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Quantitation of Na/Ca exchanger function in single ventricular myocytes.
Z Su1, J H Bridge, K D Philipson
1Division of Cardiology, University of Utah Health Sciences Center, Salt Lake City, Utah 84132, USA.
Journal of Molecular and Cellular Cardiology
|May 25, 1999
Summary
Researchers measured sodium-calcium exchange current in mouse heart cells. Overexpressing the sodium-calcium exchanger significantly increased this current, offering a new method to study exchanger function.
Area of Science:
- Cardiovascular Physiology
- Molecular Cardiology
- Ion Transport
Background:
- The sodium-calcium exchanger (NCX) plays a critical role in regulating intracellular calcium levels in cardiomyocytes.
- Understanding NCX function is vital for comprehending cardiac electrophysiology and calcium homeostasis.
- Previous studies have relied on indirect methods to assess NCX activity.
Purpose of the Study:
- To directly measure the reverse sodium-calcium exchange current in isolated ventricular myocytes.
- To characterize the properties of this current and its dependence on intracellular and extracellular sodium concentrations.
- To evaluate the utility of this method in quantifying changes in NCX activity, particularly in genetically modified models and across species.
Main Methods:
- Utilized voltage-clamped single ventricular myocytes isolated from wild-type and NCX-overexpressing transgenic mice.
- Employed a rapid-perfusion system to induce reverse Na/Ca exchange current by abrupt removal of extracellular Na+.
- Measured current sensitivity to nickel, intracellular Na+ removal, and ouabain; manipulated pipette Na+ concentration to assess current magnitude.
Main Results:
- Successfully elicited and measured a robust reverse Na/Ca exchange current in mouse ventricular myocytes.
- Demonstrated that the current is nickel-sensitive, eliminated by intracellular Na+ removal, and not contaminated by Na+ pump currents.
- Observed a significant 2.5-2.7 fold increase in Na/Ca exchange current in transgenic myocytes overexpressing NCX, correlating with previous uptake studies.
- Reported species-specific variations in exchanger current densities (mouse>rat>rabbit>dog>human).
Conclusions:
- Direct measurement of Na/Ca exchange current in single myocytes is feasible and provides a sensitive assay for NCX function.
- NCX overexpression substantially enhances reverse Na/Ca exchange current, validating the experimental approach.
- This technique offers a valuable tool for investigating NCX alterations in disease states and drug development.