Temperature effects on Ca2+ cycling in scombrid cardiomyocytes: A phylogenetic comparison

Abstract

Specialisations in excitation-contraction coupling may have played an important role in the evolution of endothermy and high cardiac performance in scombrid fishes. We examined aspects of Ca2+ handling in cardiomyocytes from Pacific bonito (Sarda chiliensis), Pacific mackerel (Scomber japonicus), yellowfin tuna (Thunnus albacares) and Pacific bluefin tuna (Thunnus orientalis). The whole-cell voltage-clamp technique was used to measure the temperature sensitivity of the L-type Ca2+ channel current (ica), density, and steady-state and maximal sarcoplasmic reticulum (SR) Ca 2+ content (ssSRload and maxSRload). Current-voltage relations, peak ica density and charge density of ica were greatest in mackerel and yellowfin at all temperatures tested. ica density and kinetics were temperature sensitive in all species studied, and the magnitude of this response was not related to the thermal preference of the species. SRload was greater in atrial than in ventricular myocytes in the Pacific bluefin tuna, and in species that are more cold tolerant (bluefin tuna and mackerel). ica and SRload were particularly small in bonito, suggesting the Na+/Ca2+ exchanger plays a more pivotal role in Ca2+ entry into cardiomyocytes of this species. Our comparative approach reveals that the SR of cold-tolerant scombrid fishes has a greater capacity for Ca2+ storage. This specialisation may contribute to the temperature tolerance and thermal niche expansion of the bluefin tuna and mackerel. © 2011. Published by The Company of Biologists Ltd.