The increase of passive tension in human skinned cardiomyocytes prestretched under acidic stress and protection by sHSPs. (A) The original recordings for the force response to stepwise cell stretches in relaxing buffer, first at pH 7.4 (black curves) then at pH 6.6 after a 10-min prestretch to 2.6-µm SL in the absence (blue curve) or presence (red curve) of sHSP. (B) Passive tension (F_passive) at pH 7.4 (Control) and at pH 6.6. Cells were not prestretched. (C and E) The F_passive at pH 7.4 (black curve) and at acidic pH after prestretch and hold to a 2.6-µm SL in the absence (blue curve) or presence (red curve) of sHSPs (0.1 mg/ml). Insets in C and E show the reduction of the F_passive (at 2.2-µm SL) in pH 6.6 buffer using sHSP concentrations of 0.01, 0.1, or 1 mg/ml. (D and F) The F_passive at pH 7.4 (black curve) and after a prestretch and hold to a 2.6-µm SL in the absence (blue curve) or presence (red curve) of sHSP (0.1 mg/ml) at normal pH 7.4. HSP27 (C and D) and αB-crystallin (E and F) were used. Data represent means ± SEM (n = 5–10 cells, derived from two human donor hearts); curves represent regression models of order 3; *, P < 0.05, prestretch (pH 6.6) versus prestretch + sHSP (pH 6.6).