The effect of extracellular potassium on the intracellular potassium ion activity and transmembrane potentials of beating canine cardiac purkinje fibers

Abstract

We used open tip microelectrodes containing a K+-sensitive liquid ion exchanger to determine directly the intracellular K+ activity in beating canine cardiac Purkinje fibers. For preparations superfused with Tyrode’s solution in which the K+ concentration was 4.0 mM, intracellular K+ activity (aKi) was 130.0 ± 2.3 mM (mean ± SE) at 37°C. The calculated K+ equilibrium potential (EK) was - 100.6 ± 0.5 mV. Maximum diastolic potential (ED) and resting transmembrane potential (Em) were measured with conventional microelectrodes filled with 3 M KCl and were -90.6 ± 0.3 and -84.4 ± 0.4 mV, respectively. When [K+]o was decreased to 2.0 mM or increased to 6.0, 10.0, and 16.0 mM, aKi remained the same. At [K+]o = 2.0, ED was -97.3 ± 0.4 and Em -86.0 ± 0.7 mV; at [K+]o = 16.0, ED fell to -53.8 ± 0.4 mV and Em to the same value. Over this range of values for [K+]o, EK changed from -119.0 ± 0.3 to -63.6 ± 0.2 mV. These values for EK are consistent with those previously estimated indirectly by other techniques. © 1977, Rockefeller University Press., All rights reserved.