Role of small conductance calcium-activated potassium channels expressed in PVN in regulating sympathetic nerve activity and arterial blood pressure in rats

Small conductance Ca(2+)-activated K(+) (SK) channels regulate membrane properties of rostral ventrolateral medulla (RVLM) projecting hypothalamic paraventricular nucleus (PVN) neurons and inhibition of SK channels increases in vitro excitability. Here, we determined in vivo the role of PVN SK channels in regulating sympathetic nerve activity (SNA) and mean arterial pressure (MAP). In anesthetized rats, bilateral PVN microinjection of SK channel blocker with peptide apamin (0, 0.125, 1.25, 3.75, 12.5, and 25 pmol) increased splanchnic SNA (SSNA), renal SNA (RSNA), MAP, and heart rate (HR) in a dose-dependent manner. Maximum increases in SSNA, RSNA, MAP, and HR elicited by apamin (12.5 pmol, n = 7) were 330 ± 40% (P < 0.01), 271 ± 40% (P < 0.01), 29 ± 4 mmHg (P < 0.01), and 34 ± 9 beats/min (P < 0.01), respectively. PVN injection of the nonpeptide SK channel blocker UCL1684 (250 pmol, n = 7) significantly increased SSNA (P < 0.05), RSNA (P < 0.05), MAP (P < 0.05), and HR (P < 0.05). Neither apamin injected outside the PVN (12.5 pmol, n = 6) nor peripheral administration of the same dose of apamin (12.5 pmol, n = 5) evoked any significant changes in the recorded variables. PVN-injected SK channel enhancer 5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one (DCEBIO, 5 nmol, n = 4) or N-cyclohexyl-N-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-4-pyrimidin]amine (CyPPA, 5 nmol, n = 6) did not significantly alter the SSNA, RSNA, MAP, and HR. Western blot and RT-PCR analysis of punched PVN tissue showed abundant expression of SK1-3 channels. We conclude that SK channels expressed in the PVN play an important role in the regulation of sympathetic outflow and cardiovascular function.     

Turnover of myosin heavy and light chains in cultured embryonic chick cardiac and skeletal muscle

The relative rates of synthesis and breakdown of myosin heavy and light chains were studied in primary cell cultures of embryonic chick cardiac and skeletal muscle. Measurements were made after 4 days in culture, at which time both skeletal and cardiac cultures were differentiated and contracted spontaneously. Following a 4-hr pulse of radioactive leucine, myosin and its heavy and light chains were extracted to 90% or greater purity and the specific activities of the proteins were determined. In cardiac muscle, myosin heavy chains were synthesized approximately 1.6 times the rate of myosin light chains, and in skeletal muscle, heavy chains were synthesized at approximately 1.4 times the rate of light chains. Relative rates of degradation of muscle proteins were determined using a dual-isotope technique. In general, the soluble and myofibrillar proteins of both types of muscle had decay rates proportional to their molecular weights (larger proteins generally had higher decay rates) based on analyses utilizing sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A notable exception to this general rule was myosin heavy chains, which had decay rates only slightly higher than the myosin light chains. Direct measurements on purified proteins indicated that the heavy chains of myosin were turning over at a slightly greater rate (approximately 20%) than the myosin light chains in both cardiac and skeletal muscle. The reasons for the apparent discrepancy between these measurements of myosin heavy and light chain synthesis and degradation are discussed.     

Conservation significantly improves wetland conditions: evaluation of playa wetlands in different conservation status

This study assessed the conditions of wetland hydrology, hydrophyte and soil under different state and federal conservation programs, and then identified the restorable potential of conserved playas. The distribution of hydrology and hydrophyte were geospatially examined through annual tracking the quantity and quality of wetlands on historical hydric soil footprints under different conservation programs in the Rainwater Basin in Nebraska, USA during 2004–2015. The results show that the historical hydric soil footprints with the conservation programs had significantly better performance in ponded water and hydrophyte than non-conserved wetlands. The yearly average of ponded water areas within footprints varies at 12.59% for the Waterfowl Production Areas (WPAs), 14.78% for Wildlife Management Areas (WMAs), 27.37% for Wetlands Reserve Program’s conservation easements (WRPs), and 1.86% for non-conserved wetlands, respectively. The yearly average of hydrophyte plant community coverage within footprints reaches at 77.51% for WPAs, 79.28% for WMAs, and 66.53% for WRPs, and 8.82% for non-conserved hydric footprints. Within conserved lands, Massie/Water soil series demonstrated the prominent ability to hold ponding water, especially in the ponded footprints with higher ponding frequency. Nevertheless, the proportion of Fillmore, Rusco or Butler soil series roughly decreased when the ponding water frequency increased. The areas, with high likelihood to be restored, are the places between annual ponding/hydrophyte covered areas and 11 years’ maximized ponding/hydrophyte areas.

