178 research outputs found
Long‐term dietary shift and population decline of a pelagic seabird — A health check on the tropical Atlantic?
The response of the tandem pore potassium channel TASK-3 (K2P9.1) to voltage : gating at the cytoplasmic mouth
Although the tandem pore potassium channel TASK-3 is thought to open and shut at its
selectivity filter in response to changes of extracellular pH, it is currently unknown whether the
channel also shows gating at its inner, cytoplasmic mouth through movements of membrane
helices M2 and M4.We used two electrode voltage clamp and single channel recording to show
that TASK-3 responds to voltage in a way that reveals such gating. In wild-type channels, Popen
was very low at negative voltages, but increased with depolarisation. The effect of voltage was
relatively weak and the gating charge small, ∼0.17.Mutants A237T (in M4) and N133A (in M2)
increased Popen at a given voltage, increasing mean open time and the number of openings per
burst. In addition, the relationship between Popen andvoltagewas shifted to lesspositive voltages.
Mutation of putative hinge glycines (G117A, G231A), residues that are conserved throughout
the tandem pore channel family, reduced Popen at a given voltage, shifting the relationship
with voltage to a more positive potential range. None of these mutants substantially affected
the response of the channel to extracellular acidification. We have used the results from single
channel recording to develop a simple kinetic model to show how gating occurs through two
classes of conformation change, with two routes out of the open state, as expected if gating
occurs both at the selectivity filter and at its cytoplasmic mouth
The selectivity, voltage-dependence and acid sensitivity of the tandem pore potassium channel TASK-1 : contributions of the pore domains
We have investigated the contribution to ionic
selectivity of residues in the selectivity filter and pore
helices of the P1 and P2 domains in the acid sensitive
potassium channel TASK-1. We used site directed mutagenesis
and electrophysiological studies, assisted by structural
models built through computational methods. We have
measured selectivity in channels expressed in Xenopus
oocytes, using voltage clamp to measure shifts in reversal
potential and current amplitudes when Rb+ or Na+ replaced
extracellular K+. Both P1 and P2 contribute to selectivity,
and most mutations, including mutation of residues in the
triplets GYG and GFG in P1 and P2, made channels nonselective.
We interpret the effects of these—and of other
mutations—in terms of the way the pore is likely to be
stabilised structurally. We show also that residues in the
outer pore mouth contribute to selectivity in TASK-1.
Mutations resulting in loss of selectivity (e.g. I94S, G95A)
were associated with slowing of the response of channels to
depolarisation. More important physiologically, pH sensitivity
is also lost or altered by such mutations. Mutations
that retained selectivity (e.g. I94L, I94V) also retained their
response to acidification. It is likely that responses both to
voltage and pH changes involve gating at the selectivity filter
The stress hormone corticosterone in a marine top predatorreflects short-term changes in food availability
-In many seabird studies, single annual proxies of prey abundance have been
used to explain variability in breeding performance, but much more important
is probably the timing of prey availability relative to the breeding season when
energy demand is at a maximum. Until now, intraseasonal variation in prey
availability has been difficult to quantify in seabirds. Using a state-of-the-art
ocean drift model of larval cod Gadus morhua, an important constituent of the
diet of common guillemots Uria aalge in the southwestern Barents Sea, we were
able to show clear, short-term correlations between food availability and measurements
of the stress hormone corticosterone (CORT) in parental guillemots
over a 3-year period (2009–2011). The model allowed the extraction of abundance
and size of cod larvae with very high spatial (4 km) and temporal resolutions
(1 day) and showed that cod larvae from adjacent northern spawning
grounds in Norway were always available near the guillemot breeding colony
while those from more distant southerly spawning grounds were less frequent,
but larger. The latter arrived in waves whose magnitude and timing, and thus
overlap with the guillemot breeding season, varied between years. CORT levels
in adult guillemots were lower in birds caught after a week with high frequencies
of southern cod larvae. This pattern was restricted to the two years (2009
and 2010) in which southern larvae arrived before the end of the guillemot
breeding season. Any such pattern was masked in 2011 by already exceptionally
high numbers of cod larvae in the region throughout chick-rearing period. The
findings suggest that CORT levels in breeding birds increase when the arrival of
southern sizable larvae does not match the period of peak energy requirements
during breeding.
