Growth Stimulation of Iodide-Oxidizing α-<Emphasis Type="Italic">Proteobacteria</Emphasis> in Iodide-Rich Environments

α-Proteobacteria that can oxidize iodide (I⁻) to molecular iodine (I₂) have only been isolated from iodide-rich natural and artificial environments, i.e., natural gas brine waters and seawaters supplemented with iodide, respectively. To understand the growth characteristics of such iodide-oxidizing bacteria (IOB) under iodide-rich environments, microcosms comprising natural seawater and 1 mM iodide were prepared, and the succession of microbial communities was monitored by culture-independent techniques. PCR-denaturing gradient gel electrophoresis and 16S rRNA gene sequence analysis showed that bacteria closely related with known IOB were predominant in the microcosms after several weeks of incubation. Quantitative PCR analysis targeting specific 16S rRNA gene regions of IOB showed that the relative abundance of IOB in the microcosms was 6–76% of the total bacterial population, whereas that in natural seawater was less than 1%. When 10³ cells mL⁻¹ of IOB were inoculated into natural seawater supplemented with 0.1–1 mM iodide, significant growth (cell densities, 10⁵–10⁶ cells mL⁻¹) and I₂ production (6–32 μM) were observed. Interestingly, similar growth stimulation occurred when 12–44 μM of I₂ was added to seawater, instead of iodide. IOB were found to be more I₂ tolerant than the other heterotrophic bacteria in seawater. These results suggest that I₂ plays a key role in the growth stimulation of IOB in seawater. IOB could potentially attack other bacteria with I₂ to occupy their ecological niche in iodide-rich environments.     

COMPONENTS OF PHOTOSYNTHESIS IN THE INTERTIDAL SACCATE ALGA HALOSACCION AMERICANUM (RHODOPHYTA,PALMARIALES)1

Rates of photosynthesis for the intertidal saccate alga Halosaccion americanum Lee were determined under submersed and emersed conditions. By fitting the data to a hyperbolic tangent function, P _max was 4.08 mmol CO₂. m^?2. h^?1 and I_k was 116.4 μE. m^?2. s^?1. under submersed conditions. Under emersed conditions, P _max was 1.89 mmol CO₂. m^?2. h^?1 and I_k was 22.9 μE. m^?2. s^?1. Dark fixation represented 3.7% of P_max in submersed thalli, whereas it equalled 33.3% of P_max in emersed thalli. Photosynthetic uptake from the thallus cavity represented a significant source of carbon, achieving 68.8% of that from the atmosphere and 29.4% of that from seawater. Retained seawater also greatly reduced drying under emersed conditions. Experimental thalli lost 70.4% of their water after 120 min under desiccating conditions, whereas control thalli lost only 6.3%. Emersed photosynthetic rates were enhanced by desiccation, At times, rates for desiccated thalli were two times those of fully-hydrated ones. Only after water loss exceeded 47% did photosynthetic rates fall below fully-hydrated rates. Utilizing data from this study a model was constructed to determine total photosynthetic production of H. americanum over a single daylight period. These caluclations demonstrate that photosynthetic contributions from emersed photosynthesis and retained seawater are significant. Because production from all sources is almost equal, total photosynthesis over a single day does not change greatly regardless of the time spent in air or in water.     

Active NaCl absorption across split lamellae of posterior gills of Chinese crabs (Eriocheir sinensis) adapted to different salinities

Split lamellae of posterior gills of Eriocheir sinensis adapted to fresh water, brackish waters (9 or 18‰) or seawater (36‰) were mounted in Ussing chambers, and transepithelial short-circuit currents and conductances were measured with salines, containing approximately in vivo-like NaCl concentrations. Active sodium and chloride absorption (I_Na and I_Cl), the transcellular conductances and the leak conductance were identified with external amiloride and/or DIDS. Split gill lamellae of crabs adapted to fresh water displayed similar magnitudes of I_Na and I_Cl with 10 mmol l⁻¹ NaCl in the external medium (internally haemolymph-like NaCl saline). Augmenting external NaCl (50 mmol l⁻¹) resulted in an increase of I_Cl, whereas I_Na decreased. Split gill lamellae of crabs adapted to brackish waters (external NaCl of 125 and 225 mmol l⁻¹, respectively) showed lower currents than preparations of freshwater crabs (50 mmol l⁻¹ external NaCl). With split gill lamellae of seawater crabs no currents were detected (450 mmol l⁻¹ NaCl on both sides). The transcellular conductances showed similar changes as the currents. The leak conductance of split gill lamellae of crabs adapted to fresh or brackish waters was low (0.3–0.8 mS cm⁻²), whereas it was much higher (7 mS cm⁻²) with preparations of seawater crabs.     

