Abstract 17013: Transverse (T)-tubules Are Widespread in the Human Atrium
Background: T-tubules are invaginations of the sarcolemma, present in mammalian ventricular myocytes. T-tubules bring the cell interior close to sarcolemmal membrane, allowing a rapid rise in intracellular Ca upon stimulation. The atria was generally assumed to lack t-tubules due to their virtual absence in the atria of small mammals; therefore Ca release occurs only slowly from the cell centre. Recent work has however shown t-tubules in sheep atria resulting in rapid Ca release in the cell interior, fundamentally altering our view of atrial function. Furthermore atrial t-tubules are lost in disease, dramatically slowing intracellular Ca. The purpose of this study was to determine if the human atrium possesses t-tubules.
Methods: Samples of right atrial appendage from 9 patients in sinus rhythm were frozen in OCT, sectioned, fixed and incubated with wheat germ agglutinin (WGA)-, Alexa Fluor® 488 conjugate to stain t-tubules and surface membrane. Image stacks were captured confocally, deconvolved and analyzed in Image J.
Results: T-tubules were present in each sample. The figure shows a transverse, 2 μ m thick human atrium section following staining. T-tubules are clearly present in 3 cells to varying degrees. T-tubules were present in 59 from 86 cells (51 tissue sections) i.e. 69% of human atrial cells. To quantitatively assess the importance of t-tubules in bringing the cell interior close to sarcolemmal membrane we have calculated the distance that points in the cell lie from the surface sarcolemma and surface and t-tubular sarcolemma together. Excluding t-tubules, half the points lie within 2.2 ± 0.2 μ m of sarcolemma and this distance is approximately halved by considering surface and t-tubule sarcolemma together (1.0 ± 0.2 μ m; p<0.001, n=9 cells from 4 patients).
Conclusion: We have shown, for the first time, the presence of t-tubules in human atrium. The role of human atrial t-tubules during excitation contraction coupling and disease remains to be determined.
- © 2011 by American Heart Association, Inc.