DALLAS -- Myoglobin, the protein long thought to be the sole carrier of
oxygen to heart and certain skeletal muscle, is not necessary for survival, UT
Southwestern Medical Center at Dallas scientists reported in the October 29
issue of the journal Nature.
Because of this discovery, investigators will be able to delve further into
causes, prevention and cures for heart failure. The researchers made their
breakthrough by developing a strain of mice lacking the gene to produce
myoglobin, which transports oxygen from capillaries to mitochondria in heart
and endurance muscle cells. Mitochondria are the structures within cells that
transform oxygen and other molecules into energy for all cellular functions.
"Myoglobin is found in the heart and the slow-twitch, or endurance, skeletal
muscles in a number of species. So because of its prevalence and the energy
required for contraction of the heart, we predicted that mice could not live
without this protein," said Dr. Dan Garry, assistant professor of internal
medicine and first author of the report. "We were surprised that not only did
they survive without it, they were born, developed, reproduced, nurtured and
exercised normally."
The mice were exercised on treadmills along with littermates that had
myoglobin. All the animals were exposed to conditions simulating different
altitudes at which the body would normally experience some lack of oxygen.
Neither group showed any differences in their behavior or their ability to
handle the different conditions.
The only alteration researchers found in the rodents lacking myoglobin was
that the heart and endurance muscles were nonpigmented or almost white
rather than a rich pink because most of the red color actually comes from the
myoglobin. "Our research suggests that the system transferring the oxygen
necessary to fuel the contraction of heart and slow-twitch muscles is much
more complicated than the long-held paradigm," Garry said.
Now, the researchers will look for other genes that are expressed at a higher
level in the genetically altered mice during times when they are exposed to
conditions where their hearts and endurance muscles need more oxygen. In
studying these genes, the investigators may be able to discover the system that
enables the heart and skeletal muscles to get the energy they need to continue
functioning.
"We still believe that myoglobin is important, but something else is also
important; there are some cellular adaptations that we have not yet defined,"
Garry said. "By understanding and identifying these adaptations, we will
increase our knowledge of what happens when people get chest pains. This
will impact our treatment of patients who suffer from coronary-artery disease."
The other researchers on the study were: Dr. George Ordway, associate
professor of physiology; Dr. Nina Radford, assistant professor of internal
medicine; Dr. Eva Chin, postdoctoral fellow in internal medicine; Dr. Robert
Grange, assistant instructor of physiology; Dr. Rhonda Bassel-Duby, associate
professor of internal medicine; Dr. R. Sanders Williams, chief of cardiology,
director of the Frank M. Ryburn Jr. Cardiac center and holder of the James
T. Willerson, M.D., Distinguished Chair in Cardiovascular Diseases; and Dr.
John Lorenz, Department of Molecular and Cellular Physiology, University of
Cincinnati.
This work was supported by grants from the National Institutes of Health and
the American Heart Association.
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From: Cliff Lundberg[SMTP:cliff@noevalley.com]
Sent: Tuesday, November 03, 1998 1:43 AM
To: evolution@calvin.edu
Subject: Re: Evolution of redundancy
Pim van Meurs wrote:
> I got into an argument about redundancy as evidence of design.
> My question is how would evolution explain redundancy ?
What sort of redundancy are you talking about? Examples?
-- Cliff Lundberg ~ San Francisco ~ cliff@noevalley.com