Effects on breathing of focal acidosis at multiple medullary raphe sites in awake goats.

To gain insight into why there are chemoreceptors at widespread sites in the brain, mircrotubules were chronically implanted at two or three sites in the medullary raphe nuclei of adult goats (n = 7). After >2 wk, microdialysis (MD) probes were inserted into the microtubules to create focal acidosis (FA) in the awake state using mock cerebral spinal fluid (mCSF) equilibrated with 6.4% (pH = 7.3), 50% (pH = 6.5), or 80% CO(2) (pH = 6.3), where MD with 50 and 80% CO(2) reduces tissue pH by 0.1 and 0.18 pH unit, respectively. There were no changes in all measured variables with MD with 6.4% at single or multiple raphe sites (P > 0.05). During FA at single raphe sites, only 80% CO(2) elicited physiological changes as inspiratory flow was 16.9% above (P < 0.05) control. However, FA with 50 and 80% CO(2) at multiple sites increased (P < 0.05) inspiratory flow by 18.4 and 30.1%, respectively, where 80% CO(2) also increased (P < 0.05) tidal volume, heart rate, CO(2) production, and O(2) consumption. FA with 80% CO(2) at multiple raphe sites also led to hyperventilation (-2 mmHg), indicating that FA had effects on breathing independent of an increased metabolic rate. We believe these findings suggest that the large ventilatory response to a global respiratory brain acidosis reflects the cumulative effect of stimulation at widespread chemoreceptor sites rather than a large stimulation at a single site. Additionally, focal acidification of raphe chemoreceptors appears to activate an established thermogenic response needed to offset the increased heat loss associated with the CO(2) hyperpnea.     

The effects of ring-size analogs of the antimicrobial peptide gramicidin S on phospholipid bilayer model membranes and on the growth of Acholeplasma laidlawii B.

We have examined the effects of three ring-size analogs of the cyclic beta-sheet antimicrobial peptide gramicidin S (GS) on the thermotropic phase behavior and permeability of phospholipid model membranes and on the growth of the cell wall-less Gram-positive bacteria Acholeplasma laidlawii B. These three analogs have ring sizes of 10 (GS10), 12 (GS12) or 14 (GS14) amino acids, respectively. Our high-sensitivity differential scanning calorimetric studies indicate that all three of these GS analogs perturb the gel/liquid-crystalline phase transition of zwitterionic phosphatidylcholine (PtdCho) vesicles to a greater extent than of zwitterionic phosphatidylethanolamine (PtdEtn) or of anionic phosphatidylglycerol (PtdGro) vesicles, in contrast to GS itself, which interacts more strongly with PtdGro than with PtdCho and PtdEtn bilayers. However, the relative potency of the perturbation of phospholipid phase behavior varies markedly between the three peptides, generally decreasing in the order GS14 > GS10 > GS12. Similarly, these three GS ring-size analogs also differ considerably in their ability to cause fluorescence dye leakage from phospholipid vesicles, with the potency of permeabilization also generally decreasing in the order GS14 > GS10 > GS12. Finally, these GS ring-size analogs also differentially inhibit the growth of A. laidlawii with growth inhibition also decreasing in the order GS14 > GS10 > GS12. These results indicate that the relative potencies of GS and its ring-size analogs in perturbing the organization and increasing the permeability of phospholipid bilayer model membranes, and of inhibiting the growth of A. laidlawii B cells, are at least qualitatively correlated, and provide further support for the hypothesis that the primary target of these antimicrobial peptides is the lipid bilayer of the bacterial membrane. The very high antimicrobial activity of GS14 against the cell wall-less bacteria A. laidlawii as compared to various conventional bacteria confirms our earlier suggestion that the avid binding of this peptide to the bacterial cell wall is primarily responsible for its reduced antimicrobial activity against such organisms. The relative magnitude of the effects of GS itself, and of the three ring-size GS analogs, on phospholipid bilayer organization and cell growth correlate relatively well with the effective hydrophobicities and amphiphilicities of these peptides but less well with their relative charge density, intrinsic hydrophobicities or conformational flexibilities. Nevertheless, all of these parameters, as well as others, may influence the antimicrobial potency and hemolytic activity of GS analogs.     

Human lung density is not altered following normoxic and hypoxic moderate-intensity exercise: implications for transient edema.

