Low-threshold calcium currents in central nervous system neurons.

The low-threshold calcium current, or T current, has recently been demonstrated with voltage-clamp recordings in a variety of central nervous system (CNS) neurons. It is especially prominent in the soma and dendrites of neurons with robust calcium-dependent burst firing behaviors such as thalamic relay neurons and cerebellar Purkinje cells. Single-channel and macroscopic current behavior have been carefully investigated and kinetic schemes devised to completely describe the activation and inactivation processes. The kinetic properties of T current lead to activation of low-threshold spikes subsequent to transient membrane hyperpolarizations. Putative functional roles for T current include generation of low-threshold spikes that lead to burst firing, promotion of intrinsic oscillatory behavior, boosting of calcium entry, and synaptic potentiation.