An empirical model of primary productivity (14C) using mesocosm data along a nutrient gradient

The two parameters of the hyperbolic tangent equation, P_m and, were estimated from in situ vertical profiles of primary productionusing mesocosm data along a nutrient gradient. The parameters,derived from 4-h (around noon) ¹⁴C incubations, were used togetherwith the photosynthesis-light curve and hourly solar radiationdata to calculate daily primary production rates (P_d). Approximately40% of the daily production occurred in the 4 h around noon.Considering parameter uncertainty, there was no indication ofan increase in variation in production with increased nutrientloading, nor did biomass-specific P-I parameters increase. Annualproduction ranged from 82 to 901 g C m^–2 year^–1and was highest in the highest nutrient treatment tank. Dailyproductivity ranged from 0.02 to 9.1 g C m^–2 day^–1and was significantly correlated, in all treatments, with acomposite parameter BI₀/k (where B is phytoplankton biomass;I₀ is daily radiation and k is the extinction coefficient).Linear regressions of P_d against BI₀/k indicated that much ofthe variability (86%) in productivity was explained by lightavailability and phytoplankton biomass. Two approaches for predictingproductivity were compared: (i) predicting production directlyfrom environmental variables (i.e. BI₀/k) and (ii) predictingthe parameters of the P-I curve from environmental variablesand using these to calculate daily production.     

Estimation of the photosynthesis/irradiance (P/I) curve parameters from light and dark bottle experiments

Light and dark bottle experiments, carried out in three systemsin the Netherlands, were used to estimate the parameters ofmodels relating the oxygen production rate to incident lightintensity. The maximum production rate (P_M) and the light saturationconstant (I_S) were estimated using both gross and nett oxygenproduction data. In the latter case, the community oxygen consumptionrate (R_ox was also estimated. Eight models were compared withrespect to goodness of fit, as has been accomplished previouslyby Jassby and Platt (Limnol. Oceanogr., 21, 540–547, 1976)and many others. This study, however, emphasizes the problemof parameter correlation and the consequential usefulness ofthese type of experiments to identify the P/I curve parameters.The results show that at a 90% level of confidence, the modelscannot be distinguished with respect to goodness of fit. However,the models do show distinct differences in parameter correlation.Parameter correlation was shown to be related to the shape ofthe curve. P/I curves with high convexity were shown to be lesssensitive for parameter correlation. In particular, models showinglow convexity suffer from over-paraineterisation, which meansthat on the basis of the observed production rates it is difficultto discriminate between the parameters. Also, alternative modelformulations, using P_M and the initial slope (), were investigated.These formulations produced less parameter correlation. However,for models with low convexity, showing high parameter correlationanyway, the reduction is limited. The use of nett oxygen productiondata does not show a significant difference in fit at a 90%confidence level. However, measured R_ox from dark bottle experimentstends to be higher than the values found by estimating R_ox fromnett oxygen production.     

Functional analysis of the R1086H malignant hyperthermia mutation in the DHPR reveals an unexpected influence of the III-IV loop on skeletal muscle EC coupling

Malignant hyperthermia (MH) is an inherited pharmacogenetic disorder caused by mutations in the skeletal muscle ryanodine receptor (RyR1) and the dihydropyridine receptor (DHPR) _1S-subunit. We characterized the effects of an MH mutation in the DHPR cytoplasmic III-IV loop of _1S (R1086H) on DHPR-RyR1 coupling after reconstitution in dysgenic (_1S null) myotubes. Compared with wild-type _1S, caffeine-activated Ca²⁺ release occurred at approximately fivefold lower concentrations in nonexpressing and R1086H-expressing myotubes. Although maximal voltage-gated Ca²⁺ release was similar in _1S- and R1086H-expressing myotubes, the voltage dependence of Ca²⁺ release was shifted 5 mV to more negative potentials in R1086H-expressing myotubes. Our results demonstrate that _1S functions as a negative allosteric modulator of release channel activation by caffeine/voltage and that the R1086H MH mutation in the intracellular III-IV linker disrupts this negative regulatory influence. Moreover, a low caffeine concentration (2 mM) caused a similar shift in voltage dependence of Ca²⁺ release in _1S- and R1086H-expressing myotubes. Compared with _1S-expressing myotubes, maximal L channel conductance (G_max) was reduced in R1086H-expressing myotubes (_1S 130 ± 10.2, R1086H 88 ± 6.8 nS/nF; P < 0.05). The decrease in G_max did not result from a change in retrograde coupling with RyR1 as maximal conductance-charge movement ratio (G_max/Q_max) was similar in _1S- and R1086H-expressing myotubes and a similar decrease in G_max was observed for an analogous mutation engineered into the cardiac L channel (R1217H). In addition, both R1086H and R1217H DHPRs targeted normally and colocalized with RyR1 in sarcoplasmic reticulum (SR)-sarcolemmal junctions. These results indicate that the R1086H MH mutation in _1S enhances RyR1 sensitivity to activation by both endogenous (voltage sensor) and exogenous (caffeine) activators. excitation-contraction coupling; calcium channel; muscle disease     

