Action of barium and potassium ions on fluctuations of the myocyte membrane potential in the rat papillary muscle

: Using a common microelectrode technique membrane potential fluctuations (MPF) have been studied in experiments on the papillary muscles of rat cardiomyocytes. Parallel measurements of oscillations in resting tension (mechanical noise--MN) from the muscle ends were performed. A correlation between MPF and MN was absent in the control. After the addition of barium (0.2 mM) MPF increased, assumed a sinusoidal form and synchronized with MN. Membrane depolarization evoked by external current resulted in a similar effect. However, the depolarization induced by a high potassium dose (30 mM) was accompanied by MPF and MN decrease. The opposite effects of barium and potassium on MPF might be a result of their different influences on the muscle length constant (which is increased by Ba2+ and decreased by K+).