Molecular properties of voltage-sensitive sodium channels.

Voltage sensitive calcium channels participate in action potential generation in electrically excitable cells and constitute an essential link between transient changes in membrane potential and a variety of cellular responses including secretion of neurotransmitters and hormones, initiation of contraction in cardiac and smooth muscle, and activation of second messenger responses in many cell types. Electrophysiological measurements have established the existence of multiple classes of calcium channels.1–4 Although work on many cell systems has contributed to current understanding of calcium channel function, the molecular properties of the channel have been investigated most thoroughly in skeletal muscle which has a particularly high density of calcium channels. This chapter will therefore focus primarily on skeletal muscle calcium channels.