Some human diseases the result of faulty membrane transport systems. An example would be type II (adult onset) diabetes mellitus. Excess glucose in the bloodstream, caused by eating a meal rich in carbohydrates, is usually taken up by myocytes (muscle cells) and adipocytes (fat cells). The glucose transporter GluT4 is normally present in the cell membrane in small amounts. The presence of insulin (a hormone secreted by the pancreas in response to high glucose levels) causes more GluT4 transporters to be exposed, increasing uptake of glucose into the cell. In type II diabetes there is resistance to the metabolic effects of insulin, either at the cell membrane or in post-receptor signaling systems. This means that little glucose can be taken up by myocytes and adipocytes, and high blood glucose levels are the result.
Cystic fibrosis. a genetic disease, causes an abnormality in the mucus normally found in the lungs, resulting in increased bacterial infections and difficulty breathing. This is caused by a defective chloride and fluid transport that decreases the water content of the mucus and causes it to be excessively thick.
Other disorders of membrane transport include Giddleman's syndrome and Liddle's syndrome, which can cause either hypo- or hypertension. Membrane disorders are also important causes of water and electrolyte disturbances, disorders of neural transmission, and many other syndromes.
Hazardous substances such as tetrodoxin (produced by the puffer fish), dendrotoxin (venom of the black mamba snake), and cobrotoxin (another snake venom) affect the function of different ion channels in neurons, blocking signals from the nervous system to muscles. The result may be paralysis and in some cases, death.
Stephanie Islane Dionne, The Gale Group Inc., Gale, Detroit,