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T-type calcium channels are low-voltage activated calcium channels that open during membrane depolarization. These channels aid in mediating calcium influx into cells after an action potential or depolarizing signal. The entry of calcium into various cells has many different physiological responses associated with it. Within cardiac and smooth muscle cells voltage-gated calcium channel activation initiates contraction directly by allowing the cytosolic calcium concentration to increase. Not only are T-type calcium channels known to be present within cardiac and smooth muscle, but 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.〔(【引用サイトリンク】url=http://www.medandlife.ro/medandlife560.html )〕 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 key role in diseases such as absence epilepsy, diabetes, and several forms of cancer. Further research is continuously occurring to better understand these distinct channels, as well as create drugs to select for these channels. == Function == Like any other channel in a cell membrane, the primary function of the T-type voltage gated calcium channel is to allow passage of ions, in this case calcium, through the membrane when the channel is activated. When membrane depolarization occurs in a cell membrane where these channels are embedded, they open and allow calcium to enter the cell, which leads to several different cellular events depending on where in the body the cell is found. As a member of the Cav3 subfamily of voltage-gated calcium channels, the function of the T-type channel is important for the repetitive firing of action potentials in cells with rhythmic firing patterns such as cardiac muscle cells and neurons in the thalamus of the brain.〔 T-type calcium channels are activated in the same range as voltage-gated sodium channels, which is at about -55 mV. Because of this very negative value at which these channels are active, there is a large driving force for calcium going into the cell. The T-type channel is regulated by both dopamine and other neurotransmitters, which inhibit T-type currents. Additionally, in certain cells angiotensin II enhances the activation of T-type channels.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「T-type calcium channel」の詳細全文を読む スポンサード リンク
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