Methyl mercury inhibits short-circuit current and Cl− influx across isolated epipodite of European lobster (Homarus gammarus)

The effect of methyl mercuric chloride (MeHg) on short-circuit current (I_SC) was studied in the isolated perfused epipodite preparation from the branchial chamber of European lobster (Homarus gammarus) acclimated to dilute seawater. When applied at the apical surface, 0.2, 1.0 and 3.0 μM MeHg depressed I_SC by a 26%, 81% and 98%, respectively. The half-maximal inhibitory concentration (IC₅₀) of apically applied MeHg was 0.6 μM. Basolaterally added MeHg (3.0 μM) had no effect on I_SC, whereas addition of the specific Na⁺,K⁺-ATPase inhibitor ouabain (1.5 mM) reduced I_SC by ～ 90%. Ouabain effects were reversible, and I_SC fully recovered upon removal of ouabain. The MeHg-induced block of I_SC was partially reversed by the reducing agent, 1,4-dithiothreitol, suggesting that the formation of S–Hg–S bridges is important in the inhibitory mechanism. A significant reduction of I_SC and conductance occurred when low Na⁺ and Cl^? salines were substituted. Furthermore, in the low Na⁺ saline, J^Cl_A → B fluxes were reduced by about 50%. In the highly conductive epipodite epithelium, coupling of Na⁺ and Cl^? fluxes was suggested. The effects of MeHg on I_SC in the lobster epipodite are attributed to inhibition of an apical Cl^? influx.     

Effect of concentration of iodide on the bound species of I2/I−3 in the amylose-iodine complex

A liquid-liquid distribution method, with heptane as the organic solvent, involving evaluation of the concentration of free 1⁻ by magnetic circular dichroism, has been developed for determining the bound amounts of I₂/I⁻₃ in the amylose-iodine complex in unbuffered aqueous solutions. The effect of I₂ and I⁻ concentrations on the bound species of iodine in the complex was investigated by using this method. We found that the stoichiometric bound species of I₂/I⁻₃ is independent of the concentration of I₂ at a given I⁻ concentration. However, the bound species strongly depends on I⁻ concentration, and varies from I⁻₃ at 10 mM KI to I⁻₁₅ at 0M KI. Moreover, the number of d-glucosyl residues required for including one iodine atom is within the range of 2.7 to 3.0, regardless of I⁻ concentration. It was concluded that the bound species are governed by the distribution of the actual species I₂·I₂ (I₄), (I₄), I₂·I⁻₃ (I⁻₅), and I⁻₃·I⁻₃ (I²⁻₆), which are responsible for the blue color of the complex.     

Regulation of Ca2+ signaling by acute hypoxia and acidosis in cardiomyocytes derived from human induced pluripotent stem cells

AimsThe effects of acute (100 s) hypoxia and/or acidosis on Ca²⁺ signaling parameters of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) are explored here for the first time.Methods and results1) hiPSC-CMs express two cell populations: rapidly-inactivating I_Ca myocytes (τ_i<40 ms, in 4–5 day cultures) and slowly-inactivating I_Ca (τ_i ≥ 40 ms, in 6–8 day cultures). 2) Hypoxia suppressed I_Ca by 10–20% in rapidly- and 40–55% in slowly-inactivating I_Ca cells. 3) Isoproterenol enhanced I_Ca in hiPSC-CMs, but either enhanced or did not alter the hypoxic suppression. 4) Hypoxia had no differential suppressive effects in the two cell-types when Ba²⁺ was the charge carrier through the calcium channels, implicating Ca²⁺-dependent inactivation in O₂ sensing. 5) Acidosis suppressed I_Ca by ∼35% and ∼25% in rapidly and slowly inactivating I_Ca cells, respectively. 6) Hypoxia and acidosis suppressive effects on Ca-transients depended on whether global or RyR2-microdomain were measured: with acidosis suppression was ∼25% in global and ∼37% in RyR2 Ca²⁺-microdomains in either cell type, whereas with hypoxia suppression was ∼20% and ∼25% respectively in global and RyR2-microdomaine in rapidly and ∼35% and ∼45% respectively in global and RyR2-microdomaine in slowly-inactivating cells.ConclusionsVariability in I_Ca inactivation kinetics rather than cellular ancestry seems to underlie the action potential morphology differences generally attributed to mixed atrial and ventricular cell populations in hiPSC-CMs cultures. The differential hypoxic regulation of Ca²⁺-signaling in the two-cell types arises from differential Ca²⁺-dependent inactivation of the Ca²⁺-channel caused by proximity of Ca²⁺-release stores to the Ca²⁺ channels.     