Potassium Transport Across the Membranes of Chara: III. EFFECTS OF pH, INHIBITORS AND ILLUMINATION

Smith, J. R., Walker, N. A. and Smith, F. A. 1987. Potassiumtransport across the membranes of Chara. III. Effects of pH,inhibitors and illumination.—J. exp. Bot. 38: 778–787. The effects of several treatments, normally used to inhibitelectrogenic proton transport, upon the potassium permeability(P_k) of the membranes of Chara were examined by means of simultaneousmeasurements of the ⁴²K influx (ⁱⁿ_K) and the membrane electricalconductance (G_m). ⁱⁿ_K, P_K and G_mwere found to be substantiallyunaffected when the external pH (pH?) was varied over the range5?0 to 85. However, when pH? was increased to 11 it was foundthat, although G_m increased considerably, both P_k and ⁱⁿ_K decreasedtypically by an order of magnitude. When cells were placed intotal darkness, P_K decreased substantially only after one dayhad elapsed. For the particular experimental conditions used,the inhibitors DES, NaN₃, and La₃₊ were found to alter P_K, whereasDCCD left P_K substantially unaffected. These results suggestthat care must be taken with some common procedures used toexamine the electrical properties of the electrogenic protonpump. Key words: Potassium, pH, illumination, inhibitors     

cAMP-independent phosphorylation activation of CFTR by G proteins in native human sweat duct

It is generally believed thatcAMP-dependent phosphorylation is the principle mechanism foractivating cystic fibrosis transmembrane conductance regulator (CFTR)Cl channels. However, we showed that activating Gproteins in the sweat duct stimulated CFTR Cl conductance(G_Cl) in the presence of ATP alone without cAMP. The objective of this study was to test whether the G protein stimulation of CFTR G_Cl is independent ofprotein kinase A. We activated G proteins and monitored CFTRG_Cl in basolaterally permeabilized sweat duct.Activating G proteins with guanosine5'-O-(3-thiotriphosphate) (10-100 µM) stimulated CFTRG_Cl in the presence of 5 mM ATP alone withoutcAMP. G protein activation of CFTR G_Cl requiredMg²⁺ and ATP hydrolysis (5'-adenylylimidodiphosphate couldnot substitute for ATP). G protein activation of CFTRG_Cl was 1) sensitive to inhibition bythe kinase inhibitor staurosporine (1 µM), indicating that theactivation process requires phosphorylation; 2) insensitive to the adenylate cyclase (AC) inhibitors 2',5'-dideoxyadenosine (1 mM)and SQ-22536 (100 µM); and 3) independent ofCa²⁺, suggesting that Ca²⁺-dependent proteinkinase C and Ca²⁺/calmodulin-dependent kinase(s) are notinvolved in the activation process. Activating AC with10⁶ M forskolin plus 10⁶ M IBMX (in thepresence of 5 mM ATP) did not activate CFTR, indicating that cAMPcannot accumulate sufficiently to activate CFTR in permeabilized cells.We concluded that heterotrimeric G proteins activate CFTR G_Cl endogenously via a cAMP-independent pathwayin this native absorptive epithelium.

