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.     

Fruit set in a deceptive orchid: The effect of flowering phenology,display size,and local floral abundance

We investigated the effect of flowering time, display size, and local floral density on fruit set in Tolumnia variegata, a pollination-limited orchid that offers no reward to its pollinator(s). During 1990, natural variation in flowering time, display size, and fruit set were monitored in 508 plants at one locality in Puerto Rico. The following season, orchid floral abundance per host tree (Randia aculeata) was manipulated to investigate its effect on fruit set. Four floral abundance treatments were established (700, 500, 300, and 100), each replicated four times. Flowering time was the most important trait affecting fruit set. The proportion of plants setting at least one fruit was significantly high early and late in the season, but low during the flowering peak. Thus, strong disruptive selection differential on flowering phenology was found. Display size had little effect on fruit set. A weak, but significant disruptive selection differential on display size was found. Orchid floral abundance per host tree had a significant effect on fruit set. Early in the season, T. variegata flowers with intermediate number of conspecific flowers exhibited a greater probability of setting fruit than those in host trees with fewer or more flowers. Our results show that flowering phenology may be evolutionarily unstable, possibly a consequence of the deception pollination system. Furthermore, a deception strategy would be relatively unsuccessful in populations where plants are found in either very dense or sparse patches.     

Molecular Cloning, Expression Pattern, and Chromosomal Localization of the Human Na–Cl Thiazide-Sensitive Cotransporter (SLC12A3)

Electrolyte homeostasis is maintained by several ion transport systems. Na–(K)–Cl cotransporters promote the electrically silent movement of chloride across the membrane in absorptive and secretory epithelia. Two kidney-specific Na–(K)–Cl cotransporter isoforms are known, so far, according to their sensitivity to specific inhibitors. We have cloned the human cDNA coding for the renal Na–Cl cotransporter selectively inhibited by the thiazide class of diuretic agents. The predicted protein sequence of 1021 amino acids (112 kDa) shows a structure common to the other members of the Na–(K)–Cl cotransporter family: a central region harboring 12 transmembrane domains and the 2 intracellular hydrophilic amino and carboxyl termini. The ex- pression pattern of the human Na–Cl thiazide-sensitive cotransporter (hTSC, HGMW-approved symbol SLC12A3) confirms the kidney specificity. hTSC has been mapped to human chromosome 16q13 by fluorescencein situhybridization. The cloning and characterization of hTSC now render it possible to study the involvement of this cotransport system in the pathogenesis of tubulopathies such as Gitelman syndrome.     

Characterization of a wilty sunflower (Helianthus annuus L.) mutant II. Water relations, stomatal conductance, abscisic acid content in leaves and xylem sap of plants subjected to water deficiency

The response of w-1, a wilty sunflower (Helianthus annuus L.)mutant, to water stress is described in comparison with thecontrol line (W-1). Detached leaves of w-1 strongly dehydratedduring the first 30 min without significant changes in leafconductance, whereas W-1 responded rapidly to water loss byreducing stomatal aperture. After 2 h stress ABA increased slightlyin w-1, while W-1 leaves showed a 20-fold increase. When waterstress was imposed to potted plants by water withholding, w-1quickly dehydrated, and lost turgor, while W-1 maintained positiveturgor values for a longer period. Wild-type plants respondedto small changes in leaf water potential by accumulating ABAand by closing stomata, whereas in the mutant significant changesin ABA content and in stomatal conductance were found only atvery low water potentials. In another experiment in which waterwas withheld under high relative humidity, when soil water contentstarted to decrease W-1 rapidly closed stomata in the absenceof any change in leaf water status and the reduction in conductancewas paralleled by a rise in xylem sap ABA concentration. Bycontrast the mutant started to accumulate ABA in the xylem sapand to close stomata when soil water content and leaf waterpotential were dramatically reduced. The low endogenous ABAlevels and the inability to synthesize the hormone rapidly eitherin the leaves or in the roots seem to be responsible for thehigh sensitivity of w-1 to water stress. Key words: ABA, Helianthus annuus L, water relations, stomatal conductance, drought, wilty mutant     

Traditional production system of the root of jalapa,Ipomoea purga (convolvulaceae), in Central Veracruz,Mexico

We describe the traditional production system of the root of jalapa, Ipomoea purga, in Xico, Veracruz, Mexico. The results are based on open interviews with the producers to gather information on the development of this crop in the area, and observation of the production system. The production cycle is carried out between July and February. We found that seed scarification is the key to the success of the productive system, obtaining a maximum of 95% seed germination in eight days. This activity, as well as seed collection and the driving of stakes into the ground for plant support, requires a considerable input of man-power. It is an intensive farming process, the cultivated area per farmer varies between 300 m² and 1000 m¹, and the yield ranges between 1.5 and 2.7 tons per hectare of fresh roots; when dried they lose up to 75% of their weight. Smoke-dried roots are exported for sale.     

