A 31P-NMR study of some metabolic and functional effects of the inotropic agents epinephrine and ouabain,and the ionophore R02-2985 (X537A) in the isolated,perfused rat heart

1. Some metabolic effects of increased mechanical activity by the Langendorff-perfused rat heart have been characterized using ³¹P-NMR. Mechanical activity was increased by infusion of ouabain (0.9?7.0·10^?5 M), the ionophore R02-2985 (1·10^?5 M) or epinephrine (5·10^?8 M). 2. Similar metabolic changes accompanied infusion of each of the positive inotropic agents into hearts perfused with buffer containing 11 mM glucose as the substrate. In each case phosphocreatine concentrations decreased. During the period of epinephrine infusion the phosphocreatine began to recover its original concentration, although there were no significant changes in mechanical activity. 3. Comparisons of the metabolic changes accompanying the positive inotropic and chronotropic effects of epinephrine were made between hearts perfused with either glucose (11 mM), acetate (5 mM) or lactate (5 mM). A time-dependent decrease in phosphocreatine concentrations also accompanied infusion of epinephrine into hearts perfused with lactate as the sole exogenous substrate, but no statistically significant metabolite changes were observed after identical epinephrine infusions with acetate as the substrate. 4. Calculation of the concentration of free ADP assuming equilibrium in the creatine phosphokinase reaction allows estimation of the cytosolic phosphate potential ($\text{[}\text{ATP}\text{]}\text{[ADP][P}{}_{\mathrm{<mtext>i</mtext>}}\text{]}$), which appears to be dependent on a number of factors, including the nature of the exogenous substrate and the level of mechanical activity. 5. Thus, we conclude that there is no general correlation between the phosphate potential and the mitochondrial respiratory rate in the perfused rat heart.     

Sequence Similarity in Nuclear and Mitochondrial Gene Regions in Plants

A 114-basepair fragment at 5′-upstream of the gene oee2-A from Nicotiana tabacum encoding the 23kD polypeptide of oxygen-evolving complex of photosystem II was found, through database search, to have high sequence similarity with segments in the mitochondrial genome of Oenothera, watermelon and wheat. This observation is supported by the Southern hybridization data. Repeated sequences were also found in the nuclear-mitochondrial homologous region, However, the function of these repeats is yet to be determined.     

Chemical properties and NMR spectroscopic identification of certain fungal siderophores

Siderophores of six fungi viz. Aspergillus sp. ABp4, Aureobacidium pullulans, Penicillium oxalicum, P. chrysosporium, Mycotypha africana and Syncephalastrum racemosum were examined for their (1) electrophoretic mobilities to determine the acidic, basic or neutral charge; (2) Fe (III) binding nature viz., mono-, di-, or trihydroxamate; (3) amino acid composition; and (4) NMR (nuclear magnetic resonance) spectroscopy to determine their structure. Electrophoretic mobilities of siderophores of 3 fungi (P. oxalicum, P. chrysosporium, and M, africana) exhibited net basic charge, siderophores of 2 fungi (Aspergillus sp. ABp4 and S. racemosum) were acidic and 1 fungus (A. pullullans) was neutral. Electrophoresis of ferrated siderophore at pH 2 and colour of the spots indicated that siderophores of Aspergillus sp. ABp4 and P. oxalicum and A. pullulans were trihydroxamates, whereas siderophore of P. chrysosporium was dihydroxamate. Amino acid composition of siderophores purified by XAD-2 column chromatography, revealed the presence of asparagine, histidine, and proline in Aspergillus sp. ABp4, serine and alanine in P. chrysosporium, and valine in M. africana. The structure of purified siderophores as revealed by NMR spectroscopy identified siderophore of AB - 2670 (A. pullulans) as asperchrome F1, and AB-513 (M. africana) as rhizoferrin. The peak obtained for siderophore AB-5 (Aspergillus sp. ABp4) did not show resemblance to any known siderophore, therefore may be an exception.     

Calcium transport by isolated anterior and posterior Malpighian tubules of Drosophila melanogaster: roles of sequestration and secretion

Ca(2+) transport was examined in isolated Malpighian tubules (MTs) of adult Drosophila melanogaster. All segments of both anterior and posterior MTs have substantial capacity to transport Ca(2+) and to play a role, therefore, in calcium homeostasis and elimination of excess dietary Ca(2+). Approximately 85% of Ca(2+) which enters the tubule is sequestered, and approximately 15% is secreted in soluble form into the tubule lumen. Tubules secreting fluid at maximal rates can remove an amount of Ca(2+) equal to the whole animal calcium content in approximately 9 h. Distal segments of the pair of anterior MTs can sequester the same amount of Ca(2+) in <2 h. Functional advantages of high Ca(2+) turnover rates are discussed. Transepithelial Ca(2+) secretion is increased by treatments which depolarize the transepithelial potential (thapsigargin, high K(+)), or acidify the secreted fluids (bicarbonate-free salines). The effects of pharmacological reagents and variations in bathing saline ionic composition indicate that the processes of secretion and sequestration are controlled independently, and that diltiazem-sensitive Ca(2+) channels are an important component of sequestration. The contribution of some form of apical Ca(2+) pump is evaluated.     

