Hyperpolarization (biology)
As hyperpolarization (engl. Hyperpolarization ) or hyperpolarization is called in the biology and physiology of an increase in the membrane voltage of a sensory, nerve or muscle cell via the quiescent value , which means that the voltage between the inner and outer side of the membrane is more negative . The hyperpolarization takes place by activating inhibitory synapses , by opening or closing certain ion channels or by applying a voltage of suitable polarity to the excitable membrane. Hyperpolarization is the opposite of depolarization , in which the potential inside the cell becomes more positive. The hyperpolarization also raises the threshold for triggering an excitement - in the sense of an inhibition. The term can either be used synonymously for the repolarization or only for the subsequent post-hyperpolarization.
In the context of an action potential that leads to the excitation of a cell membrane, shortly after the completed phase of depolarization, the opening of the voltage-dependent K + channels and Cl - channels initially causes the phase of repolarization , in which the membrane potential drops to the resting potential of around −70 mV returns, as well as a fall below this resting potential by about 10 to 30 mV to about −100 mV. The reason for this is that it takes a long time to close the potassium channels when the resting potential is reached and during this time potassium continues to diffuse. This hyperpolarization following the repolarization is also called “postpotential”. It is assumed that the hyperpolarization could serve to make the Na + channels excitable again as quickly as possible.
In photoreceptor cells, the rest potential is around −40 mV because of the dark current . The absorption of photons triggers a signal cascade that leads to the closure of cGMP -dependent Na + channels. This in turn causes a hyperpolarization of the membrane, which translates the external stimulus (light) into an electrical signal (change in membrane potential).