Queer channels in hippocampal basket cells: h-current without sag

摘要

currents (4) observed in the heart and the brain, have puzzled physiologists since their initial discovery 25 years ago, Unlike most voltage-gated channels, Ih channels (or h-channels) are activated by hyper polarizing voltage steps to potentials more negative than -60 mV but are not inactivating, Their reversal potential near -30 mV imposes a depolarizing current near the resting membrane potential. Thus, h-channels control the resting membrane potential and the input resistance. Their presence is typically signalled in current clamp records by a depolarizing deflection (also termed 'sag') in response to hyper-polarizing pulses of current. These channels oppose not only hyper polarizations but also depolarizations via their slow deactivation. As a result the h-current has also been designated If for 'funny' or Iq for 'queer' A family of four mammalian genes encoding the Hyperpolarization-activated and Cyclic Nucleotide-gated cationic subunits (HCN1-4), which in the form of tetramers build h-channels, has been identified, making it now possible to address the physiological role of Ih at the molecular level. The targeting of HCN channels is controlled by Trip8b, a Rab-interacting brain-specific protein (Santoro et al. 2004).