Temperature-dependence of isometric tension and cross-bridge kinetics of cardiac muscle fibers reconstituted with a tropomyosin internal deletion mutant

Abstract

The effect of temperature on isometric tension and cross-bridge kinetics was studied with a tropomyosin (Tm) internal deletion mutant AS-Δ23Tm (Ala-Ser-Tm Δ(47-123)) in bovine cardiac muscle fibers by using the thin filament extraction and reconstitution technique. The results are compared with those from actin reconstituted alone, cardiac muscle-derived control acetyl-Tm, and recombinant control AS-Tm. In all four reconstituted muscle groups, isometric tension and stiffness increased linearly with temperature in the range 5-40°C for fibers activated in the presence of saturating ATP and Ca 2+. The slopes of the temperature-tension plots of the two controls were very similar, whereas the slope derived from fibers with actin alone had ∼40% the control value, and the slope from mutant Tm had ∼36% the control value. Sinusoidal analysis was performed to study the temperature dependence of cross-bridge kinetics. All three exponential processes A, B, and C were identified in the high temperature range (30-40°C); only processes B and C were identified in the mid-temperature range (15-25°C), and only process C was identified in the low temperature range (5-10°C). At a given temperature, similar apparent rate constants (2πa, 2πb, 2πc) were observed in all four muscle groups, whereas their magnitudes were markedly less in the order of AS-Δ23Tm < Actin