Temperature effect on isometric tension is mediated by regulatory proteins tropomyosin and troponin in bovine myocardium

The effect of temperature on isometric tension with and without the regulatory proteins tropomyosin and troponin was studied in bovine myocardium using a thin filament removal and reconstitution protocol. In control bovine myocardium, isometric tension increased linearly with temperature in the range 5-40 degrees C: isometric tension at 10 and 30 degrees C was 0.65 and 1.28 times that at 20 degrees C, respectively, with a Q10 of about 1.4. In actin filament-reconstituted myocardium without regulatory proteins, the temperature effect on isometric tension was less: isometric tension at 10 and 30 degrees C was 0.96 and 1.17 times that at 20 degrees C, respectively, with a Q10 of about 1.1. The temperature dependence of the apparent rate constants was studied using sinusoidal analysis. The temperature dependence of 2pi(b) (rate constant of delayed tension phase) did not vary significantly with the regulatory proteins under the standard activating condition (5 mM MgATP, 8 mM P(i), 200 mM ionic strength, pCa 4.66, pH 7.00). Q10 for 2pi(b) in control and actin filament-reconstituted myocardium was 3.8 and 4.0, respectively. There were two phases to the temperature dependence of 2pi(c) (rate constant of quick recovery). In control and thin filament-reconstituted myocardium, Q10 for 2pi(c) was approximately 5.5 in the low temperature range (< or = 25 degrees C) and 2.7 in the high temperature range (> or = 30 degrees C). In actin filament-reconstituted myocardium, Q10 for 2pi(c) was 8.5 in the low temperature range and 3.6 in the high temperature range. The above results demonstrate that regulatory proteins augment the temperature dependence of isometric tension, indicating that the regulatory proteins may modify the actomyosin interaction.