Generation Of Action Potentials In Cells Research Articles

The Negative Chronotropic Effect of Cs+ Ions on Generation of Transmembrane Potentials in Mouse Sinoatrial Node Cells

Experiments on spontaneously contracting strips from sinoatrial region of the hearts of 2-month-old albino mice showed that cesium (Cs(+)), a blocker of hyperpolarization-activated I(f) current, in a concentration of 1 mM produced the greatest negative chronotropic effect on the duration of diastolic depolarization phase (75%), its rate (59%), and action potential duration (29%). The threshold concentration of Cs(+) was approximately 0.15 mM. In a concentration of about 8.5 mM, spontaneous generation of action potentials stopped. The effect was reversible. Thus, blockade of I(f) current by Cs(+) reduced the rate of action potential generation in cells of mouse sinoatrial node by app. 42% in comparison with controls.

Direct coupling of action potential generation in cells of a higher plant (Cucurbita pepo) with the operation of an electrogenic pump

Changes in membrane potential (Em) were investigated during action potential (AP) generation by excitable cells in bundle parenchyma of 2-week-old pumpkin (Cucurbita pepo L.) seedlings. APs were evoked by gradual cooling from 21 to 6°C at a rate of 1.3–1.5°C/min. Changes in Em were measured with standard microelectrode technique. The plots of the function dEm/dt = f (Em) were obtained from experimental data by numerical differentiation of Em records. The depolarization proceeded as a one-stage process. Conversely, AP repolarization comprised two stages, distinguished by specific dynamics of dEm/dt. The second stage of repolarization occurred on a larger scale of Em and was more sensitive to temperature than the first one. It is supposed that the second stage of repolarization during AP is related to the operation of electrogenic H+-pump in the excitable membrane. The scheme of AP generation in higher plant cells is suggested; it foresees the involvement in AP generation of both passive and active mechanisms of electrogenesis.