β2-Adrenoceptor activation by zinterol causes protein phosphorylation,contractile effects and relaxant effects through a cAMP pathway in human atrium

Evidence from ventricular preparations of cat, sheep, rat and dog suggests that both ₁-adrenoceptors (₁AR) and ₂-adrenoceptors (₂AR) mediate positive inotropic effects but that only ₁AR do it through activation of a cAMP pathway. On the other hand, our evidence has shown that both ₁ AR and ₂ AR hasten relaxation of isolated human myocardium consistent with a common cAMP pathway. We have now investigated in the isolated human right atrial appendage, a tissue whose -AR comprise around 2/3 of ₁AR and 1/3 of ₂AR, whether or not ₂AR-mediated effects occur via activation of a cAMP pathway. We carried out experiments on atria obtained from patients without advanced heart failure undergoing open heart surgery. To activate ₂AR, we used the ₂AR-selective ligand zinterol. Experiments were carried out on paced atrial strips (1 Hz) and tissue homogenates and membrane particles. Zinterol caused positive inotropic and lusitropic (i.e. reduction of t_1:2 of relaxation) effects with EC₅₀ values of 3 and 2 nM, respectively. The zinterol-evoked effects were unaffected by the AR-selective antagonist CGP 20712A (300 nM) but blocked surmountably by the ₂AR-selective antagonist ICI 118551 (50 nM) which reduced both EC₅₀ values to 1 M. Zinterol stimulated adenylyl cyclase activity with an EC₅₀ of 30 nM and intrinsic activity of 0.75 with respect to (–)-isoprenaline (600 M); the effects were resistant to blockade by CGP 20712A (300 nM) but antagonised surmountably by ICI 118551 (50 nM). Zinterol bound to membrane PAR labelled with (–)-[¹²⁵I] cyanopindolol with higher affinity for ₂AR than for - 1 AR; the binding to ₂AR but not to - BAR was reduced by GTPyS (10 M). In the presence of CGP 20712A (300 nM) (–)-isoprenaline (400 M); (to activate both ₁AR and ₂AR maximally) and zinterol (10 M); increased contractile force 3.4-fold and 2.5-fold respectively and reduced relaxation tut by 32% and 18% respectively. These effects of (–)-isoprenaline and zinterol were associated (5 min incubation) with phosphorylation (pmol P/mg supernatant protein) of troponin I and C-protein to values of 8.4 ± 2.0 vs 12.4 ± 2.3 and 10.1 ± 2.5 vs 8.6 ± 1.6 respectively. (–)-Isoprenaline and zinterol also caused phosphorylation of phospholamban (1.8 ± 0.3 vs 0.4 ± 0.1 pmol P/mg respectively) specifically at serine residues. We conclude that in human atrial myocardium activation of both ₁AR and ₂AR leads to cAMP-dependent phosphorylation of proteins involved in augmenting both contractility and relaxation.     

The Kinetics of N-Ethylmaleimide Inhibition of a Vacuolar H+-ATPase and Determination of Nucleotide Dissociation Constants

All eukaryotic vacuolar (V-type) ATPases share the property of being inhibited by low concentrations (1-2 [mu]M) if N-ethylmaleimide (NEM). This distinguishes them from P-type ATPases, which are inhibited by higher concentrations of NEM (0.1-1 mM), and F-type ATPases, which are virtually resistant to inhibition by NEM. Using tonoplast vesicles from Beta vulgaris we have determined the kinetics of NEM inactivation of the V-type ATPase to be pseudo-first order. The concentration dependence of the reaction indicates interaction with a single class of inhibitory site with a rate constant of 4.1 x 104 M-1 min-1. Nucleotides protect against inactivation with an efficacy that agrees with their capacity to act as enzyme substrates. The dissociation constant for MgATP has been determined from protection experiments to be 0.44 mM, which is close to the observed Km for hydrolysis (0.39 mM). Likewise, the dissociation constant for protection by MgADP (127 [mu]M) is close to its inhibition constant as a competitive inhibitor (110 [mu]M). Taken together, these findings suggest that NEM inactivation is associated with nucleotide protectable exposure of a single cysteine residue on the catalytic subunit and confirm the utility of this residue for the determination of ligand dissociation constants through protection of maleimide inhibition.     

The Physiological Relevance of Na+-Coupled K+-Transport

Plant roots utilize at least two distinct pathways with high and low affinities to accumulate K+. The system for high-affinity K+ uptake, which takes place against the electrochemical K+ gradient, requires direct energization. Energization of K+ uptake via Na+ coupling has been observed in algae and was recently proposed as a mechanism for K+ uptake in wheat (Triticum aestivum L.). To investigate whether Na+ coupling has general physiological relevance in energizing K+ transport, we screened a number of species, including Arabidopsis thaliana L. Heynh. ecotype Columbia, wheat, and barley (Hordeum vulgare L.), for the presence of Na+-coupled K+ uptake. Rb+-flux analysis and electrophysiological K+-transport assays were performed in the presence and absence of Na+ and provided evidence for a coupling between K+ and Na+ transport in several aquatic species. However, all investigated terrestrial species were able to sustain growth and K+ uptake in the absence of Na+. Furthermore, the addition of Na+ was either without effect or inhibited K+ absorption. The latter characteristic was independent of growth conditions with respect to Na+ status and pH. Our results suggest that in terrestrial species Na+-coupled K+ transport has no or limited physiological relevance, whereas in certain aquatic angiosperms and algae this type of secondary transport energization plays a significant role.     