Gibberellins in suspensor,embryo and integument from very young seeds of Phaseolus coccineus L.

Endogenous gibberellins (GAs) were extracted from suspensor, embryo and integument of very young seeds of Phaseolus coccineus L. and detected by combined gas chromatography-mass spectrometry (GC-MS). Results show the presence of one C₂₀-GA, GA₄₄ and five C₁₉-GAs in the suspensor: GA₁, GA₄, GA₅, GA₆ and GA₈, and four C₁₉-GAs in the integument: GA₁, GA₅, GA₆ and GA₈. Only traces of GA₁ and GA₅ were identified in the embryo. A compound structurally related to GAs was identified as tetrahydroxy-Kauranoic acid in suspensor, integument and, only in trace amounts, in the embryo.     

The role of inorganic phosphate in the regulation of C4 photosynthesis

Inorganic phosphate participates in many fundamental processes within the plant cell. Its broad influence on plant metabolism is related to such key operations as metabolite transport, enzyme regulation and carbohydrate metabolism in general. This review discusses these topics with special emphasis on the role assigned to this ubiquitous anion within the C₄ pathway of photosynthesis.Abbreviations DHAP dihydroxyacetone phosphate - Ga3P glyceraldehyde-3-phosphate - NAD(P)-ME-NAD(P) dependent malic enzyme - PEP phosphoenolpyruvate - 3-PGA 3-phosphoglycerate - PFK and PFP-ATP- and PPi dependent fructose-6-phosphate 1-phosphotransferase - PPDK pyruvate:orthophosphate dikinase - RPPC reductive pentose-phosphate cycle - RuBisCO ribulose bisphosphate carboxylase-oxygenase - SPS sucrose-6-phosphate synthase     

Tissue Fixation for Immunohistochemical Detection of Proliferating Cell Nuclear Antigen with PC10 Monoclonal Antibody

PC10 is a monoclonal antibody to proliferating cell nuclear antigen, a nuclear protein associated with the cell cycle. We have evaluated the effects of tissue fixation on PC10 immunoreactivity in sections of paraffin embedded rat tissues. Immunoreactivity was well preserved in tissues after fixation with alcohol-based solutions for 3-24 hr. Fewer PC10-positive cells were detectable in samples fixed with formaldehydecontaining solutions compared with samples fixed with alcohol for the same time. Loss of PC10 immunoreactivity in formaldehyde fixed tissues was progressive, and quantifiable as early as after 3 hr fixation. Consequently, alcohol-based fixatives are strongly recommended for any immunocytochemical prospective study using PC10 antibody. In contrast, loss of PC10-immunoreactivity is always predictable, but difficult to quantitate, using formaldehyde fixed specimens. This aspect should be considered when using PC10 antibody in retrospective studies with routinely-processed archival material.     

Low Selenium Diet Affects Monoamine Turnover Differentially in Substantia Nigra and Striatum

Abstract: Turnover of dopamine, noradrenaline. serotonin, and their metabolites has been measured in striatum and substantia nigra of adult female rats that were fed control or selenium-deficient diets for 15 days. In addition, the glutathione peroxidase activity has been studied. The most striking result was the increase of dopamine turnover (63%) and 3- methoxytyramine turnover (55%) in substantia nigra between control and experimental animals. On the other hand, no changes were found in the turnover rate of dopamine and its metabolites in the striatum. Likewise, no changes were found in noradrenaline turnover in substantia nigra. In the striatum, there was a significant increase of serotonin turnover versus no change for 5-hydroxy-3-indoleacetic acid. However, in the substantia nigra, serotonin turnover did not show significant changes, whereas 5-hydroxy-3-indoleacetic acid turnover decreased. At the same time, glutathione peroxidase activity significantly decreased in both structures after selenium-deficient diets. These results suggest that a selenium-deficient diet for a short period of time decreases brain protection. principally in the substantia nigra, against oxidative damage.