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| Angelika
Lüdtke |
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Home
Institution
Eberhard-Karls-Universitaet Tuebingen
Host
Institution
NIH / NIDDK / MDB, Laboratory for Renal Function and Development, Bethesda,
Maryland
Mentors: Jurgen Schnermann, M.D.; Josie Briggs, MD
E-Mail
angelika_luedtke@gmx.de
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Research
Topic
see Abstract |
Personal
Reactions to the U.S. Experience
This short time here was packed with horrible and frightening things (especially
in DC), but also with new, exciting and very interesting experiences. It
will probably take a while to mentally digest all this. The NIH is a very
impressive institution, since researchers from all over the world are working
here. It reminds me of a big 'melting pot' of research, because in this
huge complex there are uncounted small labs, one next to the other, and
everybody is working on something different. As it is a governmental institution,
due to the September 11 events, security measures were very strict. Entering
the building in the morning could be quite a hassle, as all bags were x-rayed
and everybody had to go through a metal detector.
With my lab here though, I was very lucky. I had great mentors who supported
me in every possible way, and all the other people working in the lab were
totally nice and always very helpful. I learned a lot about research and
techniques (in theory and practice), and I had the chance to listen to many
interesting talks. In fact, the offerings are so overwhelming that it is
impossible to keep up with everything. I very much enjoyed living in Washington
DC. It is a good-sized city with good public transport (so one doesn't necessarily
need a car). Apart from numerous cafes and restaurants, there are a huge
number of great museums to discover (most of them for free!). Also, there
is the whole government district with the Capitol, the White House and lots
of other important buildings. |
Greatest
Difficulties Encountered
My biggest problem was to get the enzyme I was working with (and which I
brought from Germany) into the country. The fact that it was made from bovine
kidneys didn't make it any easier. Fortunately, Dr. Schnermann managed to
get it out of customs, so that we could store it appropriately, and after
a lot of paperwork, it was finally released and I could work with it. |
Most
humorous incident
I don't know if there was a most humorous incident, but there definitely
were some funny things happening.
When I wanted to join a fitness center, I asked for the conditions. After
explaining everything, the staff person added proudly, "And we have free
parking!!" When I said that I didn't have a car anyway, the stunned response
was, "What do you mean, you don't have car!?"
I also had the most interesting brunch on a Sunday morning in Adams Morgan,
a part of DC well populated by gay people. Aside from serving delicious
food, they performed a great drag-show! Very entertaining!! |
Helpful
Hints for Future Students
If you are planning to go to Washington DC, Bethesda or somewhere nearby,
send me an email and I will try to answer all your questions. I can't think
of any general advice right now other than to enjoy the time and try to
make the best out of it, because it goes by faster than you think it will!
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Abstract
on Research Topic:
Adenosine release is NaCl transport dependent in a macula dens-derived
cell line |
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Author:
A. Luedtke
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Institution
at which research was done:
NIH / NIDDK / MDB, Bethesda, MD |
Purpose:
The juxtaglomerular apparatus is a complex anatomical structure that forms
a link between the vascular pole of the glomerulum and the distal part of
the thick ascending limb of the tubule. Numerous studies have shown that
an increased chloride concentration in the tubule leads to a vasoconstriction
of the afferent arteriole and a reduction of GFR. This mechanism, called
tubuloglomerular feedback (TGF), serves as an intrarenal system controlling
distal NaCl concentration and NaCl excretion. The epithelial cells acting
as NaCl sensors are the macula densa cells. There is evidence to show that
an increase in macula densa NaCl concentration and NaCl transport causes
vasoconstriction by mediation of adenosine. The vasoconstrictor action of
this assumed TGF mediator is caused by activation of adenosine type 1 receptor
on smooth muscle cells of the afferent arteriole. One of the missing links
in this pathway is the identification of the pathway and location of adenosine
formation and release. Furthermore, a dependency of adenosine generation
on NaCl transport has not been demonstrated so far. Using a cultured cell
line of macula densa derived cells, these studies were designed to address
these questions. |
Material
and Methods:
Macula densa cells (MMDD1 cells) were grown in plastic dishes or on permeable
supports in DMEM containing fetal calf serum until reaching confluency.
Adenosine release studies were performed with serum-free medium at a NaCl
concentration of 60 mM. Adenosine concentrations were measured with a sensitive
protein-binding assay using highly purified bovine S-adenosylhomocysteine
hydrolase, which in vitro catalyses the reversible hydrolysis of S-adenosylhomocysteine
into adenosine and homocysteine. In order to avoid metabolism of adenosine
after binding to the enzyme, the enzyme was converted into its reduced,
enzymatically inactive form by replacing the coenzyme NAD+ with NADH. |
Results:
Medium adenosine concentrations were in a range of 67,2 ± 20,8 nM, and were
independent of medium volume. The net adenosine release rate reached a maximum
within 2 seconds and fell thereafter to values close to zero. After preincubation
with a low chloride solution, the initial adenosine efflux was lower than
after preincubation with a normal chloride solution. Furthermore, preincubation
with bumetanide (10-5 or 10-4) caused a reduction in net adenosine release
rate to about half of control. A reduction in medium temperature to 4°C
virtually eliminated net adenosine release. |
Conclusion:
These data demonstrate that a macula densa-derived cell line releases adenosine
until a state of equilibrium is reached at which net adenosine release is
close to zero. We assume therefore that adenosine release takes place through
equlibrative nucleoside transporters (ENT). Net adenosine release decreases
with decreasing NaCl concentration and presumably NaCl transport and following
treatment with bumetanide, an effect that probably reflects a reduction
in intracellular adenosine availability. These data are consistent with
the notion that transport dependent release of adenosine acts as the mediator
in the regulation of afferent arteriolar tone that is the basis of TGF.
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