     

Interaction of leg stiffness and surface stiffness during human hopping

Ferris, Daniel P., and Claire T. Farley. Interaction ofleg stiffness and surface stiffness during human hopping.J. Appl.Physiol. 82(1): 15-22, 1997.When mammals run,the overall musculoskeletal system behaves as a single linear "legspring." We used force platform and kinematic measurements todetermine whether leg spring stiffness(k_leg) isadjusted to accommodate changes in surface stiffness(k_surf) whenhumans hop in place, a good experimental model for examiningadjustments tok_leg in bouncinggaits. We found thatk_leg was greatlyincreased to accommodate surfaces of lower stiffnesses. The seriescombination ofk_leg andk_surf[total stiffness(k_tot)]was independent ofk_surf at a givenhopping frequency. For example, when humans hopped at a frequency of 2 Hz, they tripled theirk_leg on the leaststiff surface(k_surf = 26.1 kN/m; k_leg = 53.3 kN/m) compared with the most stiff surface(k_surf = 35,000 kN/m; k_leg = 17.8 kN/m). Values fork_tot were notsignificantly different on the least stiff surface (16.7 kN/m) and themost stiff surface (17.8 kN/m). Because of thek_leg adjustment,many aspects of the hopping mechanics (e.g., ground-contact time andcenter of mass vertical displacement) remained remarkably similardespite a >1,000-fold change ink_surf. This studyprovides insight into howk_leg adjustmentscan allow similar locomotion mechanics on the variety of terrainsencountered by runners in the natural world.

     

Recovery of free ADP, Pi, and free energy of ATP hydrolysis in human skeletal muscle

We measuredsignificant undershoots of the concentrations of free ADP([ADP]) and P_i([P_i]) and the freeenergy of ATP hydrolysis (G_ATP) belowinitial resting levels during recovery from severe ischemic exercisewith ³¹P-nuclear magneticresonance spectroscopy in 11 healthy sports students. Undershoots ofthe rate of oxidative phosphorylation would be predicted if the rate ofoxidative phosphorylation would depend solely on free[ADP],[P_i], orG_ATP. However,undershoots of the rate of oxidative phosphorylation have not beenreported in the literature. Furthermore, undershoots of the rate ofoxidative phosphorylation are unlikely because there is evidence that a balance between ATP production and consumption cannot be achieved if anundershoot of the rate of oxidative phosphorylation actually occurs.Therefore, oxidative phosphorylation seems to depend not only on free[ADP],[P_i], orG_ATP. Anexplanation is that acidosis-related or other factors control oxidativephosphorylation additionally, at least under some conditions.

     

Lipopolysaccharide- and gram-positive bacteria-induced cellular inflammatory responses: role of heterotrimeric Galpha(i) proteins

Heterotrimeric G_i proteins may play a role in lipopolysaccharide (LPS)-activated signaling through Toll-like receptor 4 (TLR4), leading to inflammatory mediator production. Although LPS is a TLR4 ligand, the gram-positive bacterium Staphylococcus aureus (SA) is a TLR2 ligand, and group B streptococci (GBS) are neither TLR2 nor TLR4 ligands but are MyD88 dependent. We hypothesized that genetic deletion of G_i proteins would alter mediator production induced by LPS and gram-positive bacterial stimulation. We examined genetic deletion of G_i2 or G_i1/3 protein in G_i2-knockout (G_i2–/–) or G_i1/3-knockout (G_i1/3–/–) mice. LPS-, heat-killed SA-, or GBS-induced mediator production in splenocytes or peritoneal macrophages (M) was investigated. There were significant increases in LPS-, SA-, and GBS-induced production of TNF- and IFN- in splenocytes from G_i2–/– mice compared with wild-type (WT) mice. Also, LPS-induced TNF- was increased in splenocytes from G_i1/3–/– mice. In contrast to splenocytes, LPS-, SA-, and GBS-induced TNF-, IL-10, and thromboxane B₂ (TxB₂) production was decreased in M harvested from G_i2–/– mice. Also, LPS-induced production of IL-10 and TxB₂ was decreased in M from G_i1/3–/– mice. In subsequent in vivo studies, TNF- levels after LPS challenge were significantly greater in G_i2–/– mice than in WT mice. Also, myeloperoxidase activity, a marker of tissue neutrophil infiltration, was significantly increased in the gut and lung of LPS-treated G_i2–/– mice compared with WT mice. These data suggest that G_i proteins differentially regulate murine TLR-mediated inflammatory cytokine production in a cell-specific manner in response to both LPS and gram-positive microbial stimuli. G_i protein-deficient mice; endotoxin; group B streptococci; Staphylococcus aureus; Toll-like receptors     

Characterization of G proteins involved in activation of nonselective cation channels and arachidonic acid release by norepinephrine/alpha1A-adrenergic receptors

