of urease activitywas found when intact Chara cells were exposed to the ureaseinhibitors hydroxyurea, acetohydroxamic acid and N-ethylmaleimide,although there was some inhibition of urea uptake. The distribution of radioactivity amongst the amino acid, organicacid and sugar/neutral fractions, determined by ion-exchangechromatography, was very similar whether the Chara internodeswere exposed to ¹⁴C-urea or to H¹⁴CO₃. This suggests that thefraction of the urea-carbon liberated by the urease as CO₂ andretained by the cell is used in photosynthetic carbon-fixation.During the initial 15 min of ¹⁴C-urea uptake, label appearsin the vacuole only in the form of unmetabolized urea. Afterthis time a variety of labelled compounds appear in the vacuole,presumably reflecting the gradual movement of carbon-fixationproducts from the chloroplasts to the cytoplasm and thence intothe vacuole. Key words: Urea transport, metabolism, Chara, urease     

New insights into the molecular and cellular workings of the cardiac Na+/Ca2+ exchanger

The cardiac Na⁺/Ca²⁺ exchanger (NCX1) is almost certainly the major Ca²⁺ extrusion mechanism in cardiac myocytes, although the driving force for Ca²⁺ extrusion is quite small. To explain multiple recent results, it is useful to think of the exchanger as a slow Ca²⁺ buffer that can reverse its function multiple times during the excitation-contraction cycle (ECC). An article by the group of John Reeves brings new insights to this function by analyzing the role of regulatory domains of NCX1 that mediate its activation by a rise of cytoplasmic Ca²⁺. It was demonstrated that the gating reactions are operative just in the physiological range of Ca²⁺ changes, a few fold above resting Ca²⁺ level, and that they prevent the exchanger from damping out the influence of mechanisms that transiently increase Ca²⁺ levels. Furthermore, exchangers with deleted regulatory domains are shown to reduce resting Ca²⁺ to lower levels than achieved by wild-type exchangers. A study by the group of Kenneth Philipson demonstrated that the NCX1 regulatory domain can bind and respond to Ca²⁺ changes on the time scale of the ECC in rat myocytes. At the same time, studies of transgenic mice and NCX1 knockout mice generated by the Philipson group revealed that large changes of NCX1 activity have rather modest effects on ECC. Simple simulations predict these results very well: murine cardiac ECC is very sensitive to small changes of the Na⁺ gradient, very sensitive to changes of the sarcoplasmic reticulum Ca²⁺ pump activity, and very insensitive to changes of NCX1 activity. It is speculated that the NCX1 gating reactions not only regulate coupled 3Na⁺:1Ca²⁺ exchange but also control the exchanger’s Na⁺ leak function that generates background Na⁺ influx and depolarizing current in cardiac myocytes. excitation-contraction cycle     

Pharmacological and biophysical isolation of K+ currents encoded by ether-à-go-go-related genes in murine hepatic portal vein smooth muscle cells

The functional properties of the Saccharomyces cerevisiae bicarbonate transporter homolog Bor1p (YNL275wp) were characterized by measuring boron (H₃BO₃), Na⁺, and Cl^– fluxes. Neither Na⁺ nor Cl^– appears to be a transported substrate for Bor1p. Uphill efflux of boron mediated by Bor1p was demonstrated directly by loading cells with boron and resuspending in a low-boron medium. Cells with intact BOR1, but not the deletant strain, transport boron outward until the intracellular concentration is sevenfold lower than that in the medium. Boron efflux through Bor1p is a saturable function of intracellular boron (apparent K_m 1–2 mM). The extracellular pH dependences of boron distribution and efflux indicate that uphill efflux is driven by the inward H⁺ gradient. Addition of 30 mM HCO₃^– does not affect boron extrusion by Bor1p, indicating that HCO₃^– does not participate in Bor1p function. Functional Bor1p is present in cells grown in medium with no added boron, and overnight growth in 10 mM H₃BO₃ causes only a small increase in the levels of functional Bor1p and in BOR1 mRNA. The fact that Bor1p is expressed when there is no need for boron extrusion and is not strongly induced in the presence of growth-inhibitory boron concentrations is surprising if the main physiological function of yeast Bor1p is boron efflux. A possible role in vacuolar dynamics for Bor1p was recently reported by Decker and Wickner (10). Under the conditions used presently, there appears to be mildly abnormal vacuolar morphology in the deletant strain. boron; SLC4; YNL275w     