Solid-state and solution conformation of scleroglucan

A potentiometric-titration procedure, in which samples are always exposed to an excess of I₂-KI has been developed for measuring iodine-binding capacity of starches. Binding capacity of amylose under these conditions is ～30% as opposed to 20% by conventional potentiometric titration. Spectrophotometric absorbance is essentially the same for either method, but is proportional to potentiometric values only in the excess-iodine titration procedure. Effects of variation of concentration of I₂, KI, and phosphate buffer and of temperature on the reaction have been examined. Calculations based on concentration of reactants in solution indicate that the binding species varies from I₃^? at 10^?1m KI to I₁₁^? at 5 × 10^?4m KI.     

Interaction of galantamine with ionic channels in molluscan neurons

Galantamine is widely used for the treatment of Alzheimer’s disease. According to the generally accepted viewpoint, its therapeutic effect is based on inhibition of acetylcholinesterase (AChE) and potentiation of nicotinic receptors. Alternative molecular targets for galanatamine, namely, voltage-gated Ca²⁺ and K⁺ channels of the neuronal membrane, are also widely discussed in the current literature. The present study is devoted to the analysis of effects of galantamine on high-threshold Ca²⁺ currents (I _Ca) and three different kinds of highthreshold K⁺ current, viz.: Ca²⁺-dependent K⁺ current (I _C), delayed rectifier (I _DR), and fast-inactivating K₊ current (I _Adepol). Experiments were conducted on molluscan neurons with the help of two-microelectrode voltageclamp technique. It was found that galantamine caused a fast, reversible and dose-dependent suppression of all types of high-threshold ionic currents. The maximal blocking effect of the alkaloid for I _Ca, I _C, and I _DR, was 100%, while for I Adepol the maximal suppression was only 60%. The mean values of IC ₅₀ for I _C, I _DR, I _Adepol, and I _Ca were 109, 237, 66, and 515 μ M, respectively, i.e., substantially higher than the corresponding values for the alkaloid-induced inhibition of AChE and potentiation of nicotinic receptors. It is concluded that the blockade of Ca₂₊ and K₊ channels has little or no contribution to the therapeutic activity of galantamine.     

Suppression of L-type Ca current by fluid pressure in rat ventricular myocytes: Possible role of Cl–OH exchange

The application of fluid pressure (FP) in ventricular myocytes using pressurized fluid flow inhibits L-type Ca²⁺ current (I_Ca), with approximately 80% of this effect coming through the enhancement of Ca²⁺ releases from the sarcoplasmic reticulum. In the present study, we explored the remaining mechanisms for the inhibition of I_Ca by FP. Since FP significantly increases H⁺ concentration and H⁺ is known to inhibit I_Ca, we examined whether pH regulation plays a role in the inhibitory effect by FP on I_Ca. A flow of pressurized (∼16.3 dyne/cm²) fluid, identical to that bathing the myocytes, was applied onto single rat ventricular myocytes for which the I_Ca was monitored using whole-cell patch-clamp under HEPES-buffered conditions. Extracellular application of the alkalizing agent, NH₄Cl (20 mM), enhanced I_Ca by ∼34% in the control conditions while increasing I_Ca significantly less (by ∼21%) in FP-pretreated myocytes, suggesting an inhibition of the effect of NH₄Cl on I_Ca possibly by FP-induced acidosis. Application of DIDS (4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid, 500 μM), which blocks exchange but not Cl⁻–OH⁻ exchange, did not alter the inhibitory effect of FP on I_Ca. Replacement of external Cl⁻ with aspartate attenuated the inhibitory effect of FP on I_Ca. In highly Ca²⁺-buffered cells, where Ca²⁺-dependent inhibition of I_Ca was minimized, the external Cl⁻ removal eliminated the inhibitory effect of FP on I_Ca. These results suggest that the decrease of I_Ca in the presence of FP is at least partly caused by intracellular acidosis via activation of Cl⁻–OH⁻ exchange in rat ventricular myocytes.     

