The large nerve axon of the squid has been widely used in studies of the mechanism of conduction of electric impulses.
represents proteins, which have a net negative charge at the neutral pH of blood and cells.
example, up to 25 percent of the ATP produced by nerve and kidney cells is used for ion transport, and human erythro-cytes consume up to 50 percent of their available ATP for this purpose; in both cases, most of this ATP is used to power the Na+/K+ pump.
In cells treated with poisons that inhibit the aerobic production of ATP (e.g., 2,4-dinitrophenol in aerobic cells), the ion concentrations inside the cell gradually approach those of the exterior environment as ions move through channels in the plasma membrane down their electrochemical gradients. Eventually treated cells die: partly because protein synthesis requires a high concentration of K+ ions and partly because in the absence of a Na+ gradient across the cell membrane, a cell cannot import certain nutrients such as amino acids. Studies on the effects of such poisons provided early evidence for the existence of ion pumps.
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