Figure 5.

High wall stress induces t-tubule disruption and loss in vitro. Papillary muscles were isolated, mounted in a Myobath system, and maintained under culture conditions for 48 h during 0.5 Hz stimulation. Muscles were exposed to modest pre-load (diastolic stress ≈4 kN/m²) or elevated diastolic stress approximating that observed during end-diastole in the proximal zone (15–20 kN/m²). (A) Representative recordings of diastolic and systolic stress for the two treatment groups during the protocol. Visualization of t-tubules by caveolin-3 immunostaining after the 48 h incubation period revealed well-maintained t-tubular structure in the low-wall stress group, but marked t-tubule disruption following high wall stress (B). Overall t-tubule density was reduced by exposure to high wall stress (C) and included loss of both transverse and longitudinal elements [D and E, low wall stress: n = 67 cells from five muscles (4 hearts), high wall stress: n = 64 cells from five muscles (three hearts)]. T-tubule loss was associated with a marked decrease in relative junctophilin-2 mRNA expression in the high-wall stress group (F, n_muscles = 4, 3 in low, high wall stress groups, respectively). LWS, low wall stress; HWS, high wall stress (*P < 0.05 vs. low wall stress).