Role of aspartate residues in Ca(2+) affinity and permeation of the distal ECaC1

The Ca²⁺ affinity andpermeation of the epithelial Ca²⁺ channel (ECaC1) wereinvestigated after expression in Xenopus oocytes. ECaC1displayed anomalous mole-fraction effects. Extracellular Ca²⁺ and Mg²⁺ reversibly inhibited ECaC1 wholecell Li⁺ currents: IC₅₀ = 2.2 ± 0.4 µM (n = 9) and 235 ± 35 µM (n = 10), respectively. These values compare well with theCa²⁺ affinity of the L-type voltage-gated Ca²⁺(Ca_V1.2) channel measured under the same conditions,suggesting that high-affinity Ca²⁺ binding is awell-conserved feature of epithelial and voltage-gated Ca²⁺channels. Neutralization of D550 and E535 in the pore region had nosignificant effect on Ca²⁺ and Mg²⁺ affinities.In contrast, neutralization of D542 significantly decreasedCa²⁺ affinity (IC₅₀ = 1.1 ± 0.2 mM,n = 6) and Mg²⁺ affinity(IC₅₀ > 25 ± 3 mM, n = 4).Despite a 1,000-fold decrease in Ca²⁺ affinity in D542N,Ca²⁺ permeation properties and theCa²⁺-to-Ba²⁺ conductance ratio remainedcomparable to values for wild-type ECaC1. Together, our observationssuggest that D542 plays a critical role in Ca²⁺ affinitybut not in Ca²⁺ permeation in ECaC1.

     

Acoustics and freshwater zooplankton

We investigated the potential of acoustic technology for estimatingzooplankton distribution as part of an ongoing study of sockeyesalmon (Oncorhynchus nerka) production in three lakes of theFraser River system, British Columbia. Simultaneous acousticand zooplankton samples were obtained in 1 and 2 m depth incrementsfrom the surface to 30 m at mid-lake stations. We derived asignificant regression relationship (r²=0.71, n=79) betweenzooplankton biomass ranging between 5 and 220 mg m^–3 andacoustic backscatter (V²). The ensuing regression model wasused to predict zooplankton biomass distribution from acousticdata collected along transects representing different lake areas.     

Effect of IBMX and alkaline phosphatase inhibitors on Cl- secretion in G551D cystic fibrosis mutant mice

Some cysticfibrosis transmembrane conductance regulator (CFTR) mutations, such asG551D, result in a correctly localized Cl channel at the cellapical membrane, albeit with markedly reduced function. Patch-clampstudies have indicated that both phosphatase inhibitors and3-isobutyl-1-methylxanthine (IBMX) can induceCl secretion through theG551D mutant protein. We have now assessed whether these agents caninduce Cl secretion incftr^G551D mutantmice. No induction of Clsecretion was seen with the alkaline phosphatase inhibitorsbromotetramisole or levamisole in either the respiratory or intestinaltracts of wild-type orcftr^G551D mice.In contrast, in G551D intestinal tissues, IBMX was able to produce asmall CFTR-related secretory response [means ± SE: jejunum,1.8 ± 0.9 µA/cm²,n = 7; cecum, 3.7 ± 0.8 µA/cm²,n = 7; rectum (in vivo),1.9 ± 0.9 mV, n = 5]. Thiswas approximately one order of magnitude less than the wild-typeresponse to this agent and, in the cecum, was significantly greaterthan that seen in null mice(cftr^UNC). Inthe trachea, IBMX produced a transientCl secretory response (37.3 ± 14.7 µA/cm²,n = 6) of a magnitude similar to thatseen in wild-type mice (33.7 ± 4.7 µA/cm²,n = 9). This response was also presentin null mice and therefore is likely to be independent of CFTR. Noeffect of IBMX on Clsecretion was seen in the nasal epithelium ofcftr^G551D mice.We conclude that IBMX is able to induce detectable levels ofCFTR-related Cl secretionin the intestinal tract but not the respiratory tract through the G551Dmutant protein.

