The effect of temperature on Na currents in rat myelinated nerve fibres
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Voltage clamp experiments were performed in single myelinated nerve fibres of the rat and the effect of temperature on Na currents was investigated between 0°C and 40°C.
The amplitude of the peak Na current changed with aQ 10=1.1 between 40° and 20°C and with aQ 10=1.3 between 20° and 10°C. Below 10°C the peak Na current changed with aQ 10=1.9.
The temperature coefficient for time-to-peak (tp), the measure for Na activation, and τh1 and τh2, the time constants for Na inactivation changed throughout the temperature range.Q 10 for all of these kinetic parameters increased from 1.8–2.1 between 40° and 20°C to 2.6–2.7 between 20° and 10°C. Below 10°CQ 10 increased to 3.7 for τh1 and tp, and to 2.9 for τh2. When the series resistance artifacts were minimized by addition of 6 nM TTX, theQ 10's atT<10°C were 2.9–3.0.
When the temperature was decreased from 20° to 0°C, both the curve relating Na permeability to potential,P Na(V), and the steady state Na inactivation curve,h∞(V), were reversibly shifted towards more negative potentials by 6 mV and 11 mV, respectively. When the temperature was increased from 20° to 37°C no shifts occurred.
The Hodgkin-Huxley rate constants αh(V) and βh(V) were calculated fromh ∞(V) and τh (or τh1) at 20° and 4°C. The shift inh∞(V) and the change inh ∞(V), which occurred within this temperature range, could be described assuming a selective shift in τh(V) along the potential axis.
Key wordsNode of Ranvier Rat nerve Na current Temperature dependence Voltage clamp
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