A Voltage-Dependent Ca<Superscript>2+</Superscript> Influx Pathway Regulates the Ca<Superscript>2+</Superscript>-Dependent Cl<Superscript>−</Superscript> Conductance of Renal IMCD-3 Cells

We have previously shown that the membrane conductance of mIMCD-3 cells at a holding potential of 0 mV is dominated by a Ca²⁺-dependent Cl⁻ current (I_CLCA). Here we report that I_CLCA activity is also voltage dependent and that this dependence on voltage is linked to the opening of a novel Al³⁺-sensitive, voltage-dependent, Ca²⁺ influx pathway. Using whole-cell patch-clamp recordings at a physiological holding potential (−60 mV), I_CLCA was found to be inactive and resting currents were predominantly K⁺ selective. However, membrane depolarization to 0 mV resulted in a slow, sigmoidal, activation of I_CLCA (T _0.5 ~ 500 s), while repolarization in turn resulted in a monoexponential decay in I_CLCA (T _0.5 ~ 100 s). The activation of I_CLCA by depolarization was reduced by lowering extracellular Ca²⁺ and completely inhibited by buffering cytosolic Ca²⁺ with EGTA, suggesting a role for Ca²⁺ influx in the activation of I_CLCA. However, raising bulk cytosolic Ca²⁺ at −60 mV did not produce sustained I_CLCA activity. Therefore I_CLCA is dependent on both an increase in intracellular Ca²⁺ and depolarization to be active. We further show that membrane depolarization is coupled to opening of a Ca²⁺ influx pathway that displays equal permeability to Ca²⁺ and Ba²⁺ ions and that is blocked by extracellular Al³⁺ and La³⁺. Furthermore, Al³⁺ completely and reversibly inhibited depolarization-induced activation of I_CLCA, thereby directly linking Ca²⁺ influx to activation of I_CLCA. We speculate that during sustained membrane depolarization, calcium influx activates I_CLCA which functions to modulate NaCl transport across the apical membrane of IMCD cells.     

Aerosol OT/Water System Coupled with Triiodide/Iodide (I3−/I−) Redox Electrolytes for Highly Efficient Dye‐Sensitized Solar Cells

Dye‐sensitized solar cells (DSCs) are considered to be a promising alternative to Si‐based photovoltaic cells. The electrolyte of the DSC primarily uses triiodide/iodide (I₃^?/I^?) as a redox couple. Therefore, it is essential to understand the regeneration and recombination kinetics of the I₃^?/I^? redox couples in the device. In this context, controlling the total and local concentrations of the I₃^?/I^? redox couples is an important parameter that can influence the DSC performance. Here, we propose that the introduction of a sodium bis (2‐ethylhexyl) sulfosuccinate (AOT)/water system to the I₃^?/I^? electrolyte enables the control of the concentration of the redox couples, which consequently achieves a high power conversion efficiency of ～11% for ～1000 h (under 1 sun illumination) owing to the enhanced dye‐regeneration efficiency and the reduced recombination rate. This novel concept assists in the comprehension of the regeneration and recombination kinetics and develops highly efficient DSCs.     

Potassium Currents in Freshly Dissociated Uterine Myocytes from Nonpregnant and Late-Pregnant Rats