     

Caco-2 intestinal cell differentiation is associated with G1 arrest and suppression of CDK2 and CDK4

The cellular mechanisms regulating intestinal proliferation anddifferentiation remain largely undefined. Previously, we showed anearly induction of the cyclin-dependent kinase (CDK) inhibitor p21^Waf1/Cip1 in Caco-2 cells, ahuman colon cancer line that spontaneously differentiates into a smallbowel phenotype. The purpose of our present study was to assess thetiming of cell cycle arrest in relation to differentiation in Caco-2cells and to examine the mechanisms responsible for CDK inactivation.Caco-2 cells undergo a relativeG₁/S block and cease toproliferate at day3 postconfluency; an increase in theactivity of terminally differentiated brush-border enzymes (sucrase andalkaline phosphatase) was noted at day6 postconfluency. Cell cycle block wasassociated with suppression of both CDK2 and CDK4 activities, which areimportant for G₁/S progression.Treatment of the CDK immune complexes with the detergent deoxycholate(DOC) resulted in restoration of CDK2, but not CDK4, activity atday 3 postconfluency, suggesting the presence of inhibitory protein(s)binding to the cyclin/CDK2 complex at this time point. An increasedbinding of p21^Waf1/Cip1 to CDK2complexes at day3 postconfluency was noted, suggesting a potential role for p21^Waf1/Cip1in CDK2 inactivation; however, immunodepletion ofp21^Waf1/Cip1 from Caco-2 proteinextracts demonstrated thatp21^Waf1/Cip1 is only partiallyresponsible for CDK2 suppression atday 3 postconfluency. A decrease in the cyclin E/CDK2 complex appears tocontribute to the CDK2 inactivation noted atdays6 and12 postconfluency. Taken together, ourresults suggest that multiple mechanisms contribute to CDK suppressionduring Caco-2 cell differentiation. Inhibition of CDK2 and CDK4 leadsto G₁ arrest and inhibition ofproliferation that precede Caco-2 cell differentiation.

     

Diaphragm disuse reduces Ca2+ uptake capacity of sarcoplasmic reticulum

Howell, Sandra, Wen-Zhi Zhan, and Gary C. Sieck.Diaphragm disuse reduces Ca²⁺uptake capacity of sarcoplasmic reticulum. J. Appl.Physiol. 82(1): 164-171, 1997.Chronic phrenictetrodotoxin (TTX) blockade and phrenic denervation (Dnv) of hamsterdiaphragm result in decreased maximum specific tension, prolongedcontraction time, and improved fatigue resistance (W. Z. Zhan and G. C. Sieck. J. Appl. Physiol. 72:1445-1453, 1992). An underlying increased relative contribution oftype I fibers to total muscle mass appears to be consistent with, butdoes not completely account for, changes in contractile and fatigueproperties. The present study was designed to evaluate a potential rolefor altered cellular Ca²⁺metabolism in the adaptive response of the diaphragm to chronic disuse.An analytic method based on simulation and modeling of long-term⁴⁵Ca²⁺efflux data was used to estimateCa²⁺ contents (nmolCa²⁺/g wet wt tissue) and exchangefluxes (nmolCa^{2+ ·} min^{1 ·} g¹)for extracellular and intracellular compartments in the in vitro hamster hemidiaphragm after prolonged disuse. Three groups were compared: control (Con, n = 5),phrenic TTX blockade (TTX, n = 5), andphrenic denervation (Dnv, n = 5).Experimental muscles were loaded with⁴⁵Ca²⁺for 1 h, and efflux data were collected for 8 h by using a flow-through tissue chamber. Compartmental analysis of efflux data estimated thatthe Ca²⁺ contents andCa²⁺ exchange fluxes of thelargest and slowest intracellular compartment (putative longitudinalreticulum) were reduced by ~50% in TTX and Dnv muscle groupscompared with Con. In addition, the kinetic model predicted significantdecreases in total intracellularCa²⁺ and total diaphragmCa²⁺ in TTX and Dnv muscles. Weconclude that the data support the hypothesis that the capac- ity ofthe sarcoplasmic reticulum for Ca²⁺ sequestration is reduced inchronic diaphragm disuse. The impact of this effect on diaphragmcontractile and fatigue properties is discussed.