Helium-neon laser preirradiation induces protection against UVC radiation in wild-type E. coli strain K12AB1157

We have observed that preirradiation with a helium-neon laser (632.8 nm) induces protection against UVC radiation in wild-type E. coli strain K12AB1157. The magnitude of protection was found to depend on the helium-neon laser irradiance, exposure time, and period of incubation between helium-neon laser exposure and subsequent UVC irradiation. The optimum values for dose, irradiance and interval between the two exposures were found to be 7 kJ/m(2), 100 W/m(2) and 1 h, respectively. The possible involvement of singlet oxygen in the helium-neon laser-induced protection is also discussed.     

Differences in growth and water relations among Phaseolus vulgaris cultivars in response to induced drought stress

Relatively little ecophysiological research has been conducted to determine the responses to drought of Phaseolus vulgaris. Four bean cultivars (cvs.) from Brazil, A320, Carioca, Ouro Negro and Xodó were submitted to an imposed water deficit in order to evaluate the importance of some adaptive mechanisms of drought resistance through the analysis of growth parameters, water status, gas exchange and indicators of tolerance mechanisms at the cellular level. During the drought treatment, relative growth rates were more reduced for A320 and Xodó than Carioca and Ouro Negro. A320 closed its stomata very rapidly and complete stomatal closure was obtained at Psi(w)=-0.6 MPa, in contrast to the other cvs. where stomata were fully closed only at Psi(w)=-0.9 MPa. Net assimilation rates were closely related to stomatal conductances. Mechanisms at the cellular level appeared to be mostly important for higher tolerance. Carioca and Ouro Negro, when compared to A320 and Xodó, were characterized by having better drought tolerance mechanisms and higher tissue water retention capacity leading to a better growth under water deficits. The leaf dehydration rates of those cvs. were slow whereas those of the drought sensitive cvs. were rapid. The results were confirmed by the electrolyte leakage test and leaf osmotic potential measurements, which indicated higher membrane resistance and osmotic adjustment in the two tolerant cvs. Carioca and Ouro Negro. It appears from this study that despite being cultivated in the same geographical region, the four cvs. of P. vulgaris displayed somewhat different drought adaptive capacities for prolonged drought during the vegetative phase.     

Evidence of NPY Y5 receptor involvement in food intake elicited by orexin A in sated rats

Intracerebroventricular (icv) injections of orexin A stimulate feeding in sated rats. Since neuropeptide Y is a potent orexigenic peptide and orexin-containing neurons are morphologically linked with NPY-producing neurons in the hypothalamus, we evaluated the functional relationship between the two orexigenic peptides. The results show that whereas it was ineffective on its own, a selective NPY Y5 receptor antagonist, injected icv 15 min. before orexin A significantly suppressed orexin A-induced feeding. Since previous investigations demonstrated that an NPY Y1 receptor antagonist also inhibits feeding induced by orexin A, the current results further underscore the existence of a functional link between orexin and NPY producing neurons as the orexin network appears to be capable of influencing NPYergic signaling through Y1 and Y5 receptors to stimulate feeding.     

Single crystals and oriented crystallization of ivory nut mannan

The preparation of lamellar single crystals of mannan[poly((1 → 4)-β-D-mannose)] is described. Electron diffractograms clearly identify the perpendicular orientation of the chain axis with respect to the lamellar surface. Since the degree of polymerization is 40 or less, no conclusion is made as to chain folding. The unit cell corresponds to the mannan I structure derived from x-ray fiber data on oriented algal mannan. The baseplane dimensions found were a = 7.22 Å and b = 8.92 Å, and the systematic absences observed confirm the proposed P2₁2₁2₁ group. It was found that cellulose microfibrils from Valonia ventricosa and bacterial cellulose could serve as extended chain nuclei for inducing oriented crystallization of mannan on cellulose. This produces a shish-kebab type of morphology.     

Shear stress-induced vasodilation in porcine coronary conduit arteries is independent of nitric oxide release

The present study was performed to determine the importance of nitric oxide in eliciting epicardial coronary artery dilation during sustained increases in shear stress in the absence of pulsatile flow. Isolated first-order porcine epicardial coronary conduit arteries (approximately 500 microm) were preconstricted (U-46619) and subjected to steady-state changes in flow in vitro. Nonpulsatile flow (shear stress range from 0 to approximately 100 dyn/cm2) produced a graded dilation of epicardial arteries. Inhibiting nitric oxide synthase with 10(-5) M N(omega)-nitro-L-arginine methyl ester (L-NAME) blocked bradykinin-induced vasodilation but did not affect the flow-diameter relation or the maximum change in diameter from static conditions (67 +/- 10 microm in control vs. 71 +/- 8 microm after L-NAME, P = not significant). The addition of indomethacin (10(-5) M) had no effect on flow-mediated vasodilation. Depolarizing vascular smooth muscle with KCl (60 mM) or removing the endothelium blocked bradykinin vasodilation and completely abolished flow-mediated responses. The K+ channel blocker tetraethylammonium chloride (TEA; 10(-4)M) attenuated flow-mediated vasodilation (maximum diameter change was 110 +/- 18 microm under control conditions vs. 58 +/- 10 microm after TEA, P < 0.001). These data indicate that epicardial coronary arteries dilate to steady-state changes in nonpulsatile flow via a mechanism that is independent of nitric oxide production. The ability to completely block this with KCl and attenuate it with TEA supports the hypothesis that epicardial coronary arteries dilate to steady levels of shear stress through hyperpolarization of vascular smooth muscle. This may be secondary to the release of an endothelium-dependent hyperpolarizing factor.