In freshly dissociated uterine myocytes, the outward current is carried by K⁺ through channels highly selective for K⁺. Typically, nonpregnant myocytes have rather noisy K⁺ currents; half of them also have a fast-inactivating transient outward current (I_TO). In contrast, the current records are not noisy in late pregnant myocytes, and I_TO densities are low. The whole-cell I_K of nonpregnant myocytes respond strongly to changes in [Ca²⁺]_o or changes in [Ca²⁺]_i caused by photolysis of caged Ca²⁺ compounds, nitr 5 or DM-nitrophene, but that of late-pregnant myocytes respond weakly or not at all. The Ca²⁺ insensitivity of the latter is present before any exposure to dissociating enzymes. By holding at −80, −40, or 0 mV and digital subtractions, the whole-cell I_K of each type of myocyte can be separated into one noninactivating and two inactivating components with half-inactivation at approximately −61 and −22 mV. The noninactivating components, which consist mainly of iberiotoxin-susceptible large-conductance Ca²⁺-activated K⁺ currents, are half-activated at 39 mV in nonpregnant myocytes, but at 63 mV in late-pregnant myocytes. In detached membrane patches from the latter, identified 139 pS, Ca²⁺-sensitive K⁺ channels also have a half-open probability at 68 mV, and are less sensitive to Ca²⁺ than similar channels in taenia coli myocytes. Ca²⁺-activated K⁺ currents, susceptible to tetraethylammonium, charybdotoxin, and iberiotoxin contribute 30–35% of the total I_K in nonpregnant myocytes, but <20% in late-pregnant myocytes. Dendrotoxin-susceptible, small-conductance delayed rectifier currents are not seen in nonpregnant myocytes, but contribute ∼20% of total I_K in late-pregnant myocytes. Thus, in late-pregnancy, myometrial excitability is increased by changes in K⁺ currents that include a suppression of the I_TO, a redistribution of I_K expression from large-conductance Ca²⁺-activated channels to smaller-conductance delayed rectifier channels, a lowered Ca²⁺ sensitivity, and a positive shift of the activation of some large-conductance Ca²⁺-activated channels.     

BIOCHEMICAL STRATEGIES FOR GROWTH OF GRACILARIA TIKVAHIAE (RHODOPHYTA) IN RELATION TO LIGHT INTENSITY AND NITROGEN AVAILABILITY1

The main effects and interactions between light (I_o, full incident sunlight to 0.07 I_o) and NO₃^? loading (0.4 to 4.3 mmol · g dry weight^?1· d^?1) on growth rate, photosynthesis and biochemical constituents of Gracilaria tikvahiae McLachlan were studied using a factorial design experiment in outdoor, continuous-flow seawater cultures. Incipient nitrogen limitation in the low NO₃^? loading, I_o and 0.57 I_o treatments occurred after 2.5 weeks of growth under the experimental conditions and resulted in decreased tissue NO₃^? and R-phycoerythrin. Tissue NO₃^? and R-phycoerythrin accounted for up to ca. 15 and 20%, respectively, of the total N in G. tikvahiae suggesting a N reserve role for these N pools. Under light and NO₃^? limitation, growth rate was a parabolic function of the C:N ratio. As light limitation increased, growth rate and the C:N ratio decreased as levels of Chl-a, R-phycoerythrin, percent N and percent protein increased. As NO₃^? limitation increased, growth rate and levels of Chl-a, R-phycoerythrin, percent N and percent protein all decreased with parallel increases in the C:N ratio. In contrast to the inverse relationship between pigment content and light, ribulose bisphosphate carboxylase (RuBPCase) activity (on both a protein and dry weight basis) varied directly with light. This biochemical acclimation of G. tikvahiae to light and N availability appears to be a process directed towards maximizing photo synthetic capacity and growth.     

Different tissue responses for iodine and iodide in rat thyroid and mammary glands

This research describes the effects of short-term elemental iodine (I₂) and iodide (I⁻) replacement on thyroid glands and mammary glands of iodine-deficient (ID) Sprague-Dawley female rats. Iodine deficiency causes atypical tissue and physiologic changes in both glands. Tissue histopathology and the endocrine metabolic parameters, such as serum TT₄, tissue and body weights, and vaginal smears, are compared. A moderate reduction in thyroid size from the ID control (IDC) was noted with both I⁻ and I₂, whereas serum total thyroxine approached the normal control with both I⁻ and I₂, but was lower in IDC. Thyroid gland IDC hyperplasia was reduced modestly with I₂, but eliminated with I⁻. Lobular hyperplasia of the mammary glands decreased with I₂ and increased with I⁻ when compared with the IDC; extraductal secretions remained the same as IDC with I₂, but increased with I⁻; and periductal fibrosis was markedly reduced with I₂, but remained severe with I⁻. Thus, orally administered I₂ or I⁻ in trace doses with similar iodine availability caused different histopathological and endocrine patterns in thyroid and mammary glands of ID rats. The significance of this is that replacement therapy with various forms of iodine are tissue-specific.     

