FIGURE 7.

Expression of ssTnIN141H 6 days after gene transfer (A, B) and influence on myofilament Ca²⁺ sensitivity of force at pH 7.0 and 6.2, 5–6 days after gene transfer (C). A. Representative expression of ssTnIN141H, and comparison to non-infected control myocytes and myocytes treated with adenoviral vectors for cTnI and ssTnI 5–6 days after gene transfer. Similar results were obtained in intact and permeabilized myocytes 6 days after gene transfer (results not shown). B. Immunhistochemical staining of troponin I showing a striated pattern of TnI expression (left panel), and loss of cTnI expression as ssTnIN141H replaces endogenous TnI (right panel). C. The pCa₅₀ at pH 7.0 (left panel), 6.2 (middle panel), and the shift in pCa₅₀ between pH 7.0 and 6.2 (right panel) for myofilament tension generation in myocytes expressing ssTnIN141H (n = 5) compared to cTnI- (control n = 8; cTnI n = 5) and ssTnI (n = 8) -expressing myocytes. Values are expressed as mean ± SEM and results were compared by a 1-way ANOVA and Tukey’s multiple comparison test, with *p<0.05 versus control and **p<0.05 for substitution mutant versus ssTnI. The pCa₅₀ in myocytes expressing ssTnIN141H is very similar to cTnI at pH 7.0, but the response to acidic pH more closely resembles the response observed in ssTnI-expressing myocytes.