Effects of acute warming on cardiac and myotomal sarco(endo)plasmic reticulum ATPase (SERCA) of thermally acclimated brown trout (Salmo trutta)

Matti Vornanen

doi:10.1007/s00360-020-01313-1

Matti Vornanen

Open Access

https://doi.org/10.1007/s00360-020-01313-1

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Abstract

At high temperatures, ventricular beating rate collapses and depresses cardiac output in fish. The role of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) in thermal tolerance of ventricular function was examined in brown trout (Salmo trutta) by measuring heart SERCA and comparing it to that of the dorsolateral myotomal muscle. Activity of SERCA was measured from crude homogenates of cold-acclimated (+ 3 °C, c.a.) and warm-acclimated (+ 13 °C, w.a.) brown trout as cyclopiazonic acid (20 µM) sensitive Ca2+-ATPase between + 3 and + 33 °C. Activity of the heart SERCA was significantly higher in c.a. than w.a. trout and increased strongly between + 3 and + 23 °C with linear Arrhenius plots but started to plateau between + 23 and + 33 °C in both acclimation groups. The rate of thermal inactivation of the heart SERCA at + 35 °C was similar in c.a. and w.a. fish. Activity of the muscle SERCA was less temperature dependent and more heat resistant than that of the heart SERCA and showed linear Arrhenius plots between + 3 and + 33 °C in both c.a. and w.a. fish. SERCA activity of the c.a. muscle was slightly higher than that of w.a. muscle. The rate of thermal inactivation at + 40 °C was similar for both c.a. and w.a. muscle SERCA at + 40 °C. Although the heart SERCA is more sensitive to high temperatures than the muscle SERCA, it is unlikely to be a limiting factor for heart rate, because its heat tolerance, unlike that of the ventricular beating rate, was not changed by temperature acclimation.

Highlights

Sarcoplasmic reticulum (SR) functions as an intracellular Ca2+ store in striated muscle cells and regulates the rate of rise and fall of intracellular C a2+-transient in excitation–contraction (e-c) coupling (Fabiato 1983; Rossi and Dirksen 2006; Periasamy and Kalyanasundaram 2007)
At pH values higher than 7.2, the activities declined in almost liner manner with slight differences between heart and muscle sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA)
The respective time constants of inactivation for the muscle SERCA were 7.77 ± 1.36 and 9.56 ± 0.79 min for c.a. and w.a. trout, respectively (Mann–Whitney, p = 0.16) (Fig. 4b). These analyses show that there is no difference in the rate of thermal inactivation between c.a. and w.a. trout either for muscle or heart SERCA

Summary

Introduction

Sarcoplasmic reticulum (SR) functions as an intracellular Ca2+ store in striated muscle cells and regulates the rate of rise and fall of intracellular C a2+-transient in excitation–contraction (e-c) coupling (Fabiato 1983; Rossi and Dirksen 2006; Periasamy and Kalyanasundaram 2007). The lumenal SR C a2+ content must be replenished after each contraction to maintain proper efficacy of SR C a2+ release, which is critically dependent on SR C a2+ load Sequestration of cytosolic C a2+ back into the SR is accomplished by the sarco(endo)plasmic reticulum Ca2+-ATPase or SERCA. The heart gene codes for three functionally different splice variants, SERCA2a/b/c, and the muscle gene two SERCA1a/b splice variants (Thomas and Hanley 1994; Londraville et al 2000; Wuytack et al 2002; Periasamy and Kalyanasundaram 2007)

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