Protein-channel HCN

See also the page of homonymy HCN

The protein-channel HCN (of the English Hyperpolarisation-activated Cylic-Nucleotid modulated Cation Not-selective Chanel , i.e. channel activated by the hyperpolarisation, modulated by the Nucleotide S cyclic and nonselective with the cations) are ionic Canaux which open in answer to a hyperpolarisation of the membrane. They generate a current activated by the hyperpolarisation, also called running I_h. It was described independently in the Cœur and the central Nervous system. This is why it was named I_Q (for queer , strange) and I_f (for funny , funny). Certain authors speak about cation current rectifying entering , because it acts like a Rectifieur. As it is permeable at the same time with the Potassium and the Sodium, them Potentiel of inversion E_rev is located around -30mV, which depolarizes the cell in the range of potential where the others channels depending on the voltage can be activated.

Properties

The funny current ( funny current ) was initially discovered in the cells of the sinusal Nœud of the Cœur in 1976 at the rabbit. Two unusual properties were worth to him are first name:

an activation by the hyperpolarisation (the major part of the currents known are activated by a depolarization)
a low selectivity between sodium and potassium.

The I_f current was recognized as implied in the autonomous generation of rate/rhythm. This is why it was also called " channel pacemaker ". It is in fact responable of the diastolic depolarization .

In the years

Distribution

Biophysics

Physiological roles

Generator of rate/rhythm (" Pacemaker")

The presence of the Ih current and the current I_T makes it possible to generate a rate/rhythm:

following a Potential of action, a massive entry of Potassium hyperpolarise the cell
this hyperpolarisation activates the Ih current, and raises the inactivation of the current I_T
the Ih current, whose kinetics of activation is slow, repolarise with a certain time the cell
arrived at the threshold of activation of the I_T current, this one opens, the cell is strongly depolarized by the calcium entry.
a new potential of action takes place, the cycle starts again.

Gràce with the kinetics of the current Ih, the period of the cycle is very precise. Modulations of the kinetics of the Ih current by AMPc permettents to vary the frequency of the rates/rhythms.

In the Heart

In the Thalamus

Integration of the nervous signal

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