     

Anchoring protein is required for cAMP-dependent stimulation of L-type Ca2+ channels in rabbit portal vein

Stimulation of cardiac L-typeCa²⁺ channels by cAMP-dependentprotein kinase (PKA) requires anchoring of PKA to a specificsubcellular environment by A-kinase anchoring proteins (AKAP). Thisstudy evaluated the possible requirement of AKAP in PKA-dependentregulation of L-type Ca²⁺ channelsin vascular smooth muscle cells using the conventional whole cellpatch-clamp technique. Peak Ba²⁺current in freshly isolated rabbit portal vein myocytes wassignificantly increased by superfusion with either 0.5 µM isoproterenol (131 ± 3% of the control value,n = 11) or 10 µM 8-bromoadenosine3',5'-cyclic monophosphate (8-BrcAMP; 114 ± 1%,n = 8). The PKA-induced stimulatory effects ofboth isoproterenol and 8-BrcAMP were completely abolished by a specificPKA inhibitor KT-5720 (0.2 µM) or by dialyzing cells with Ht 31 (100 µM), a peptide that inhibits the binding of PKA to AKAP. In contrast,Ht 31 did not block the excitatory effect of the catalytic subunit ofPKA when dialyzed into the cells. These data suggest that stimulationof Ca²⁺ channels in vascularmyocytes by endogenous PKA requires localization of PKA through bindingto AKAP.

     

The mitochondrial external NADPH dehydrogenase modulates the leaf NADPH/NADP+ ratio in transgenic Nicotiana sylvestris

Plant mitochondria contain alternative external NAD(P)H dehydrogenases,which oxidize cytosolic NADH or NADPH and reduce ubiquinonewithout inherent linkage to proton pumping and ATP production.In potato, St-NDB1 is an external Ca²⁺-dependent NADPH dehydrogenase.The physiological function of this enzyme was investigated inhomozygous Nicotiana sylvestris lines overexpressing St-ndb1and co-suppressing St-ndb1 and an N. sylvestris ndb1. In leafmitochondria isolated from the overexpressor lines, higher activityof alternative oxidase (AOX) was detected. However, the AOXinduction was substantially weaker than in the complex I-deficientCMSII mutant, previously shown to contain elevated amounts ofNAD(P)H dehydrogenases and AOX. An aox1b and an aox2 gene wereup-regulated in CMSII, but only aox1b showed a response, albeitsmaller, in the transgenic lines, indicating differences inAOX activation between the genotypes. As in CMSII, the increaseof AOX in the overexpressing lines was not due to a generaloxidative stress. The lines overexpressing St-ndb1 had consistentlylowered leaf NADPH/NADP⁺ ratios in the light and variably decreasedlevels in darkness, but unchanged NADH/NAD⁺ ratios. CMSII insteadhad similar NADPH/NADP⁺ and lower NADH/NAD⁺ ratios than thewild type. These results demonstrate that St-NDB1 is able tomodulate the cellular balance of NADPH and NADP⁺ at least inthe day and that reduction of NADP(H) and NAD(H) is independentlycontrolled. Similar growth rates, chloroplast malate dehydrogenaseactivation and xanthophyll ratios indicate that the change inreduction does not communicate to the chloroplast, and thatthe cell tolerates significant changes in NADP(H) reductionwithout deleterious effects.     

Physiological basis of spacing effects on tree growth and form in Eucalyptus globulus

We examine the effects of spacing and layout on the growth and form of 3- to 4-year-old Eucalyptus globulus in a farm forestry context. Four planting layouts were chosen. These represented the range commonly in use in farm forestry: block plantings (2Ǹ m), triple rows (2Ǹ m) at 10-m intervals, single rows (2᎒ m) and isolated trees (10᎒ m). The physiological significance of key results is interpreted in terms of changes in the parameters of a simple plantation growth model. Under conditions where levels of direct light are high, for example during summer, block-planted trees intercepted only 38% of the light intercepted by isolated trees. On a stand basis, however, the combination of incident radiation and ground coverage declined with lower stand densities. While stand leaf area index declined from around 6 to 1 with increased spacing, individual tree leaf areas rose from around 50 m² in block plantings to 150 m² in isolated trees. The proportion of above-ground biomass found in stems declined with increasing spacing as the mass in foliage and branches increased. Stems accounted for 65% of above-ground biomass in block-planted trees but only 35% in isolated trees. The contributions of leaves and branches correspondingly rose from 19% to 35% and from 16% to 29%, respectively. Changes in biomass distribution were accompanied by increasing branch number, branch thickness, flatter branch angles and the longer retention of lower branches with greater spacing. These changes have implications for the merchantability of the timber. The efficiency of above-ground radiation conversion was constant at 0.67 g MJ^-1 irrespective of spacing. We estimated that foliar maintenance respiration (R_m) accounted for about 90% of above-ground R_m. On a stand basis R_m costs block plantings 23.90 t DM ha^-1 year^-1 (50% annual above-ground photosynthetic production) compared with 6.22 t DM ha^-1 year^-1 (40% annual above-ground photosynthetic production) in stands of isolated trees.     

