http://www.bbc.com/news/science-environment-26184116
[Tuna are not air breathing, so the released oil would have to be in the
water column, and not on the surface, in order to have a significant
impact on the tuna. (Due to the subsea location of the Macondo gusher,
some oil would be in the water column as it rose to the surface - for a
fairly short time.)
Dispersants break up up floating oil and allow it to sink - slowly - to
the depths and eventually the sea bottom. Disperants also make the oil
droplets smaller and much more numerous, increasing the potential for
contact and reducing perception of oil presence, thus reducing signals
for fish to avoid the oil hazard in the water.
images, links and podcast in on-line article]
Tuna hearts 'affected by oil spill'
By Jonathan Amos Science correspondent, BBC News, Chicago
14 February 2014
Scientists say that tuna swimming in the Gulf of Mexico during the
Deepwater Horizon oil spill may have experienced heart damage.
Lab research has demonstrated how crude oil chemicals can disrupt heart
function in the fish.
The study, published in Science magazine, is part of the ongoing work to
try to understand the impacts of the disaster.
The gulf is an important spawning ground for bluefin and yellowfin tuna.
Tracking studies have indicated that many of these fish would have been
in the area during the 2010 disaster.
Scientists have long known that certain chemicals in crude oil – such as
polyaromatic hydrocarbons (PAHs) – can be harmful to the hearts of
embryonic and developing fish.
These molecules, which have distinct ring-like structures, cause a
slowing of the heart, irregularities in rhythm and even cardiac arrest
at high exposures.
Pathways blocked
But earlier studies never explained the precise mechanisms involved.
Now, scientists from Stanford University and the National Oceanic and
Atmospheric Administration (Noaa) think they have some answers.
Working on tuna heart tissues in the lab, they have detailed how PAHs
can block important cellular pathways. These are pathways where
potassium and calcium ions move in and out of cells. Their ability to do
so quickly is vital to the proper functioning of those heart cells.
“What we found was that oil blocked key processes in the cardiac cells
involved with linking excitation to contraction, which means that beat
to beat, we slowed the heart cells down and we also decreased their
contractility,” Barbara Block, a professor of marine sciences at
Stanford, told BBC News.
Human implications?
Because the mechanisms involved operate in the same way in the hearts of
all vertebrates, it is highly likely, the team says, that other animals
swimming in waters around the crippled rig would have been exposed to
similar cardiac risks.
And the questions also reach across to human health - because vehicle
engines put PAHs into the air in our cities.
“Impressively, the cardiac excitation-contraction coupling pathways are
the most conserved pathways in all of animals,” said Prof Block.
“It means that the same ion channels present in tuna to make its heart
beat are present in humans.
"So we’re interested in the impact of oil petroleum products on our own
excitation-contraction coupling, and we’re interested in linking air
pollution, for example – a place where petroleum products are often
found, volatiles from our exhausts - to the problems of cardiac
morbidity that are seen across the planet on a very smoggy day.”
Prof Block was explaining her research at the annual meeting of the
American Association for the Advancement of Science (AAAS) in Chicago.
=====================================================================
http://www.sciencedaily.com/releases/2014/02/140213142221.htm
Mechanism of crude oil heart toxicity on fish revealed from oil spill
research
Date:
February 13, 2014
Source:
Stanford University
Summary:
While studying the impact of the 2010 Deepwater Horizon oil spill
on tuna, a research team discovered that crude oil interrupts a
molecular pathway that allows fish heart cells to beat effectively. The
components of the pathway are present in the hearts of most animals,
including humans.
Scientists from Stanford University and the National Oceanic and
Atmospheric Administration (NOAA) have discovered that crude oil
interferes with fish heart cells. The toxic consequence is a slowed
heart rate, reduced cardiac contractility and irregular heartbeats that
can lead to cardiac arrest and sudden cardiac death.
The research, published in the Feb. 14 issue of Science, is part of the
ongoing Natural Resource Damage Assessment of the April 2010 Deepwater
Horizon oil spill.
While crude oil is known to be cardiotoxic to developing fish, the
physiological mechanisms underlying its harmful effects were unclear.
Stanford and NOAA scientists studying the impact of crude oil from the
Deepwater Horizon spill on tuna discovered that it interrupts the
ability of fish heart cells to beat effectively.
Crude oil is a complex mixture of chemicals, some of which are known to
be toxic to marine animals. Past research has focused in particular on
"polycyclic aromatic hydrocarbons" (PAHs), which can also be found in
coal tar, creosote, air pollution and stormwater runoff from land. In
the aftermath of an oil spill, PAHs can persist for many years in marine
habitats and cause a variety of adverse environmental effects.
The researchers report that oil interferes with cardiac cell
excitability, contraction and relaxation -- vital processes for normal
beat-to-beat contraction and pacing of the heart.
Their tests revealed that very low concentrations of crude oil disrupt
the specialized ion channel pores -- where molecules flow in and out of
the heart cells -- that control heart rate and contraction in the
cardiac muscle cell.
This cyclical signaling pathway in cells throughout the heart is what
propels blood out of the pump on every beat. The protein components of
the signaling pathway are highly conserved in the hearts of most
animals, including humans.
The researchers found that oil blocks the potassium channels distributed
in heart cell membranes, increasing the time to restart the heart on
every beat. This prolongs the normal cardiac action potential, and
ultimately slows the heartbeat. The potassium ion channel impacted in
the tuna is responsible for restarting the heart muscle cell contraction
cycle after every beat, and is highly conserved throughout vertebrates,
raising the possibility that animals as diverse as tuna, turtles and
dolphins might be affected similarly by crude oil exposure. Oil also
resulted in arrhythmias in some ventricular cells.
