Friday, August 21, 1998 Published at 15:31 GMT 16:31 UK
Muscles breakthrough could combat disease
Scientists can simulate the impact of exercise on the muscles
A breakthrough in the understanding of how muscles work could pave the way for new treatments to restore tissue wasted by disease such as diabetes and heart failuire.
The discovery may allow scientists to develop drugs that mimic the effects of exercise - which naturally produces muscle needed for endurance.
A team at the University of Texas has discovered a genetic switch that controls muscle action.
Writing in the journal Genes and Development, the researchers said they had identified the molecular pathway in rats that controls the action of a muscle fibre.
Two types of muscle
The human body has two types of muscle, fast twitch, which provides strength, and slow twitch, which provides endurance.
The scientists have discovered a mechanism that induces the muscles to become slow.
This pathway is stimulated naturally by taking exercise such as jogging where endurance is vital, but the new discovery could allow artificial manipulation.
Dr Williams's team identified three proteins, known as calcineurin, NFAT and MEF2 that combine to activate muscle genes.
Stimulated by exercise
When a muscle is constantly stimulated by exercise such as jogging, calcium ions build up inside the muscle cell and activate calcineurin.
This in turn causes NFAT to combine with MEF2 to switch on the genes that control the action of new muscle fibres, and ensures that they provide the slow-release energy needed for endurance.
The team is now doing tests to see if this pathway is the same one used in humans and if so, if it could be activated by a drug.
They hope that unused muscle, which is in a state similar to the "fast" twitch state, can be stimulated by this pathway.
No slow muscle
Team member Dr Rhonda Bassel-Duby said: "Patients that are lying in bed or are immobilised don't have slow muscle.
"Our ultimate goal is to be able to design a drug that will convert their fast muscle to slow. They need slow muscle to be able to get out of bed and walk around for an extended period, rather than just one or two minutes."
Unfortunately, any such drug would not strengthen the heart. The pathway exists only in skeletal muscles -- the ones that move the limbs.