Irradiance stress responses of gas exchange and antioxidant enzyme contents in pariparoba [<Emphasis Type="Italic">Pothomorphe umbellata</Emphasis> (L.) Miq.] plants

We evaluated the growth and development of the medicinal species Pothomorphe umbellata (L.) Miq. under different shade levels (full sun and 30, 50, and 70 % shade, marked as I₁₀₀, I₇₀, I₅₀, and I₃₀, respectively) and their effects on gas exchange and activities of antioxidant enzymes. Photosynthetically active radiation varied from 1 254 μmol m⁻² s⁻¹ at I₁₀₀ to 285 μmol m⁻² s⁻¹ at I₃₀. Stomatal conductance, net photosynthetic rate, and relative chlorophyll (Chl) content were maximal in I₇₀ plants. Plants grown under I₁₀₀ produced leaves with lower Chl content and signs of chlorosis and necrosis. These symptoms indicated Chl degradation induced by the generation of reactive oxygen species. Stress related antioxidant enzyme activities (Mn-SOD, Fe-SOD, and Cu/Zn-SOD) were highest in I₁₀₀ plants, whereas catalase activity was the lowest. Hence P. umbellata is a shade species (sciophyte), a feature that should be considered in reforestation programs or in field plantings for production of medicinal constituents.     

A computational study of the role of spike broadening in synaptic facilitation of Hermissenda

Pavlovian conditioning in Hermissenda produces a decrease in voltage-dependent (I_K,A and I_Ca) and Ca²⁺-dependent (I_K,Ca) currents, and an increase in the action potential (AP) duration in type B-photoreceptors. In addition, synaptic connections between B and A photoreceptors and B photoreceptor and type I interneurons are facilitated. The increase in AP duration, produced by decreasing one or more K⁺ currents, may account for synaptic facilitation. The present study examined this issue by using a mathematical model of the B-photoreceptor and the neurosimulator SNNAP. In the model, decreasing g_K,A by 70% increased the duration of the AP in the terminal by 41% and Ca²⁺ influx by 30%. However, if the decrease in g_K,A was combined with a decrease in g_Ca, similar to what has been reported experimentally, the Ca²⁺ influx decreased by 54%. Therefore, the concomitant change in I_Ca counter-acted the broadening-induced increase in Ca²⁺ influx in the synaptic terminal. This result suggests that a spike-duration independent process must contribute to the synaptic facilitation observed following Pavlovian conditioning.     

Microevolutionary trends in the dentition of the Red fox (Vulpes vulpes)

Microevolutionary trends in dental traits were studied in a Polish population of the Red fox, Vulpes vulpes (Linnaeus, 1758). Changes in qualitative and quantitative traits over a 70‐year interval were analysed in 1453 museum specimens collected between 1927 and 1996. Over that period, there were qualitative trends towards increasing complication of occlusal crown surface in posterior premolars (i.e. P⁴, P₃, P₄) and I³. Other cheek teeth did not undergo directional change. Changes in trait correlations were assessed using samples from the 1960s and 1990s. The correlations between C¹–C₁ and M¹–M² increased, while correlation values in the incisor region (I₁–I₂, I¹–I₁, I¹–I₂, I³–I₂), carnassial region (P₄–M₁, P⁴–M₁ and M₁–M₁) and in P²–P₁ decreased. These changes may be related to increasing dietary opportunism of the Red fox during the 20th century.     

Dynamic regulation of guard cell anion channels by cytosolic free Ca2+ concentration and protein phosphorylation

