The role of voltage-gated calcium chanels in regulating the excitability and discharge behavior of motoneurons
The discharge behavior of mammalian motoneurons is governed by a complex interplay between the excitatory and inhibitory synaptic inputs they receive and the cells’ intrinsic electrical properties. Motoneurons express a host of voltage-gated channels that can dramatically alter the transmission of synaptic current to the soma and the integration of different synaptic input systems. Of particular importance are the Cav1.2 and Cav1.3 channels that are a major source of the persistent inward current (PIC) that amplifies excitatory synaptic input and supports repetitive firing. Indeed, PICs provide an intrinsic source of excitatory drive that is larger than those associated with any of the synaptic input systems studied to date. Whereas PICs can be rapidly inactivated by a hyperpolarizing input, they are ideally suited for both supporting sustained muscle contractions in posture and for providing a major source of the alternating ‘drive’ to motoneurons during locomotion. In my lecture, I will review our studies conducted over the past decade on the biophysical properties of Cav1.2-1.3 channels using electrical, immunocytochemical and optical methods. My goal is to elucidate how the properties of these channels studied in reduced, in vitro preparations can account for many of the complex behaviors of motoneurons observed in intact animals and in man.