Modeling gender effects on electrical activity of single ventricular myocytes

The effect on the sarcolemmal Na(+)-K+ pump of exposure to anisosmolar solutions was examined using whole cell patch clamping and ion-selective microelectrodes. Na(+)-K+ pump currents were measured in single ventricular myocytes by using pipette Na+ concentrations ([Na]pip) of 0-70 mM. The relationship between [Na]pip and pump current was well described by the Hill equation. The [Na]pip for half-maximal pump current (K0.5) was 21.4 mM in isosmolar (310 mosM) solution. K0.5 was 12.8 mM during cell swelling in hyposmolar solution (240 mosM) and 39.0 mM during cell shrinkage in hyperosmolar solution (464 mosM). The maximal pump currents, derived from the best fit of the Hill equation, and the Hill coefficients were similar in isosmolar, hyposmolar, and hyperosmolar solutions. A sustained (> 20 min) decrease in the intracellular Na+ activity developed during exposure of intact papillary muscles to hyposmolar solutions, and a sustained increase developed during exposure to hyperosmolar solutions. We conclude that osmotic myocyte swelling stimulates the sarcolemmal Na(+)-K+ pump at near-physiological levels of intracellular Na+, whereas shrinkage inhibits the pump. These changes are due to increases and decreases, respectively, in the apparent affinity of the pump for Na+.

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Effect of reduced Na gradient on electrical activity in isolated bovine and feline ventricular myocytes

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y88-038 ◽

1988 ◽

Vol 66 (2) ◽

pp. 222-232 ◽

Cited By ~ 1

Author(s):

Magda Horackova ◽

Andrzej Beresewicz ◽

Gerrit Isenberg

Keyword(s):

Electrical Activity ◽

Ventricular Myocytes ◽

Ionic Current ◽

Outward Current ◽

Free Solution ◽

Initial Part ◽

Inward Current ◽

Ca Inward Current ◽

Sudden Decrease ◽

K Currents

We have studied changes in electrical activity resulting from abrupt alterations of the Na gradient, using ventricular myocytes isolated from feline and bovine hearts. Attempting to investigate the ionic current possibly generated by Na–Ca exchange, we studied the effects of the changes in [Na]o in the presence of 20 mM CsCl to inhibit K currents. To facilitate the effect of Cs, we also used a K-free solution and a patch electrode filled with 150 mM cesium glutamate. The application of 20 mM Nao resulted in hyperpolarization and the action potential duration was reduced. Under voltage clamp, 20 or 45 mM Nao generated an outward current at all membrane potentials investigated. The initial part (100–200 ms) of this current was only partially inhibited by 5 mM NiCl2 which is known to fully block the Ca inward current. However, the outward current generated by the reduced [Na]o was fully inhibited by 20 mM MnCl2 (which presumably inhibits Na–Ca exchange). Our observations extend the work on multicellular cardiac preparations indicating that the outward current elicited by a sudden decrease in Na gradient could be generated by Na–Ca exchange. Although the characteristics of this outward current support certain concepts of the Na–Ca exchange in cardiac muscle, we cannot at present exclude a contribution of other membrane current(s).

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