Calcineurin,a Type 2B Protein Phosphatase,Modulates the Ca2+-Permeable Slow Vacuolar Ion Channel of Stomatal Guard Cells

The slowly activating vacuolar (SV) channel of plant vacuoles is gated open by cytosolic free Ca2+ and by cytosol-positive potentials. Using vacuoles isolated from broad bean guard cell protoplasts, SV-mediated currents could be measured in the whole-vacuole configuration of a patch clamp as the time-dependent increase in current at cytosol-positive voltages. Time-dependent deactivation of the SV currents when changing from activating to nonactivating voltages (tail currents) was used to calculate the selectivity of the channel to Ca2+ and Cl- with respect to K+. Changing the equilibrium potential for each permeant ion (Ca2+, Cl-, and K+) at least once for individual vacuoles allowed the relative permeabilities (P) of each of these ions to be calculated in a single experiment. The resulting Pca:Pcl:Pk ratio was close to 3:0.1:1. In accord with its characterization as a weakly selective Ca2+ channel, the SV-mediated current density decreased with increasing Ca2+ activity in the vacuole lumen. SV currents were potently modulated by the Ca2+-dependent, calmodulin-stimulated protein phosphatase 2B (calcineurin). At low concentrations ([less than or equal to]0.4 units per mL), calcineurin stimulated SV currents by ~60%, whereas at higher concentrations the phosphatase was inhibitory, reaching ~90% inhibition at 3 units per mL. Bovine calmodulin had no direct effect on SV-mediated currents, although calcineurin stimulated by exogenous calmodulin inhibited SV currents at all concentrations tested with half-maximal inhibition for calcineurin at 0.16 units per mL. The inhibitory effect of calcineurin could be blocked by the pyrethroid deltamethrin, indicating inhibition of SV channels by calcineurin via dephosphorylation. A model is discussed in which vacuolar Ca2+ release through SV channels is subject to both positive feedforward and negative feedback control through cytosolic Ca2+ and dephosphorylation, respectively.     

Localization of nitric oxide synthase in canine ileocolonic and pyloric sphincters

The distribution of neurons containing NADPH-diaphorase (NADPH-d) activity and nitric oxide synthase-like immunoreactivity (NOS-LI) in the canine pyloric and ileocolonic sphincters was studied. Cells within the myenteric and submucosal ganglia were positive for NADPH-d. These cells generally had the morphology of Dogiel type-I enteric neurons, however, there was some diversity in the morphology of NADPH-d-positive neurons in the myenteric plexus of the pylorus. Intramuscular ganglia were observed in both sphincters, and NADPH-d was found in a sub-population of neurons within these ganglia. Dual staining with an antiserum raised against nitric oxide synthase (NOS) demonstrated that almost all cells with NOS-LI were also NADPH-d positive. Varicose fibers within ganglia and within the circular and longitudinal muscle layers also possed NOS-LI and NADPH-d activity. Dual staining with anti-VIP antibodies showed that some of the NADPH-d-positive cells in the myenteric and submucosal ganglia also contained VIP-LI, but all VIP-LI-positive cells did not express NADPH-d activity. These data are consistent with recent physiological studies suggesting that nitric oxide serves as an inhibitory neurotransmitter in the pyloric and ileocolonic sphincters. The data also suggest that VIP is expressed in a sub-population of NADPH-d-positive neurons and may therefore act as a co-transmitter in enteric inhibitory neurotransmission to these specialized muscular regions.     

Accumulation of selenium in a model freshwater microbial food web.

The transfer of selenium between bacteria and the ciliated protozoan, Paramecium putrinum, was examined in laboratory cultures. The population growth of the ciliate was not inhibited in the presence of the highest concentrations of dissolved selenite or selenate tested (10(3) micrograms liter-1). Experiments with radioactive 75selenite or 75selenate indicated that accumulation of selenium by ciliates through time was low when feeding and metabolism were reduced by incubating at 0 degrees C. However, selenium accumulated in ciliate biomass during incubation with dissolved 75Se and bacteria at 24 degrees C and also when bacteria prelabeled with 75Se were offered as food in the absence of dissolved selenium. When 75Se-labeled bacterial food was diluted by the addition of nonradioactive bacteria, the amount of selenite and selenate in ciliates decreased over time, indicating depuration by the ciliates. In longer-term (> 5-day) fed-batch incubations with 75selenite-labeled bacteria, the selenium concentration in ciliates equilibrated at approximately 1.4 micrograms of Se g (dry weight)-1. The selenium content of ciliates was similar to that of their bacterial food on a dry-weight basis. These data indicate that selenium uptake by this ciliate occurred primarily during feeding and that biomagnification of selenium did not occur in this simple food chain.     

