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Common neurotransmitters can convert sodium channels in the membranes of biological cells into calcium channels. Since both channel types are widespread in the human body, scientists are hoping for a new therapeutic approach for heart, nerve, brain and muscle diseases. W. J. Lederer and co-workers at the University of Maryland Biotechnology Center described in Science February 13, 1998 that common neurotransmitters such as adrenaline and medicinal agents such as digitalis can induce the conversion of sodium channels to calcium channels.
Sodium channels are proteins that regulate electrical activity in nearly all excitable cells in the body. This includes the neurons, sensory cells in the eye and ear, muscle cells, and any other cell whose membrane voltage changes rapidly.
Calcium channels allow calcium ions into the cells and thereby influence their activities. They control the heartbeat and the conversion of sound and light into what we call hearing and seeing. They are also believed to be involved in decoding our memory in the brain.
"We found out that sodium channels can be induced by a neurotransmitter like adrenaline to do something new and completely different than usual: they conduct calcium," said Lederer. "And when a sodium channel in the heart muscle conducts calcium, it clearly amplifies the contraction."
According to him, the flow of calcium ions through sodium channels is a new signaling pathway in cells, which he has termed slip-mode conductance of the sodium channel. Controlled by hormones and neural activity, the system could be switched on and off. Since the structure of the sodium channel is almost exactly the same in different tissues and organisms, it is reasonable to assume that the results can be extrapolated to all excitable cells, although they were obtained in experiments with heart cells.
The results could explain how traditional medicines like digitalis work to treat heart defects. But Lederer sees a much greater benefit in the completely new approach to the development of future drugs and molecular medicine. Substances that are effective against heart defects could not only be found, therapies against neuronal, brain and muscle diseases are also conceivable.
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