The T-type calcium channel is a type of voltage-dependent calcium channel, the alpha1 subunit determines most of the channel"s properties. The T-type calcium channel is one of the components that produce the pacemaker potential in the SA node of the heart. T-type calcium channel blockers are used primarily as antiepileptics. Two voltage-dependent calcium channels play critical roles in the physiology of cardiac muscle: L-type calcium channel and T-type calcium channels voltage-gated calcium channels. L-type channels are important in sustaining an action potential, while T-type channels are important in initiating them.