what is it's significance clinically?
They may be lost or disrupted following a myocardial infarction, and are also disrupted in the ventricles of patients with heart failure, contributing to reduced force of contraction and potentially decreasing the chances of recovery.
T-tubule
T-tubules may be lost or disrupted following a myocardial infarction, and are also disrupted in the ventricles of patients with heart failure, contributing to reduced force of contraction and potentially decreasing the chances of recovery. 
the function of the transverse tubules is to T-tubules permit rapid transmission of the action potential into the cell, and also play an important role in regulating cellular calcium concentration. when was it first introduced? They were discovered in 1897.
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T-tubule [SEP] Clinical significance
The structure of T-tubules can be altered by disease, which in the heart may contribute to weakness of the heart muscle or abnormal heart rhythms. The alterations seen in disease range from a complete loss of T-tubules to more subtle changes in their orientation or branching patterns. T-tubules may be lost or disrupted following a myocardial infarction, and are also disrupted in the ventricles of patients with heart failure, contributing to reduced force of contraction and potentially decreasing the chances of recovery. Heart failure can also cause the near-complete loss of T-tubules from atrial cardiomyocytes, reducing atrial contractility and potentially contributing to atrial fibrillation.