Treatments for certain human conditions involve signaling pathways. One pathway uses cyclic GMP, or cGMP, as a signaling molecule. Its effects include the relaxation of smooth muscle cells in artery walls. A compound was developed to treat chest pains. This compound inhibits the hydrolysis of cGMP to GMP, prolonging the signal and increasing blood flow to the heart muscle. Under the trade name Viagra, this compound is now widely used as a treatment for erectile dysfunction. Viagra causes dilation of blood vessels, allowing increased blood flow to the penis. Many signal molecules in animals induce responses in their target cells via signal-transduction pathways that increase the cytosolic concentration of Ca 2+ . In animal cells, increases in Ca 2+ may cause contraction of muscle cells, secretion of certain substances, and cell division.
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