In guard cells, activation of anion channels (I_anion) is an early event leading to stomatal closure. Activation of I_anion has been associated with abscisic acid (ABA) and its elevation of the cytosolic free Ca²⁺ concentration ([Ca²⁺]_i). However, the dynamics of the action of [Ca²⁺]_i on I_anion has never been established, despite its importance for understanding the mechanics of stomatal adaptation to stress. We have quantified the [Ca²⁺]_i dynamics of I_anion in Vicia faba guard cells, measuring channel current under a voltage clamp while manipulating and recording [Ca²⁺]_i using Fura‐2 fluorescence imaging. We found that I_anion rises with [Ca²⁺]_i only at concentrations substantially above the mean resting value of 125 ± 13 nm , yielding an apparent K_d of 720 ± 65 nm and a Hill coefficient consistent with the binding of three to four Ca²⁺ ions to activate the channels. Approximately 30% of guard cells exhibited a baseline of I_anion activity, but without a dependence of the current on [Ca²⁺]_i. The protein phosphatase antagonist okadaic acid increased this current baseline over twofold. Additionally, okadaic acid altered the [Ca²⁺]_i sensitivity of I_anion, displacing the apparent K_d for [Ca²⁺]_i to 573 ± 38 nm . These findings support previous evidence for different modes of regulation for I_anion, only one of which depends on [Ca²⁺]_i, and they underscore an independence of [Ca²⁺]_i from protein (de‐)phosphorylation in controlling I_anion. Most importantly, our results demonstrate a significant displacement of I_anion sensitivity to higher [Ca²⁺]_i compared with that of the guard cell K⁺ channels, implying a capacity for variable dynamics between net osmotic solute uptake and loss.     

Autocrine A2 in the T-System of Ventricular Myocytes Creates Transmural Gradients in Ion Transport: A Mechanism to Match Contraction with Load?

Transmural heterogeneities in Na/K pump current (I_P), transient outward K⁺-current (I_to), and Ca²⁺-current (I_CaL) play an important role in regulating electrical and contractile activities in the ventricular myocardium. Prior studies indicated angiotensin II (A2) may determine the transmural gradient in I_to, but the effects of A2 on I_P and I_CaL were unknown. In this study, myocytes were isolated from five muscle layers between epicardium and endocardium. We found a monotonic gradient in both I_p and I_to, with the lowest currents in ENDO. When AT₁Rs were inhibited, EPI currents were unaffected, but ENDO currents increased, suggesting endogenous extracellular A2 inhibits both currents in ENDO. I_P- and I_to-inhibition by A2 yielded essentially the same K_0.5 values, so they may both be regulated by the same mechanism. A2/AT₁R-mediated inhibition of I_P or I_to or stimulation of I_CaL persisted for hours in isolated myocytes, suggesting continuous autocrine secretion of A2 into a restricted diffusion compartment, like the T-system. Detubulation brought EPI I_P to its low ENDO value and eliminated A2 sensitivity, so the T-system lumen may indeed be the restricted diffusion compartment. These studies showed that 33–50% of I_P, 57–65% of I_to, and a significant fraction of I_CaL reside in T-tubule membranes where they are transmurally regulated by autocrine secretion of A2 into the T-system lumen and activation of AT₁Rs. Increased AT₁R activation regulates each of these currents in a direction expected to increase contractility. Endogenous A2 activation of AT₁Rs increases monotonically from EPI to ENDO in a manner similar to reported increases in passive tension when the ventricular chamber fills with blood. We therefore hypothesize load is the signal that regulates A2-activation of AT₁Rs, which create a contractile gradient that matches the gradient in load.     

Seawater Stress Differentially Affects Germination, Growth, Photosynthesis, and Ion Concentration in Genotypes of Jerusalem Artichoke (Helianthus tuberosus L.)

Two Jerusalem artichoke (Helianthus tuberosus L.) genotypes, NY-1 and NY-7, were subjected to different seawater concentrations (0, 10, 20, 30, 40, and 50%) for various periods of time to determine the effects on seedling growth, ion content, and photosynthetic productivity in a greenhouse. Under different seawater concentrations, sprouting rates varied greatly among the genotypes. The differences in relative growth rate (RGR), leaf chlorophyll content, total leaf area (TLA), plant dry weight (PDW), photosynthetic rate (A), stomatal conductance (g _s), and efficiency of the light harvesting of photosystem II (F _v^′/F _m^′) were significant between NY-1 and NY-7 after 12 days of stress at 40 and 50% seawater. Seawater treatments resulted in the reduction of almost all the growth parameters and coincident increases of Na⁺ and Ca²⁺ concentrations in plant tissues. Our results indicate that there is great variability for seawater tolerance among H. tuberosus varieties, and that greater photosynthesis capacity, higher RGR, and relatively higher tissue Na⁺ accumulation at high seawater concentrations appears to be associated with seawater tolerance in H. tuberosus varieties.