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

Hideaki Fujita and Masataka Kawai

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 °C: isometric tension at 10 and 30 °C was 0.65 and 1.28 times that at 20 °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 °C was 0.96 and 1.17 times that at 20 °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 2b (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 2b in control and actin filament-reconstituted myocardium was 3.8 and 4.0, respectively. There were two phases to the temperature dependence of 2c (rate constant of quick recovery). In control and thin filament-reconstituted myocardium, Q₁₀ for 2c was approximately 5.5 in the low temperature range (≤ 25 °C) and 2.7 in the high temperature range (≥ 30 °C). In actin filament-reconstituted myocardium, Q₁₀ for 2c 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.

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