Altering extracellular potassium concentration from 2.0 to 16.0 mM in canine cardiac Purkinje fibers did not change intracellular K+ activity (130.0+/-2.3 mM), while K+ equilibrium potential changed.
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 (ak) was 130.0+/-2.3 mM (mean+/-SE) at 37 degrees 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, ak 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.
Miura et al. (Fri,) conducted a other in Beating canine cardiac Purkinje fibers. Extracellular potassium concentration changes vs. 4.0 mM was evaluated on Intracellular K+ activity and transmembrane potentials. Altering extracellular potassium concentration from 2.0 to 16.0 mM in canine cardiac Purkinje fibers did not change intracellular K+ activity (130.0+/-2.3 mM), while K+ equilibrium potential changed.