<Tr> <Th> TH </Th> <Td> H2. 00.05. 2.01018, H2. 00.05. 2.02013 </Td> </Tr> <Tr> <Td_colspan="2"> Anatomical terminology (edit on Wikidata) </Td> </Tr> <P> Transverse tubules (T - tubules) are extensions of the cell membrane that penetrate into the centre of skeletal and cardiac muscle cells . With membranes that contain large concentrations of ion channels, transporters, and pumps, T - tubules permit rapid transmission of the action potential into the cell, and also play an important role in regulating cellular calcium concentration . Through these mechanisms, T - tubules allow heart muscle cells to contract more forcefully by synchronising calcium release throughout the cell . T - tubule structure may be affected by disease, potentially contributing to heart failure and arrhythmias . Although these structures were first seen in 1897, research into T - tubule biology is ongoing . </P> <P> T - tubules are tubules formed from the same phospholipid bilayer as the surface membrane or sarcolemma of skeletal or cardiac muscle cells . They connect directly with the sarcolemma at one end before travelling deep within the cell, forming a network of tubules with sections running both perpendicular (transverse) to and parallel (axially) to the sarcolemma . Due to this complex orientation, some refer to T - tubules as the transverse - axial tubular system . The inside or lumen of the T - tubule is open at the cell surface, meaning that the T - tubule is filled with fluid containing the same constituents as the solution that surrounds the cell (the extracellular fluid). Rather than being just a passive connecting tube, the membrane which forms T - tubules is highly active, being studded with proteins including L - type calcium channels, sodium - calcium exchangers, calcium ATPases and Beta adrenoceptors . </P>

T or transverse tubules in skeletal muscle function to