Ion Diffusion Delay in the Beating Mammalian Heart. ∗

Abstract

Summary

Rates of washout of Na²⁴⁺ and I¹³¹were measured in the working perfused guinea pig heart in vitro at 37° and 25°C. Washout occurred at 2 or more rates with at least 80% of the ions comprising the fast component and exchanging at a mean rate of 1.03 min^-1. There were no significant differences between the washout rates of the Na²⁴⁺ and I^131- at the 2 temperatures studied. Washout of tissue slices 400-500 μ thick occurred at a single rate one-tenth that of the fast component in the working perfused heart. The data indicate that ion diffusion delay in passing through the extracellular spaces does not play a significant role in evaluation of K transfer in this preparation, and they also support previous findings that the fast component of K exchange does not represent extracellular localization.