Mechanisms of stimulation of vagal pulmonary C fibers by pulmonary air embolism in dogs

Chen, H. F., B. P. Lee, and Y. R. Kou. Mechanisms ofstimulation of vagal pulmonary C fibers by pulmonary air embolism indogs. J. Appl. Physiol. 82(3):765-771, 1997.We investigated the involvement of thecyclooxygenase metabolites and hydroxyl radical (^· OH) in thestimulation of vagal pulmonary C fibers (PCs) by pulmonary air embolism(PAE). Impulses were recorded from PCs in 51 anesthetized, open-chest,and artificially ventilated dogs. Fifty of 59 PCs were stimulated byinfusion of air into the right atrium (0.2 ml ^· kg^{1 ·} min¹for 10 min). As a group (n = 59), PCactivity increased from a baseline of 0.4 ± 0.1 to a peak of 1.7 ± 0.2 impulses/s during the period from 1 min before to 2 min afterthe termination of PAE induction. In PCs initially stimulated by PAEinduction, PAE was repeated after the intervening treatment (iv) withsaline (n = 9), ibuprofen (acyclooxygenase inhibitor; n = 11), ordimethylthiourea (a ^· OH scavenger;n = 12). The responses of PCs to PAEwere not altered by saline vehicle but were abolished by ibuprofen and significantly attenuated by dimethylthiourea. Although hyperinflation of the lungs reversed the PAE-induced bronchomotor responses, it didnot reverse the stimulation of PCs (n = 8). These results suggest that 1)cyclooxygenase products are necessary for the stimulation of PCs byPAE, whereas changes in lung mechanics are not, and2) the functional importance ofcyclooxygenase products may be mediated in part through the formationof ^· OH.

     

CFTR upregulates the expression of the basolateral Na+-K+-2Cl- cotransporter in cultured pancreatic duct cells

The purpose ofthe current experiments was 1) toassess basolateralNa⁺-K⁺-2Clcotransporter (NKCC1) expression and2) to ascertain the role of cysticfibrosis transmembrane conductance regulator (CFTR) in the regulationof this transporter in a prototypical pancreatic duct epithelial cellline. Previously validated human pancreatic duct celllines (CFPAC-1), which exhibit physiological features prototypical ofcystic fibrosis, and normal pancreatic duct epithelia (stablerecombinant CFTR-bearing CFPAC-1 cells, termed CFPAC-WT) were grown toconfluence before molecular and functional studies. High-stringencyNorthern blot hybridization, utilizing specific cDNA probes, confirmedthat NKCC1 was expressed in both cell lines and its mRNA levels weretwofold higher in CFPAC-WT cells than in CFPAC-1 cells(P < 0.01, n = 3).Na⁺-K⁺-2Clcotransporter activity, assayed as the bumetanide-sensitive, Na⁺- andCl-dependentNH⁺₄ entry into the cell (withNH⁺₄ acting as a substitute forK⁺), increased by ~115% inCFPAC-WT cells compared with CFPAC-1 cells(P < 0.01, n = 6). Reducing the intracellularCl by incubating the cellsin a Cl-free mediumincreasedNa⁺-K⁺-2Clcotransporter activity by twofold (P < 0.01, n = 4) only in CFPAC-WT cells. We concluded that NKCC1 is expressed in pancreatic duct cellsand mediates the entry ofCl. NKCC1 activity isenhanced in the presence of an inwardCl gradient. The resultsfurther indicate that the presence of functional CFTR enhances theexpression of NKCC1. We speculate that CFTR regulates this process in aCl-dependent manner.