We demonstrated recently that norepinephrine activates Ca²⁺-permeable nonselective cation channels (NSCCs) in Chinese hamster ovary cells stably expressing _1A-adrenergic receptors (CHO-_1A). Moreover, extracellular Ca²⁺ through NSCCs plays essential roles in norepinephrine-induced arachidonic acid release. The purpose of the present study was to identify the G proteins involved in the activation of NSCCs and arachidonic acid release by norepinephrine. For these purposes, we used U73122, an inhibitor of phospholipase C (PLC), and dominant negative mutants of G₁₂ and G₁₃ (G₁₂G228A and G₁₃G225A, respectively). U73122 failed to inhibit NSCCs activation by norepinephrine. The magnitudes of norepinephrine-induced extracellular Ca²⁺ influx in CHO-_1A microinjected with G₁₃G225A were smaller than those in CHO-_1A. In contrast, the magnitudes of norepinephrine-induced extracellular Ca²⁺ influx in CHO-_1A microinjected with G₁₂G228A were similar to those in CHO-_1A. In addition, neither a Rho-associated kinase (ROCK) inhibitor nor a phosphoinositide 3-kinase inhibitor affected norepinephrine-induced extracellular Ca²⁺ influx. G₁₃G225A, but not G₁₂G228A, also inhibited arachidonic acid release partially. These results demonstrate that 1) the G_q/PLC-pathway is not involved in NSCCs activation by norepinephrine, 2) G₁₃ couples with CHO-_1A and plays important roles for norepinephrine-induced NSCCs activation, 3) neither ROCK- nor PI3K-dependent cascade is involved in NSCCs activation, and 4) G₁₃ is involved in norepinephrine-induced arachidonic acid release in CHO-_1A. norepinephrine; _1A-adrenergic receptor; nonselective cation channel; G₁₃ protein; arachidonic acid release     

Cytosolic pH regulates GCl through control of phosphorylation states of CFTR

Our objective inthis study was to determine the effect of changes in luminal andcytoplasmic pH on cystic fibrosis transmembrane regulator (CFTR)Cl conductance(G_Cl). Wemonitored CFTRG_Cl in the apicalmembranes of sweat ducts as reflected byCl diffusion potentials(V_Cl) andtransepithelial conductance(G_Cl). We foundthat luminal pH (5.0-8.5) had little effect on thecAMP/ATP-activated CFTRG_Cl, showing thatCFTR G_Cl ismaintained over a broad range of extracellular pH in which it functionsphysiologically. However, we found that phosphorylation activation ofCFTR G_Cl issensitive to intracellular pH. That is, in the presence of cAMP and ATP [adenosine5'-O-(3-thiotriphosphate)],CFTR could be phosphorylated at physiological pH (6.8) but not at lowpH (~5.5). On the other hand, basic pH prevented endogenousphosphatase(s) from dephosphorylating CFTR.After phosphorylationof CFTR with cAMP and ATP, CFTRG_Cl is normallydeactivated within 1 min after cAMP is removed, even in the presence of5 mM ATP. This deactivation was due to an increase in endogenousphosphatase activity relative to kinase activity, since it was reversedby the reapplication of ATP and cAMP. However, increasing cytoplasmicpH significantly delayed the deactivation of CFTRG_Cl in adose-dependent manner, indicating inhibition of dephosphorylation. Weconclude that CFTRG_Cl may beregulated via shifts in cytoplasmic pH that mediate reciprocal controlof endogenous kinase and phosphatase activities. Luminal pH probably has little direct effect on these mechanisms. This regulation of CFTRmay be important in shifting electrolyte transport in the duct fromconductive to nonconductive modes.

     

