58 THE SCIENTIST | the-scientist.com
PROFILEtiny indented structures in the surface membrane of individual
muscles that are also found in fat tissue and in blood vessels. The
pair found that the thousands of caveolae in frog muscle open,
enabling the muscle to survive “enormous stretches to more than
double its rest length and without significant damage to the cells,”
says Dulhunty. Their findings revealed just how well-equipped
muscle is to adapt to stress and resist cell death.
Dulhunty stayed in the US for a year and a half. When she wasn’t in
the lab, she took time to travel, visiting Woods Hole in the summer, and
taking a three-week road trip from the East Coast to the West Coast and
back to Rochester in a “little Mustang car.” Still, she wanted to go back
to Australia. And, she wanted to find out more about how mammalian
muscles worked, which other researchers were not yet attempting.
After leaving Rochester in 1974, Dulhunty started her own lab
at the University of Sydney. Her goal was to better understand how
the electrical signal on the surface membrane of a muscle cell is
translated into the release of calcium ions that initiates muscle
contraction. Dulhunty homed in on how ion channels in the mus-
cle affect membrane potential—the difference in electric poten-
tial between the interior and the exterior of a living cell. Her first
achievement on this front, in 1977, was authoring a Nature paper
that revealed details of mammalian muscle contraction. She found
that the threshold of response to potassium ions is higher in rat
muscle than in amphibian muscle. Dulhunty then went on to dem-
onstrate the importance of chloride ions and membrane-bound
chloride transporter proteins in setting the electrical membrane
potential in mammalian skeletal muscle.
“It was assumed that chloride functioned the same way in
amphibians and in mammals, but we found chloride ion func-
tion was very different from that in amphibian muscle,” Dulhunty
explains. The studies helped uncover what goes wrong in several
human childhood-onset genetic neuromuscular disorders, includ-
ing myotonia congenita and myotonic dystrophy. Both occur when
chloride channel presence is altered in muscle. Largely following
from Dulhunty’s work, researchers have shown that the removal of
chloride ions from the muscle membrane results in overexcitable
muscle fibers that contract involuntarily.BUILDING A LAB
In 1984, Dulhunty moved her laboratory to Australian National
University in Canberra. By then she and Gage were a couple, and
he also moved his lab to the university, where the two continued to
collaborate until his death in 2005.
Once her lab was established, Dulhunty continued to develop
techniques to study mammalian muscle. There was a gradual tran-
sition in the field from examining the biophysical properties of
amphibian muscles—which are much easier to study—to mamma-
lian muscle, in large part led by Dulhunty.
Her group was the first to measure the “asymmetrical charge
movement” in mammalian muscle fibers. The phenomenon—ini-
tially identified in nerve and then muscle cells—arises when a charge
moves about a millionth of a millimeter inside the cell membrane,
which is a critical part of normal muscle fiber contraction. To makethis exquisite measurement in the mammalian system, Dulhunty’s
and Gage’s labs first had to design and build the equipment for doing
so, putting three tiny, glass pipette electrodes into the end of an indi-
vidual rat muscle fiber and painstakingly dissecting the minute elec-
trical signals of asymmetrical charge movement from much larger
signals and noise in the system. The signals had been predicted in the
1950s by the 1963 Nobel Prize winners Alan Hodgkin and Andrew
Huxley, but it had taken more than 20 years to develop the technology
required to measure so tiny a charge movement. “It was very exciting
to be a part of that development,” Dulhunty says.
Researchers in Dulhunty’s lab also began to study the ryanodine
receptor ion channel. Among the first to characterize the receptor,
Dulhunty’s lab extracted the essential protein from muscle fibers,
embedding it into an artificial lipid bilayer to study its function.
The receptor works to initiate the final step of muscle contraction.
In 1994 and 1995, the team found that a small, multifunctional
protein that binds an immunosuppressant drug, FK506, was criti-
cal for normal ryanodine receptor function. They also discovered
unsuspected effects of high calcium ion concentrations and oxi-
dizing reagents on the activity of the receptor in cardiac muscle.
“Everything that the lab has done since then has been partly focused
on this ion channel and the way in which it operates, including its
role in human muscle diseases,” Dulhunty says.
The study of the transferases and related proteins is an exam-
ple. In 2012, she and her colleagues found that a mutation in the
gene for human CLIC-2, the type 2 chloride intracellular ion chan-
nel, could result in X-linked intellectual disability, congestive heart
failure, and seizures. “The mutation altered the effect of CLIC-2
on the ryanodine receptor, so altering normal ryanodine receptor
activity could explain the characteristics of individuals carrying this
mutation,” Dulhunty says. More recently, in still unpublished work,
the lab identified additional disease-associated CLIC-2 mutations.
An emeritus professor since 2016, Dulhunty is wrapping up
a few key projects, including identifying additional proteins that
interact with the ryanodine receptor. She also has been working
with a foundation in the US to develop animal models for ryanodine
receptor–associated muscle diseases. The lab, which comprises one
technician and one graduate student, contributes by exploring how
the activity of the ryanodine receptor is affected by genetic altera-
tions. “It’s important to study these human mutations in animal
models, not just in cell culture, because there are major differences
of how muscle proteins are modified in a whole animal compared
to in isolated cell cultures,” Dulhunty says.
She is optimistic about further advances in the field. “When I
started my PhD, muscle contraction was a black box, and now we
generally know how it works, although not all of the most impor-
tant details,” she says. The next generation of scientists, she says, will
have to develop new techniques to reveal these details.
Dulhunty says that in retirement she hopes to help researchers
in her lab and to set aside time to tend her horses. “A s soon as I had
enough money, I bought my own horse,” Dulhunty says. That was
30 years ago. She now lives on farm with two Jack Russell terriers
and two horses, which she tries to ride five times a week. g