Calculation of Q10 and activation energy (Ea)

As described by Steffens et al., 2008³³ the voltage pulse protocol was used: starting at a constant holding potential of −80 mV voltages from −100 mV to + 60 mV were applied for 20 s in steps of 20 mV. 5 s after returning to holding potential of − 80 mV a post pulse to − 100 mV for 5 s followed before returning to the holding potential of −80 mV. Between two test pulses, a 30-s resting phase at the holding potential was followed. I₂₀ denotes the interval at the end of the 20-s conditioning voltage pulses where the amplitude of the evoked currents measured (I₂₀). I₁₀ denotes the interval at the end of the 10-s conditioning voltage pulses where the amplitude of the evoked currents measured (I₁₀).

Q₁₀ is used to describe the temperature dependence of a process. It is a unit less temperature coefficient and is a measure of the rate of change of a biological or chemical system as a consequence of increasing the temperature by 10 °C. Q₁₀ calculations were performed by Q₁₀ = (R₂/R₁)^10 °C/(T₂^-T₁⁾; with R₁ is the rate which represent the ion flux in µA after 20 s at temperature T₁ in Celsius degrees, whereas the rate R₂ is obtained at the higher temperature T₂.

The activation energy (E_a), was calculated from linear slopes from semi logarithm plot using normalized currents vs temperature 1/T⁶². Therefore normalized currents at I₂₀ were obtained and the calculations were performed according to I₂₀ = A e^−Ea/RT; with current at 20 s (I₂₀) Arrhenius constant A activation energy E_a (kJ/mole), R the gas constant (8.31447 J/mole K) and T temperature (K).