Bumetanide blocks CFTR GCl in the native sweat duct

Bumetanide is wellknown for its ability to inhibit the nonconductiveNa⁺-K⁺-2Clcotransporter. We were surprised in preliminary studies to find thatbumetanide in the contraluminal bath also inhibited NaCl absorption inthe human sweat duct, which is apparently poor in cotransporteractivity. Inhibition was accompanied by a marked decrease in thetransepithelial electrical conductance. Because the cystic fibrosistransmembrane conductance regulator (CFTR) Cl channel is richlyexpressed in the sweat duct, we asked whether bumetanide acts byblocking this anion channel. We found that bumetanide1) significantly increased wholecell input impedance, 2)hyperpolarized transepithelial and basolateral membrane potentials, 3) depolarized apical membranepotential, 4) increased the ratio ofapical-to-basolateral membrane resistance, and5) decreased transepithelialCl conductance(G_Cl).These results indicate that bumetanide inhibits CFTRG_Clin both cell membranes of this epithelium. We excluded bumetanideinterference with the protein kinase A phosphorylation activationprocess by "irreversibly" phosphorylating CFTR [by usingadenosine5'-O-(3-thiotriphosphate) in thepresence of a phosphatase inhibition cocktail] before bumetanideapplication. We then activated CFTRG_Clby adding 5 mM ATP. Bumetanide in the cytoplasmic bath(10³ M) inhibited ~71%of this ATP-activated CFTRG_Cl,indicating possible direct inhibition of CFTRG_Cl.We conclude that bumetanide inhibits CFTRG_Clin apical and basolateral membranes independent of phosphorylation. Theresults also suggest that>10⁵ M bumetanide cannotbe used to specifically block theNa⁺-K⁺-2Cl cotransporter.

     

Studies of Growth and Flowering in Picea sitchensis (Bong.) Carr. 1. Effects of Growth Regulator Applications to Mature Scions on Seedling Rootstocks

Effects of growth regulator applications on the flowering of5-years-grafted mature scions of Picea sitchensis (Bong.) Carr.were assessed. Growth regulators were applied to the bud surfacein droplets of ethanol during July, August and September ina polythene house or glasshouse. A mixture of gibberellins A₄and A₇ applied alone, and in combination with gibberellins A₃and A₅, significantly increased numbers by up to seven timesfor male and by up to eight times for female strobili, gibberellinA, gave relatively the strongest response, and gibberellin A₄was inactive. Phosphon D and abscisic acid each reversed thepromotion of flowering by gibberellins, whilst kinetin and N,N-diphenylureahad no effect. The number of female strobili was negativelycorrelated with vegetative shoot length in the year after treatment. Under field conditions hormones were applied in July and Augustunder flaps of bark on the branches of 10-years-grafted maturescions. Gibberellin applications caused a 5-fold increase inflowering and N⁶-benzyladenine further increased the response.Naphth-lyl-acetic acid reduced female and increased male flowering.Bark removal near the base of the branch further enhanced hormone-inducedstrobilus production. The usefulness of these findings for thebreeding of Picea sitchensis is discussed.     

Variable G2 Duration in Root-Meristem Cells of Vicia faba

Scintillation autoradiography was utilized to demonstrate thevariable duration of G₂ in Vicia faba root meristems. The ratioof the longest (max G) to the shortest (min ) duration was 5.4,with min being approximately 2.5 h.     

Comparative Potency of Nine Gibberellins

Gibberellins A₁ to A₉ have been compared, each at several doselevels, in bioassays based on extension of stems of dwarf gardenpea (Pisum sativum), dwarf bean (Phaseolus vulgaris) and Lunariaannua, of hypocotyls of cucumber (Cucumis sativus) and lettuce(Lactuca sativa), and of leaf sheaths of three dwarf mutants(d–1, d–3, d–5) of maize (Zea mays). GibberellinsA₃ (gibberellic acid) and A₇ are of high potency in most bioassays.A₈ is of negligible potency in all and is probably not a functionalhormone. The other gibberellins show a more or less marked tendencyto specificity. The plants used as bioassay material also differin the specificity of their response. Some, for example, maizedwarfs d–3 and d–5 and lettuce, respond well tomost gibberellins; others, for example, cucumber, respond onlyto a few; extreme specificity is shown by Lunaria annua which,in the unvernalized condition, responds by stem elongation onlyto gibberellin A₇. Dose/response curves of the various gibberellinsare usually parallel, but certain exceptions to this have beenfound. Possible explanations of specificity are discussed inrelation to the results obtained, and it is concluded that insufficientevidence is available to make it possible to draw any validconclusions. Current definitions of gibberellins, whether basedon chemical structure or biological activity, are unsatisfactory.     

