Longjaw mudsuckers tune heart to temperature

Abstract

Sitting in our nice warm bodies, it can be hard to appreciate the challenges faced by animals that live in environments with constantly fluctuating temperature, but one of the problems experienced by ectothermic animals is how to keep their hearts going across a wide range of temperatures. Nishad Jayasundara from Duke University, USA, explains that longjaw mudsuckers (Gillichthys mirabilis) reside along the Eastern Pacific coast from the cool northern Tomales Bay to the sizzling Baja peninsula in the south. While studying at Stanford, he wondered how the hearts of these animals adjust to life at 9, 19 and 26°C, so Jayasundara and his colleagues Lars Tomanek from California Polytechnic State University, USA, Wesley Dowd from Loyola Marymount University, USA, and George Somero from Stanford University, USA, decided to find out how the protein composition of the fish's hearts changed at the different temperatures.Collecting the hearts of fish that had been acclimated to each of the three temperatures for 4 weeks, the team found 122 proteins that changed in abundance using 2D gel electrophoresis, 37 of which were identified using mass spectrometry. Cataloguing the functions of the 37 proteins, the team found that almost half (48%) are involved in energy metabolism, five are involved in cytoskeletal structure, three contribute to protein degradation and transport and two are associated with iron homeostasis. Focusing on the responses that are essential for survival at a cellular level at each temperature, the team found that the 19°C-acclimated fish had increased levels of proteins that are necessary for ATP production, while the hottest fish had reduced levels of the same proteins. Meanwhile, the coldest fish had an increased abundance of creatine kinase, an enzyme that is essential for energy supply to muscle fibres, and the hottest and coldest fish had increased levels of a protein called hexosaminidase, which has a role in stress protection.The team says, ‘The capacity to adjust ATP-generating processes is crucial to the thermal plasticity of cardiac function’, and concludes that the mudsuckers optimise their cellular function at 19°C, which is within the range of temperatures at which they seem most comfortable.