Repetitive stimulation at 2-4 Hz in guinea-pig papillary muscle increased intracellular sodium and extracellular potassium, while post-stimulation hyperpolarization was largely explained by extracellular potassium depletion.
Does repetitive stimulation alter intra- and extracellular potassium and intracellular sodium activities and membrane potential in guinea-pig papillary muscle?
In guinea-pig papillary muscle, hyperpolarization following repetitive stimulation is primarily driven by extracellular potassium depletion due to Na-K pump activity rather than an electrogenic component.
We measured changes in membrane potential (MP), extra- and intracellular potassium and intracellular sodium ion activities (aKo, aKi, and aNai) in papillary muscle of the guinea-pig heart induced by repetitive stimulation at various frequencies and periods in vitro, using double-barrelled ion-selective microelectrodes. Stimulation (2-4 Hz) depolarized the cells, and termination of stimulation induced hyperpolarization. The aKi and aNai (stimulated at 0.2 Hz) were 92.3 +/- 4.6 and 7.8 +/- 2.0 mM (mean +/- S.D.), respectively. Prolongation of the stimulation period (0.5-2 min) increased aNai time-dependently, but there was no further increase by stimulation for longer than 3 min. The increase in aNai was dependent on stimulus frequency. After termination of the stimulation aiNa declined exponentially. aKi slightly decreased by the stimulation (3-4 Hz). aKo increased during the stimulation period, and decreased below the initial level after termination of the stimulation. Results suggest that in guinea-pig papillary muscle, the contribution of an electrogenic component of Na-K pump to the hyperpolarization after stimulation would be small, since the hyperpolarization could be explained mostly by depletion of aKo induced by Na-K pump activity.
Hotokebuchi et al. (Thu,) conducted a other in Normal cardiac electrophysiology (guinea-pig papillary muscle). Repetitive electrical stimulation vs. Low frequency stimulation (0.1-0.2 Hz) was evaluated on Changes in membrane potential and intracellular sodium/potassium activities. Repetitive stimulation at 2-4 Hz in guinea-pig papillary muscle increased intracellular sodium and extracellular potassium, while post-stimulation hyperpolarization was largely explained by extracellular potassium depletion.