A model for phosphocreatine resynthesis

Nevill, Alan M., David A. Jones, David McIntyre, Gregory C. Bogdanis, and Mary E. Nevill. A model forphosphocreatine resynthesis. J. Appl.Physiol. 82(1): 329-335, 1997.A model for phosphocreatine (PCr) resynthesis is proposed based on a simple electric circuit, where the PCr store in muscle is likened to thestored charge on the capacitor. The solution to the second-order differential equation that describes the potential around the circuitsuggests the model for PCr resynthesis is given byPCr(t) = R  [d₁ ^· exp(k₁ ^· t) ± d₂ ^· exp(k₂ ^· t)],where R is PCr concentration at rest,d₁,d₂, k₁, andk₂ are constants, andt is time. By using nonlinear leastsquares regression, this double-exponential model was shown to fit thePCr recovery data taken from two studies involving maximal exerciseaccurately. In study 1, when themuscle was electrically stimulated while occluded, PCr concentrations rose during the recovery phase to a level above that observed at rest.In study 2, after intensive dynamicexercise, PCr recovered monotonically to resting concentrations. Thesecond exponential term in the double-exponential model was found tomake a significant additional contribution to the quality of fit inboth study 1 (P < 0.05) andstudy 2 (P < 0.01).

     

Pyruvate and citric acid cycle carbon requirements in isolated skeletal muscle mitochondria

Carbohydrate depletion precipitates fatigue in skeletal muscle, but, because pyruvate provides both acetyl-CoA for mainline oxidation and anaplerotic carbon to the citric acid cycle (CAC), the mechanism remains obscure. Thus pyruvate and CAC kinetic parameters were independently quantified in mitochondria isolated from rat mixed skeletal muscle. Mitochondrial oxygen consumption rate (J_o) was measured polarographically while either pyruvate or malate was added stepwise in the presence of a saturating concentration of the other substrate. These substrate titrations were carried out across a physiological range of fixed extramitochondrial ATP free energy states (G_P), established with a creatine kinase energy clamp, and also at saturating [ADP]. The apparent K_m,malate for mitochondrial J_o ranged from 21 to 32 µM, and the apparent K_m,pyruvate ranged from 12 to 26 µM, with both substrate K_m values increasing as G_P declined. V_max for both substrates also increased as G_P fell, reflecting thermodynamic control of J_o. Reported in vivo skeletal muscle [malate] are >10-fold greater than the K_m,malate determined in this study. In marked contrast, the K_m,pyruvate determined is near the [pyruvate] reported in muscle approaching exhaustion associated with glycogen depletion. When data were evaluated in the context of a linear thermodynamic force-flow (G_P-J_o) relationship, the G_P-J_o slope was essentially insensitive to changes in [malate] in the range observed in vivo but decreased markedly with declining [pyruvate] across the physiological range. Mitochondrial respiration is particularly sensitive to variations in [pyruvate] in the physiological range. In contrast, physiological [malate] exerts very little, if any, influence on mitochondrial pyruvate oxidation measured in vitro. bioenergetics; fatigue; anaplerosis; Krebs cycle; fuel limitation; metabolic control analysis     

The influence of temperature and light on the upper limit of Microcystis aeruginosa production in a hypertrophic reservoir

Primary production was measured for 7 years, using the in situ¹⁴C-method in hypertrophic Hartbeespoort Dam, South Africa,to examine the influence of light and water temperature on theupper limit of Microcystis aeruginosa production. Water temperaturesvaried from 11 to >25°C and chlorophyll concentrationsreached 6500 mg m^–3. The maximum volumetric rate of production(A_max) was 12->8800 mg C m^–3 h^–1 with areal productions(A) of 69->3300 mg C m^–2 h^–1 for euphotic zonedepths of <0.5–8.4 m. The intrinsic parameters of phytoplanktonproduction (, A_max/B, I_k) indicated that the phytoplankton populationwas adapted to high light levels. Both A_max/B and I_k were correlatedwith temperature. Under optimal conditions, , the theoreticalupper limit of A, was calculated to be 2.8 g Cm^–2 h^–1,while the measured rate was 2.5 g Cm^–2 h^–1. Measuredareal rates exceeding were overestimated due to methodologicalproblems when working with Microcystis scums. Light and watertemperature interacted to yield high production rates: watertemperature through its direct effect on photosynthetic ratesand indirectly in the formation of diurnal mixed layers; lightindirectly through water temperature and directly through itsattenuation and induction of light-adapted physiology in Microcystis.     

