Nitric oxide plays a role in the regulation of adrenal blood flow and adrenocorticomedullary functions in the llama fetus

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 Q ₁₀ 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 Q ₁₀ of about 1.1. The temperature dependence of the apparent rate constants was studied using sinusoidal analysis. The temperature dependence of 2π b (rate constant of delayed tension phase) did not vary significantly with the regulatory proteins under the standard activating condition (5 m m MgATP, 8 m m P_i, 200 m m ionic strength, pCa 4.66, pH 7.00). Q ₁₀ for 2π b in control and actin filament-reconstituted myocardium was 3.8 and 4.0, respectively. There were two phases to the temperature dependence of 2π c (rate constant of quick recovery). In control and thin filament-reconstituted myocardium, Q ₁₀ for 2π c 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, Q ₁₀ for 2π 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.