(or funny channel
, or If
) refers to a specific current in the heart
. It is called "funny" because it has effects opposite to those of most other heart currents.
If is a mixed Na+–K+ inward current activated by hyperpolarization and modulated by the autonomic nervous system. It is one of the most important ionic currents for regulating pacemaker activity in the sinoatrial (SA) node.
Most channels are activated through depolarization, but in the SA node and AV node, the channel becomes activated through hyperpolarization, at approximately -40mV.
Funny currents have been associated with cyclic-nucleotide-gated channels.
Drugs such as ivabradine are intended to inhibit the funny current, and thus slow down the heart rate. Ivabradine selectively inhibits the pacemaker If current in a dose-dependent manner.
- Accili E, Proenza C, Baruscotti M, DiFrancesco D "From funny current to HCN channels: 20 years of excitation.". News Physiol Sci 17 32–7.