     

Co-Infection by Chytrid Fungus and Ranaviruses in Wild and Harvested Frogs in the Tropical Andes

While global amphibian declines are associated with the spread of Batrachochytrium dendrobatidis (Bd), undetected concurrent co-infection by other pathogens may be little recognized threats to amphibians. Emerging viruses in the genus Ranavirus (Rv) also cause die-offs of amphibians and other ectotherms, but the extent of their distribution globally, or how co-infections with Bd impact amphibians are poorly understood. We provide the first report of Bd and Rv co-infection in South America, and the first report of Rv infections in the amphibian biodiversity hotspot of the Peruvian Andes, where Bd is associated with extinctions. Using these data, we tested the hypothesis that Bd or Rv parasites facilitate co-infection, as assessed by parasite abundance or infection intensity within individual adult frogs. Co-infection occurred in 30% of stream-dwelling frogs; 65% were infected by Bd and 40% by Rv. Among terrestrial, direct-developing Pristimantis frogs 40% were infected by Bd, 35% by Rv, and 20% co-infected. In Telmatobius frogs harvested for the live-trade 49% were co-infected, 92% were infected by Bd, and 53% by Rv. Median Bd and Rv loads were similar in both wild (Bd = 10^1.2 Ze, Rv = 10^2.3 viral copies) and harvested frogs (Bd = 10^3.1 Ze, Rv = 10^2.7 viral copies). While neither parasite abundance nor infection intensity were associated with co-infection patterns in adults, these data did not include the most susceptible larval and metamorphic life stages. These findings suggest Rv distribution is global and that co-infection among these parasites may be common. These results raise conservation concerns, but greater testing is necessary to determine if parasite interactions increase amphibian vulnerability to secondary infections across differing life stages, and constitute a previously undetected threat to declining populations. Greater surveillance of parasite interactions may increase our capacity to contain and mitigate the impacts of these and other wildlife diseases.     

Chronic angiotensin II infusion attenuates the renal sympathoinhibitory response to acute volume expansion

In this study the hypothesis was tested that chronic infusion of ANG II attenuates acute volume expansion (VE)-induced inhibition of renal sympathetic nerve activity (SNA). Rats received intravenous infusion of either vehicle or ANG II (12 ng. kg(-1). min(-1)) for 7 days. ANG II-infused animals displayed an increased contribution of SNA to the maintenance of mean arterial pressure (MAP) as indicated by ganglionic blockade, which produced a significantly (P < 0.01) greater decrease in MAP (75 +/- 3 mmHg) than was observed in vehicle-infused (47 +/- 8 mmHg) controls. Rats were then anesthetized, and changes in MAP, mean right atrial pressure (MRAP), heart rate (HR), and renal SNA were recorded in response to right atrial infusion of isotonic saline (20% estimated blood volume in 5 min). Baseline MAP, HR, and hematocrit were not different between groups. Likewise, MAP was unchanged by acute VE in vehicle-infused animals, whereas VE induced a significant bradycardia (P < 0.05) and increase in MRAP (P < 0.05). MAP, MRAP, and HR responses to VE were not statistically different between animals infused with vehicle vs. ANG II. In contrast, VE significantly (P < 0.001) reduced renal SNA by 33.5 +/- 8% in vehicle-infused animals but was without effect on renal SNA in those infused chronically with ANG II. Acutely administered losartan (3 mg/kg iv) restored VE-induced inhibition of renal SNA (P < 0.001) in rats chronically infused with ANG II. In contrast, this treatment had no effect in the vehicle-infused group. Therefore, it appears that chronic infusion of ANG II can attenuate VE-induced renal sympathoinhibition through a mechanism requiring AT(1) receptor activation. The attenuated sympathoinhibitory response to VE in ANG II-infused animals remained after arterial barodenervation and systemic vasopressin V(1) receptor antagonism and appeared to depend on ANG II being chronically increased because ANG II given acutely had no effect on VE-induced renal sympathoinhibition.     