Chloroflexus-like organisms from marine and hypersaline environments: Distribution and diversity

We report the presence of a diverse number ofChloroflexus-like organisms in intertidal marine and submerged hypersaline microbial mats using light, infrared fluorescence, and electron microscopy. The intertidal organisms appear morphologically very similar to thermophilicC. aurantiacus while the 2 hypersaline strains are larger and have a more complex ultrastructure composed of chlorosome-bearing internal membranes that appear to arise as invaginations of the cell membrane. By comparing spectroradiometry of microbial mat layers with microscopic observations, we have confirmed that theChloroflexus-like organisms are major constituents of the hypersaline microbial mat communities. In situ studies on mat layers dominated byChloroflexus-like organisms showed that sulfide-dependent photoautotrophic activity sustained by near infrared radiation prevailed. Autoradiographic analyses revealed that autotrophy was sustained in the filaments by 750 nm radiation. Three morphologically distinct strains are now maintained in mixed culture. One of these appears to be growing photoautotrophically.     

Smoking and cancer: smoking cessation.

Smoking is the single most important cause of cancer. The risk of developing cancer is reduced by stopping smoking and decreases substantially after five years. Reduction in smoking must be central to any programme aimed seriously at the prevention of cancer. An individual approach, based in primary care, has the potential to bring about modest but important reductions in risk. Many randomised trials have shown the effectiveness of various smoking cessation interventions in primary care. Given resource limitations in primary care, individual effort should be focused on those at highest risk who are motivated to stop smoking. A population strategy has considerable advantages over the high risk approach as the potential for reducing morbidity and mortality in the whole population is much greater. The government must acknowledge its major responsibility; the outstanding example of its failure to do this is its persistent refusal to ban outright all forms of advertising and promotion of tobacco. There is clear evidence that a ban would contribute to a reduction in smoking prevalence and especially in the uptake of smoking by children.     

Studies on the production of human parathyroid hormone by recombinant Escherichia coli

Expression of human parathyroid hormone, hPTH(-1-84), by Escherichia coli N4830: pEX-PPTH was studied in controlled bioreactors. The hPTH is expressed as a fusion protein under control of the bacteriophage p_R promoter. In batch runs, low biomass concentrations but high specific hPTH productivities were obtained with complex TY (bactotryptone and yeast extract) medium whereas high biomass concentration and low specific productivities were found when fructose was used instead of bactotryptone (YF medium). The preinduction temperature was always 30°C; the temperature shift to induce production of fusion protein was varied from 36 to 42°C. Formation of hPTH passed a pronounced maximum as a function of induction temperature when using YF medium. However, the optimum temperature shift was 38°C for both media used. For this temperature increase both media yielded about the same volumetric hPTH productivity (approx. 30 mg hPTH/l per hour). By applying a fedbatch strategy for the YF medium, the productivity of the recombinant protein could be further increased more than fourfold. Compared to shake-flask experiments, the hPTH yield could be increased by a factor larger than 20.     

Two Voltage-Gated,Calcium Release Channels Coreside in the Vacuolar Membrane of Broad Bean Guard Cells

Voltage-gated, Ca2+ release channels have been characterized at the vacuolar membrane of broad bean guard cells using patch clamps of excised, inside-out membrane patches. The most prevalent Ca2+ release channel had a conductance of 27 pS over voltages negative of the reversal potential (Erev) (cytosol referenced to vacuole), with 5,10, or 20 mM Ca2+ as the charge carrier on the vacuolar side and 50 mM K+ on the cytosolic side. The single-channel current saturated at ~2.6 pA. The relative permeability of the channel was in the range of a Pca2+:Pk+ ratio of 6:1. Divalent cations could act as charge carriers on the vacuolar side with a conductance series of Ba2+ > Mg2+ > Sr2+ > Ca2+ and a selectivity sequence of Ca2+ [approximately equals to] Ba2+ [approximately equals to] Sr2+ > Mg2+. The channel was gated open by cytosol-negative (physiological) transmembrane voltages, increases in vacuolar Ca2+ concentration, and increases in the vacuolar pH. The channel was potently inhibited by the Ca2+ channel blockers Gd3+ (half-maximal inhibition at 10.3 [mu]M) and nifedipine (half-maximal inhibition at 77 [mu]M). The stilbene derivative 4,4[prime]-diisothiocyano-2,2[prime]-stilbene disulfonate was also inhibitory (half-maximal inhibition for a 4-min incubation period at 6.3[mu]M). The 27-pS channel coresides in individual guard cell vacuoles with a less frequently observed 14-pS Ca2+ release channel that had similar, although not identical, voltage dependence and gating characteristics and a lower selectivity for Ca2+ over K+. The requirement for two channels with a similar function at the vacuolar membrane of guard cells is discussed.