Courant calcique de type T

T-type calcium channels are low voltage activated calcium channels that become inactivated during cell membrane hyperpolarization but then open to depolarization. The entry of calcium into various cells has many different physiological responses associated with it. Within cardiac muscle cell and smooth muscle cells voltage-gated calcium channel activation initiates contraction directly by allowing the cytosolic concentration to increase. Not only are T-type calcium channels known to be present within cardiac and smooth muscle, but they also are present in many neuronal cells within the central nervous system. Different experimental studies within the 1970s allowed for the distinction of T-type calcium channels (transient opening calcium channels) from the already well-known L-type calcium channels (Long-Lasting calcium channels). The new T-type channels were much different from the L-type calcium channels due to their ability to be activated by more negative membrane potentials, had small single channel conductance, and also were unresponsive to calcium antagonist drugs that were present. These distinct calcium channels are generally located within the brain, peripheral nervous system, heart, smooth muscle, bone, and endocrine system. The distinct structures of T-type calcium channels are what allow them to conduct in these manners, consisting of a primary α1 subunit. The α1 subunit of T-type channels is the primary subunit that forms the pore of the channel, and allows for entry of calcium. T-type calcium channels function to control the pace-making activity of the SA Node within the heart and relay rapid action potentials within the thalamus. These channels allow for continuous rhythmic bursts that control the SA Node of the heart. Pharmacological evidence of T-type calcium channels suggest that they play a role in several forms of cancer, absence epilepsy, pain, and Parkinson's disease. Further research is continuously occurring to better understand these distinct channels, as well as to create drugs to selectively target these channels.