Mechanisms causing plateau potentials in spinal motoneurones.

Plateau potentials are generated by a voltage sensitive persistent inward current. In spinal motoneurones this current is predominantly mediated by influx of Ca2+ through L-type Ca2+ channels of the Ca(v)1.3 subtype. Depolarisation-induced facilitation of L-type Ca2+ channels is thought to be the mechanism for delayed activation (wind-up and warm-up) of the plateau potential and for the hysteresis in firing frequency and I-V relation during triangular depolarisation. L-type Ca2+ channels and plateau potentials in spinal motoneurones are facilitated by activation of metabotropic receptors for glutamate, acetylcholine, noradrenaline and serotonin and down regulated by activation of GABA(B) receptors. The facilitation has been shown to depend on activated calmodulin.