"The ability of a heart cell to beat," explained Barbara Block, a
professor of marine sciences at Stanford, "depends on its capacity to
move essential ions like potassium and calcium into and out of the cells
quickly. This dynamic process, which is common to all vertebrates, is
called 'excitation-contraction coupling.' We have discovered that crude
oil interferes with this vital signaling process essential for our heart
cells to function properly."
"We've known from NOAA research over the past two decades that crude oil
is toxic to the developing hearts of fish embryos and larvae, but
haven't understood precisely why," said coauthor Nat Scholz, leader of
the Ecotoxicology Program at NOAA's Northwest Fisheries Science Center
in Seattle. "These new findings more clearly define petroleum-derived
chemical threats to fish and other species in coastal and ocean
habitats, with implications that extend beyond oil spills to other
sources of pollution such as land-based urban stormwater runoff."
The new study also calls attention to a previously underappreciated risk
to wildlife and humans, particularly from exposure to cardioactive PAHs
that also exist at relatively enriched levels in air pollution.
"When we see these kinds of acute effects at the cardiac cell level,"
Block said, "it is not surprising that chronic exposure to oil from
spills such as the Deepwater Horizon can lead to long-term problems in
fish hearts, as our NOAA colleagues have observed in studies of larval
fish development.
"The protein ion channels we observe in the tuna heart cells are similar
to what we would find in any vertebrate heart and provide evidence as to
how petroleum products may be negatively impacting cardiac function in a
wide variety of animals," she said. "This raises the possibility that
exposure to environmental PAHs in many animals -- including humans --
could lead to cardiac arrhythmias and bradycardia, or slowing of the heart."
The Deepwater Horizon disaster released over 4 million barrels of crude
oil during the peak spawning time for the Atlantic bluefin tuna in the
spring of 2010. Electronic tagging and fisheries catch data indicate
that Atlantic bluefin spawn in the area where the Deepwater Horizon
drilling rig collapsed, raising the possibility that eggs and larvae,
which float near the surface waters, were exposed to oil.
The spill occurred in the major spawning ground of the western Atlantic
population of bluefin tuna in the Gulf of Mexico. The most recent stock
assessment, conducted in 2012, estimated the spawning population to be
at only 36 percent of the 1970 baseline population. Additionally, many
other pelagic fishes were also likely to have spawned in oiled habitats,
including yellowfin tuna, blue marlin and swordfish.
NOAA scientists have previously shown that exposure to crude oil-derived
PAHs disrupts cardiac function and impairs development in larval fishes.
Numerous studies, particularly in the aftermath of the Exxon Valdez
spill in 1989, have described a syndrome of embryonic heart failure,
bradycardia, arrhythmias and edema in exposed fish embryos. The
potential for deleterious effects on young fish in the northern Gulf of
Mexico is still being investigated in the aftermath of the Deepwater
Horizon spill. In the present study, the NOAA team partnered with
Stanford researchers to determine why oil specifically impacts heart cells.
Taking advantage of captive populations of bluefin and yellowfin tuna at
the Tuna Research and Conservation Center (a collaborative facility
operated by Stanford and the Monterey Bay Aquarium), the research team
was able to directly observe the effects of crude oil samples collected
from the Gulf of Mexico on living fish heart cells.
Block and her team bathed isolated cardiac cells from the tuna in low
dose crude oil concentrations similar to what fish in early life stages
may have encountered in the surface waters where they were spawned after
the April 2010 oil spill in the Gulf of Mexico.
They measured the heart cells' response using a combination of
sophisticated electro-physiological techniques -- including "patch
clamping" and "confocal microscopy" -- to record how ions flowed into
and out of the heart cells, and to identify the specific proteins in the
excitation-contraction pathway that were affected by crude oil chemical
components.
"We can examine the function of healthy heart cells in vitro and
actually measure in the microscope how they respond to the presence of
crude oil in real time," said Fabien Brette, a research associate in
Block's lab and lead author on the study.
"The normal sequence and synchronous contraction of the heart requires
rapid activation in a coordinated way of the heart cells," Block said.
"Like detectives, we dissected this process using laboratory
physiological techniques to ask where oil was impacting this vital
mechanism."
Story Source:
The above story is based on materials provided by Stanford University.
Note: Materials may be edited for content and length.
Journal Reference:
Fabien Brette, Ben Machado, Caroline Cros, John P. Incardona,
Nathaniel L. Scholz, Barbara A. Block. Crude Oil Impairs Cardiac
Excitation-Contraction Coupling in Fish. Science, February 14, 2014 DOI:
10.1126/science.1242747
=======================================================================
Paper at: http://www.sciencemag.org/content/343/6172/772
Crude Oil Impairs Cardiac Excitation-Contraction Coupling in Fish
Fabien Brette1, Ben Machado1, Caroline Cros1, John P. Incardona2,
Nathaniel L. Scholz2, Barbara A. Block1,*
Crude oil is known to disrupt cardiac function in fish embryos. Large
oil spills, such as the Deepwater Horizon (DWH) disaster that occurred
in 2010 in the Gulf of Mexico, could severely affect fish at impacted
spawning sites. The physiological mechanisms underlying such potential
cardiotoxic effects remain unclear. Here, we show that crude oil samples
collected from the DWH spill prolonged the action potential of isolated
cardiomyocytes from juvenile bluefin and yellowfin tunas, through the
blocking of the delayed rectifier potassium current (IKr). Crude oil
exposure also decreased calcium current (ICa) and calcium cycling, which
disrupted excitation-contraction coupling in cardiomyocytes. Our
findings demonstrate a cardiotoxic mechanism by which crude oil affects
the regulation of cellular excitability, with implications for
life-threatening arrhythmias in vertebrates.
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