Effects of seasonal acclimatization on thermal tolerance of inward currents in roach (Rutilus rutilus) cardiac myocytes

To test the hypothesis of temperature-dependent deterioration of electrical excitability (TDEE) (Vornanen, J Exp Biol 219:1941–1952, 2016 ), the role of sodium ( I Na ) and calcium ( I Ca ) currents in heat tolerance of cardiac excitability was examined in a eurythermic fish, the roach ( Rutilus rutilus ). Densities of cardiac I Ca and I Na and their acute heat tolerance were measured in winter-acclimatized (WiR) and summer-acclimatized (SuR) fish maintained in the laboratory at 4 ± 1 and 18 ± 1 °C, respectively. A robust L-type Ca 2+ current ( I CaL ), but no T-type Ca 2+ current, was present in roach atrial and ventricular myocytes. Peak density of I CaL was smaller in atrial (− 1.97 ± 0.14 and − 1.75 ± 0.19 pA/pF for WiR and SuR, respectively) than ventricular myocytes (− 4.00 ± 0.59 and − 2.88 ± 0.47 pA/pF for WiR and SuR, respectively) ( p