Common guillemot, CORT, food availability,
seabird, Uria aalg
A Quantitative Analysis of Flight Feather Replacement in the Moustached Tree Swift Hemiprocne mystacea, a Tropical Aerial Forager
The functional life span of feathers is always much less than the potential life span of birds, so feathers must be renewed regularly. But feather renewal entails important energetic, time and performance costs that must be integrated into the annual cycle. Across species the time required to replace flight feather increases disproportionately with body size, resulting in complex, multiple waves of feather replacement in the primaries of many large birds. We describe the rules of flight feather replacement for Hemiprocne mystacea, a small, 60g tree swift from the New Guinea region. This species breeds and molts in all months of the year, and flight feather molt occurs during breeding in some individuals. H. mystacea is one to be the smallest species for which stepwise replacement of the primaries and secondaries has been documented; yet, primary replacement is extremely slow in this aerial forager, requiring more than 300 days if molt is not interrupted. We used growth bands to show that primaries grow at an average rate of 2.86 mm/d. The 10 primaries are a single molt series, while the 11 secondaries and five rectrices are each broken into two molt series. In large birds stepwise replacement of the primaries serves to increase the rate of primary replacement while minimizing gaps in the wing. But stepwise replacement of the wing quills in H. mystacea proceeds so slowly that it may be a consequence of the ontogeny of stepwise molting, rather than an adaptation, because the average number of growing primaries is probably lower than 1.14 feathers per wing
The pore structure and gating mechanism of K2P channels
K2P potassium channels are important regulators of cellular excitability. This study reveals that in contrast to most other K+ channels the primary gating mechanism in the K2P channel TREK-1 does not involve opening and closure of the cytoplasmic bundle crossing, but takes place close to or within the selectivity filter
Can Thermoclines Be a Cue to Prey Distribution for Marine Top Predators? A Case Study with Little Penguins
The use of top predators as bio-platforms is a modern approach to understanding how physical changes in the environment may influence their foraging success. This study examined if the presence of thermoclines could be a reliable signal of resource availability for a marine top predator, the little penguin (Eudyptula minor). We studied weekly foraging activity of 43 breeding individual penguins equipped with accelerometers. These loggers also recorded water temperature, which we used to detect changes in thermal characteristics of their foraging zone over 5 weeks during the penguin’s guard phase. Data showed the thermocline was detected in the first 3 weeks of the study, which coincided with higher foraging efficiency. When a thermocline was not detected in the last two weeks, foraging efficiency decreased as well. We suggest that thermoclines can represent temporary markers of enhanced food availability for this top-predator to which they must optimally adjust their breeding cycle
Migratory Pathways and Connectivity in Asian Houbara Bustards: Evidence from 15 Years of Satellite Tracking
Information on migratory pathways and connectivity is essential to understanding population dynamics and structure of migrant species. Our manuscript uses a unique dataset, the fruit of 103 individual Asian houbara bustards captured on their breeding grounds in Central Asia over 15 years and equipped with satellite transmitters, to provide a better understanding of migratory pathways and connectivity; such information is critical to the implementation of biologically sound conservation measures in migrant species. At the scale of the distribution range we find substantial migratory connectivity, with a clear separation of migration pathways and wintering areas between western and eastern migrants. Within eastern migrants, we also describe a pattern of segregation on the wintering grounds. But at the local level connectivity is weak: birds breeding within the limits of our study areas were often found several hundreds of kilometres apart during winter. Although houbara wintering in Arabia are known to originate from Central Asia, out of all the birds captured and tracked here not one wintered on the Arabian Peninsula. This is very likely the result of decades of unregulated off-take and severe habitat degradation in this area. At a time when conservation measures are being implemented to safeguard the long-term future of this species, this study provides critical data on the spatial structuring of populations
Orai/CRACM1 and KCa3.1 ion channels interact
open access articleBACKGROUND:
Orai/CRACM1 ion channels provide the major Ca(2+) influx pathway for FcεRI-dependent human lung mast cell (HLMC) mediator release. The Ca(2+)-activated K(+) channel KCa3.1 modulates Ca(2+) influx and the secretory response through hyperpolarisation of the plasma membrane. We hypothesised that there is a close functional and spatiotemporal interaction between these Ca(2+)- and K(+)-selective channels.
RESULTS:
Activation of FcεRI-dependent HLMC KCa3.1 currents was dependent on the presence of extracellular Ca(2+), and attenuated in the presence of the selective Orai blocker GSK-7975A. Currents elicited by the KCa3.1 opener 1-EBIO were also attenuated by GSK-7975A. The Orai1 E106Q dominant-negative mutant ablated 1-EBIO and FcεRI-dependent KCa3.1 currents in HLMCs. Orai1 but not Orai2 was shown to co-immunoprecipitate with KCa3.1 when overexpressed in HEK293 cells, and Orai1 and KCa3.1 were seen to co-localise in the HEK293 plasma membrane using confocal microscopy.
CONCLUSION:
KCa3.1 activation in HLMCs is highly dependent on Ca(2+) influx through Orai1 channels, mediated via a close spatiotemporal interaction between the two channels
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