Serum- and glucocorticoid-regulated kinase 1 regulates ubiquitin ligase neural precursor cell-expressed, developmentally down-regulated protein 4-2 by inducing interaction with 14-3-3

Serum- and glucocorticoid-regulated kinase 1 (SGK1) is an aldosterone-regulated early response gene product that regulates the activity of several ion transport proteins, most notably that of the epithelial sodium channel (ENaC). Recent evidence has established that SGK1 phosphorylates and inhibits Nedd4-2 (neural precursor cell-expressed, developmentally down-regulated protein 4-2), a ubiquitin ligase that decreases cell surface expression of the channel and possibly stimulates its degradation. The mechanistic basis for this SGK1-induced Nedd4-2 inhibition is currently unknown. In this study we show that SGK1-mediated phosphorylation of Nedd4-2 induces its interaction with members of the 14-3-3 family of regulatory proteins. Through functional characterization of Nedd4-2-mutant proteins, we demonstrate that this interaction is required for SGK1-mediated inhibition of Nedd4-2. The concerted action of SGK1 and 14-3-3 appears to disrupt Nedd4-2-mediated ubiquitination of ENaC, thus providing a mechanism by which SGK1 modulates the ENaC-mediated Na(+) current. Finally, the expression pattern of 14-3-3 is also consistent with a functional role in distal nephron Na(+) transport. These results demonstrate a novel, physiologically significant role for 14-3-3 proteins in modulating ubiquitin ligase-dependent pathways in the control of epithelial ion transport.     

Effect of elevated FFA on carbohydrate and lipid oxidation during prolonged exercise in humans

Increased availability of circulating free fatty acids (FFA) inhibits the rate of glycolysis in heart and resting skeletal muscle (Randle effect). Whether elevated FFA may play a role in decreasing carbohydrate oxidation during prolonged exercise in humans is more controversial. Using respiratory exchange measurements, we measured substrate utilization during 2.5 h of exercise at approximately 44 +/- 1% maximal O2 uptake (VO2 max) in the presence or absence of elevated FFA levels. After 30 min of base-line determinations, 1,000 U heparin was given intravenously and a 3-h constant infusion of Intralipid 10% (150 g/h) and heparin (500 U/h) was started. After an additional 30 min of rest, subjects exercised for 2.5 h (study 1, n = 6). In another five subjects (study 2) 100 g glucose was ingested after 30 min of exercise. The same protocols (studies 1 and 2) were also performed during a 0.9%-saline infusion. During exercise, without glucose ingestion, higher FFA concentrations prevailed during the Intralipid infusion (1,122 +/- 40 vs. 782 +/- 65 mumol/l), but the relative contributions of carbohydrate (49 +/- 4 vs. 50 +/- 4%) or lipid (49 +/- 4 vs. 47 +/- 6%) oxidation to the total energy expenditure were different only during the first 30 min of exercise. Similarly, higher FFA levels (1,032 +/- 62 vs. 568 +/- 46 mumol/l) did not alter the relative contributions of carbohydrate (62 +/- 4 vs. 69 +/- 2%) or lipid (36 +/- 4 vs. 29 +/- 2%) oxidation to the total energy expenditure after glucose feeding.(ABSTRACT TRUNCATED AT 250 WORDS)     

Listeria monocytogenes infection in Biozzi mouse lines with high or low antibody responses, or with high (Hi/PHA) or low (Lo/PHA) responses to phytohemagglutinin

Dependent and independent variables influencing natural and acquired resistance to Listeria monocytogenes in Biozzi mouse lines, genetically selected for their antibody responses, were analyzed. Variations in interline (IL) difference were shown to depend upon the inoculum dose, age, and sex of the mice used. Further, when IL differences were measured using the growth curves of L. monocytogenes, it appeared that LL mice were more resistant than HL mice, while the opposite was observed when IL differences were appreciated using the mortality rate. Attempts to analyze such apparently contradictory results showed that the predominant mechanism in LL mice was a higher natural bactericidal capacity of resident macrophages, which might be compensated for in HL mice by a higher ability to recruit blood-borne monocytes during the secondary, nonspecific phase of resistance, being reinforced and associated with a higher DTH reaction to L. monocytogenes antigen. A similar, higher antilisterial resistance was also observed in other Biozzi lines, genetically selected for their high in vitro CMI response to PHA as compared with the Lo/PHA line.