VPB 121: Veterinary Physiology - II (2+1)

THE VOLTAGE-GATED POTASSIUM CHANNEL

• This channel has only one gate at the interior of the membrane and closes or opens to the interior of the cell.  The opening of the gate is referred to as activation. The gate operates in two stages:
• Resting stage: During the stage the gate is closed and the K⁺ is prevented from passing to the exterior of the cell through the channel.

During the stage of action potential manifestation

• When the membrane potential, rises from -80mV toward zero (becomes less negative).  This voltage change causes conformational opening of the gate and allows K⁺ diffusion outward.  But, this process operates in a slow manner hence, it is timed, that the opening of the K⁺ channel is initiated at the same time that the Na⁺channels are becoming inactivated (closing).  The later decreases the Na⁺ entry into the cells.
• Thus the decreased Na⁺ entry to the cell and concomitant increase in K⁺ exit from the cell increases the intracellular negativity and greatly speeds the repolarization process. Therefore, in a fraction of a second (few 10,000ths of a second) there is attainment of the resting membrane potential.