Page 64 - Consciousness in the Cell

CONSCIOUSNESS IN THE CELL

NITRIC OXIDE: THE MIRACLE MOLECULE THAT

D›LATES BLOOD VESSELS

Three scientists who won the 1998 Nobel Prize in Physiology or
Medicine discovered that molecules of nitric oxide (NO), released
by blood vessels, had the ability to relax them. The NO molecule
regulates tension in the walls of blood vessels, but doesn't carry
out this act by itself. Rather, it functions as a mediator in relaxing
the blood vessel.
To understand how this cascade process works, examine the
diagram on the next page. For the vessels to relax, first of all some
hormones in the blood start the process by sending an alert, bind-
ing to receptors found in the blood vessel lining. We can compare
this to a domino effect, when a single domino falls and brings
down a whole row of others. Immediately after the hormone sets
off an alert signal by binding to the receptor, the vessel lining "real-
izes" what it must do and begins producing nitric oxide. Some of
the NO molecules, "knowing" what they have to do as soon as they
are released, head quickly for the vascular smooth muscle cells.
Entering the cells, they bind to an enzyme.
This is the second step. But in order for the vessel to relax, yet
a third step must be reached. Once NO has combined with the
enzyme in the smooth muscle cell, GTP (guanosine triphosphate)
is converted to cyclic guanosine monophosphate, or cGMP.
Obviously, this newly synthesized molecule has a role to play in
this cascade and, to bring this about, it makes its way to myosin.
Myosin is a necessary protein needed in the contraction and relax-
ation of muscle cells. Here, the final step has been reached. With
the action of myosin the last domino falls, and the muscle cells
relax.
Reviewing these steps again, we see that the hormones and

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