Temperature dependent properties of sodium inward current of frog atrial trabecles

From frog atrial trabecles sodium inward current in dependence on temperature was investigated using a double sucrose gap technique. For a first period of cooling the Arrhenius plot of time constants of activation and inactivation and peak current time tp show a break near 5 degrees C that is not detectable for the data of the succeeding period of rewarming. For the second and third cooling period the extreme delay of currents failed indicating an irreversible change of membrane structure after a temperature cycle. Rewarming always causes hysteresis of tp whose genuiness is proven by comparison of currents of temperature jump and ramp.