|MadSci Network: Biochemistry|
I think you are actually talking about two or three different things here. There are ion pumps which require ATP to be hydrolyzed to pump an ion across the membrane, there are ion exchangers which exchange one or more of a certain ion on one side of the membrane for one or more ions on the other side of the membrane; and there are ion channels which are usually selective for a certain type of ion and can be opened by a number of methods including voltage, ligand binding and constitutive avtivity. These pumps you are reffering to I think are cation specific ligand gated ion channels. To initiate a nerve impulse in a typical neuron, the voltage of the membrane must increase to a more positive potential (typically for -70mV to -40mV). The way this is accomplished is through the activatio or opening of ligand-gated ion channels which open in response to a neurotransmitter binding to the channel allowing cation into the cell and rasing the internal cation concentration thereby making the membrane voltage more positive and binding to the channel allowing cation into the cell and rasing the internal cation concentration thereby making the membrane voltage more positive and with enough channels being opened the threshhold for voltage-gated Na channel activation is reached and the action potential is fired. Dmitri
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