A Summary Ion Channels In The NerveCell — страница 2

proteins, that make analyzing the channel molecules difficult. Potassium channels, while just as important as sodium channels, are even more difficult to study. This is due the fact that there is no analogue of tetradotoxin for potassium channels, and because their opening has a ten second delay, and is much slower than that of sodium channels. This makes gating current measurements nearly impossible to obtain. However, some studies on electrical noise have provided the estimate that there is perhaps one potassium channel for every 10 sodium channels in an axon?s membrane. There are three types of currents described in the article: ionic current, gating current, and displacement current. Ionic current is the measure of the charge flow that results from the movement of ions

(sodium and potassium) through ion channels in the cell membrane, and involves 100 sodium ions in one nerve impulse. The gating current is much smaller than the ion current, it only involves the transfer of about four electronic charges, and it is the measure of the gating particles as they move to their ?open? configuration. The gating current is induced by depolarization of the nerve cell. The displacement current in a nerve cell is composed mostly of the gating current but is also partly due to the, ?charging and discharging of the large static capacity of the membrane.? This current is recorded when the potential of a voltage-clamped cell is suddenly altered with a pulse. By comparing the displacement current values resulting from hyperpolarizing and depolarizing pulses, the

gating current can be deducted from the total displacement current.