Ventilation distribution during histamine provocation

Verbanck, S., D. Schuermans, A. Van Muylem, M. Paiva, M. Noppen, and W. Vincken. Ventilation distribution during histamine provocation. J. Appl. Physiol. 83(6):1907-1916, 1997.We investigated ventilation inhomogeneity duringprovocation with inhaled histamine in 20 asymptomatic nonsmokingsubjects. We used N₂multiple-breath washout (MBW) to deriveparameters S_condand S_acin as ameasurement of ventilation inhomogeneity in conductive and acinar zonesof the lungs, respectively. A 20% decrease of forced expiratory volume in 1 s (FEV₁) was used todistinguish responders from nonresponders. In the responder group,average FEV₁ decreased by 26%,whereas S_condincreased by 390% with no significant change inS_acin. In thenonresponder group, FEV₁ decreasedby 11%, whereasS_cond increased by 198% with no significantS_acin change.Despite the absence of change inS_acin duringprovocation, baselineS_acin wassignificantly larger in the responder vs. the nonresponder group. Themain findings of our study are that during provocation largeventilation inhomogeneities occur, that the small airways affected bythe provocation process are situated proximal to the acinar zone wherethe diffusion front stands, and that, in addition to overall decreasein airway caliber, there is inhomogeneous narrowing of parallelairways.

     

Distinct K+ conductive pathways are required for Cl- and K+ secretion across distal colonic epithelium

Secretion of Cl^– and K⁺ in the colonic epithelium operates through a cellular mechanism requiring K⁺ channels in the basolateral and apical membranes. Transepithelial current [short-circuit current (I_sc)] and conductance (G_t) were measured for isolated distal colonic mucosa during secretory activation by epinephrine (Epi) or PGE₂ and synergistically by PGE₂ and carbachol (PGE₂ + CCh). TRAM-34 at 0.5 µM, an inhibitor of K_Ca3.1 (IK, Kcnn4) K⁺ channels (H. Wulff, M. J. Miller, W. Hänsel, S. Grissmer, M. D. Cahalan, and K. G. Chandy. Proc Natl Acad Sci USA 97: 8151–8156, 2000), did not alter secretory I_sc or G_t in guinea pig or rat colon. The presence of K_Ca3.1 in the mucosa was confirmed by immunoblot and immunofluorescence detection. At 100 µM, TRAM-34 inhibited I_sc and G_t activated by Epi (4%), PGE₂ (30%) and PGE₂ + CCh (60%). The IC₅₀ of 4.0 µM implicated involvement of K⁺ channels other than K_Ca3.1. The secretory responses augmented by the K⁺ channel opener 1-EBIO were inhibited only at a high concentration of TRAM-34, suggesting further that K_Ca3.1 was not involved. Sensitivity of the synergistic response (PGE₂ + CCh) to a high concentration TRAM-34 supported a requirement for multiple K⁺ conductive pathways in secretion. Clofilium (100 µM), a quaternary ammonium, inhibited Cl^– secretory I_sc and G_t activated by PGE₂ (20%) but not K⁺ secretion activated by Epi. Thus Cl^– secretion activated by physiological secretagogues occurred without apparent activity of K_Ca3.1 channels but was dependent on other types of K⁺ channels sensitive to high concentrations of TRAM-34 and/or clofilium. epinephrine; prostaglandin E₂; cholinergic; Kcnn4; TRAM-34; clofilium     

Analysis and Significance of Gravity-induced Asymmetric Growth in the Grass Leaf-sheath Pulvinus

The negative gravitropic response in the grass leaf-sheath pulvinusis a consequence of cell elongation involving all cells exceptthose of the uppermost region of the upper flank of an horizontallyoriented pulvinus. The lowermost layer of cells elongate maximally,and the regions in between elongate to intermediate extents.The resulting curvatures of a responding pulvinus can be expressedmathematically by relating the angle of curvature () to theoriginal length (L₀) and the maximal length of the lower surface(L₁) and the diameter of the organ (D), using the equation, = (L₁–L₀)/D, where is in radians. The elongation response(S) of any individual cell within the pulvinus can be expressedby the equation, S = 0.5-r cos, where r is the radius of thepulvinus and is in degrees. Microscopic measurement of celllengths in different regions of the pulvinus supports the mathematicalpredictions. Indirect support is also obtained from the useof colchicine, coumarin, dichloro-benzonitrile (DCBN) and isopropylN-chlorophenyl carbamate which exaggerate the inherent asymmetryduring gravitropic response. Coumarin and DCBN also induce thickeningsin the radial walls which appear first in the statenchyma, andlater, in cells located towards the outer periphery of the pulvinus.The distribution patterns of these thickenings suggest thatthe asymmetric growth response of the pulvinus may be due toa differential and radial, centrifugal transport of growth promotorsfrom the central statenchyma region. Gravity perception, grass pulvinus