[Active exchange of Na and K in perfused and procaine arrested rat heart]

Recovery of normal Na and K contents of perfused and procaine arrested rat ventricules occurs with a rate constant of 0.109 mn-1 (i.e. 60% of restoration is achieved in 7.5 mn) after a 45 mn arrest of active transport produced by perfusion with a K free Krebs-Henseleit solution. Active Na efflux is nearly equal to K influx. Peak Na Efflux is estimated to be 11.2 muEq.g-1dry.mn-1 or 19.7 pM.cm-2.s-1, i.e. more than 4 times leakage flux of the resting heart. Na efflux is not proportional to Na intracellular concentration but to the square of this concentration.