The purpose of this study was to examine the effects of exercise on extravascular lung water as it may relate to pulmonary gas exchange. Ten male humans underwent measures of maximal oxygen uptake (Vo2 max) in two conditions: normoxia (N) and normobaric hypoxia of 15% O2 (H). Lung density was measured by quantified MRI before and 48.0 +/- 7.4 and 100.7 +/- 15.1 min following 60 min of cycling exercise in N (intensity = 61.6 +/- 9.5% Vo2 max) and 55.5 +/- 9.8 and 104.3 +/- 9.1 min following 60 min cycling exercise in H (intensity = 65.4 +/- 7.1% hypoxic Vo2 max), where Vo2 max = 65.0 +/- 7.5 ml x kg(-1) x min(-1) (N) and 54.1 +/- 7.0 ml x kg(-1) x min(-1) (H). Two subjects demonstrated mild exercise-induced arterial hypoxemia (EIAH) [minimum arterial oxygen saturation (SaO2 min) = 94.5% and 93.8%], and seven subjects demonstrated moderate EIAH (SaO2 min = 91.4 +/- 1.1%) as measured noninvasively during the Vo2 max test in N. Mean lung densities, measured once preexercise and twice postexercise, were 0.177 +/- 0.019, 0.181 +/- 0.019, and 0.173 +/- 0.019 g/ml (N) and 0.178 +/- 0.021, 0.174 +/- 0.022, and 0.176 +/- 0.019 g/ml (H), respectively. No significant differences (P > 0.05) were found in lung density following exercise in either condition or between conditions. Transient interstitial pulmonary edema did not occur following sustained steady-state cycling exercise in N or H, indicating that transient edema does not result from pulmonary capillary leakage during sustained submaximal exercise.     

The histochemistry of the avian parathyroid and ultimobranchial glands. I. Carbohydrates and proteins

Synopsis The non-enzyme histochemistry of the closely related parathyroid and ultimobranchial glands of the domestic fowl has been studied.The parathyroid cells and the ultimobranchial C cells gave only weakly positive reactions in tests for specific amino-acid residues. The rather stronger reactions found in the C cells were probably related to their content of polypeptide secretory granules. Carbohydrate and lipid stains also gave only negative or weakly positive reactions although the parathyroid cells did contain some free lipid.The lining cells of the ultimobranchial vesicles may be either actively secreting or inactive and cystic. Active cells contain large numbers of granules that are composed of large amounts of sulphated acid mucopolysaccharides, moderate amounts of mucoproteins and small amounts of neutral mucopolysaccharides and glycogen. Both the granular and colloidal secretions of these cells appeared to be identical in composition to the intracellular granules. The vesicular lining cells and their secretions showed strong but variable reactions for sulphydryl, disulphide and amino groups.The intermediate cell strands, which connect the ultimobranchial parathyroid foci with the vesicles, showed a range of reactions intermediate between those exhibited by parathyroid and vesicular cells.The results are discussed in relation to the structure and function of the various cell types.     

Effects of Moisture Deficits on C Translocation in Corn (Zea mays L.)

Corn plants (Zea mays L.) were grown in the field on two soils. On a droughty soil, water was withheld from some plants during the grain-filling period while other plants were irrigated. Carbon-14 was fed to the leaves, and translocation to different plant parts was determined. Translocation appeared to be more sensitive to moisture stress than was photosynthesis. More radioactive carbon was retained in both the fed portion and the nonfed portion of the leaf of stressed plants than in nonstressed plants. The stalk segment between the treated leaf and ear-node also contained less radioactivity in stressed plants than in nonstressed plants. On a soil with higher water-holding capacity, moisture stress was imposed on plants by root pruning. Plants under severe stress continued to translocate photosynthetically assimilated ¹⁴C nearly as well as nonstressed plants for 90 minutes. Between 90 and 120 minutes after labeling, there was a major reduction in amount translocated in stressed plants compared to the nonstressed plants. At longer translocation times the rates of translocation appeared again to be more nearly equal.     

Enzyme cytochemical observations on the tissue stages of the life cycle of Eimeria acervulina and Eimeria necatrix

Cytochemical studies concerning the presence and distribution of various enzymes in the tissue stages of the life cycle of Eimeria acervulina and E. necatrix have been undertaken.Acid and alkaline phosphatases as well as ATPase (pH 7·2) were found to be present in all the stages of the life cycles examined, the latter enzyme being very strong in the plastic granules of the macrogametocytes and in the inner membrane of the oocyst wall. The reaction for all three enzymes was observed in the cytoplasm but not the nucleus. Non-specific esterase and glucose-6-phosphatase were also found in all stages examined, the latter occurring in greater amounts in stages where deposition of glycogen (amylopectin) was pronounced. Succinic dehydrogenase occurred only in the second generation schizonts and merozoites of E. necatrix and in the formed oocysts of both species. No reaction for β-glucuronidase or leucine naphthylamidase was apparent in any stage, although a slight reaction for leucine naphthlyamidase was seen in the second generation merozoites of E. necatrix lying free in the intestinal lumen.The presence and distribution of these enzymes and their possible function were discussed.     

Characterization of Plasma Membrane-associated Adenosine Triphosphase Activity of Oat Roots

ATPase activity of plasma membranes isolated from oat (Avena sativa L. cv. Goodfield) roots was activated by divalent cations (Mg²⁺ = Mn²⁺ > Zn²⁺ > Fe²⁺ > Ca²⁺) and further stimulated by KCl and a variety of monovalent salts, both inorganic and organic. The enzyme exhibited greater specificity for cations than anions. The presence of Mg²⁺ was necessary for KCl stimulation. Ca²⁺ was ineffective in replacing Mg²⁺ for activation of plasma membrane ATPase, but it did activate other membrane-bound ATPases. The pH optima for Mg²⁺ activation and KCl stimulation of the plasma membrane ATPase were 7.5 and 6.5, respectively.