Internal potassium activity in ferret ventricular muscle.

Area of Science:

• Cardiovascular Physiology
• Electrophysiology
• Ion Transport

Background:

• Intracellular potassium activity (aiK) is a critical determinant of cardiac cell function and electrophysiology.
• Accurate measurement of aiK is essential for understanding cardiac health and disease.
• Previous methods using standard K-sensitive micro-electrodes have shown limitations in cardiac tissue.

Purpose of the Study:

• To accurately measure intracellular potassium activity (aiK) in ferret ventricular myocytes.
• To compare the reliability of different micro-electrode sensors for aiK measurement.
• To evaluate the Nernst equation as an estimation method for aiK in cardiac tissue.

Main Methods:

• Intracellular potassium activity (aiK) was measured using single- and double-barrelled K-sensitive micro-electrodes.
• Two types of K sensors were tested: Corning K sensor and a valinomycin cocktail.
• aiK was also estimated using the Nernst equation by altering external K+ concentration and measuring membrane potential.

Main Results:

• Micro-electrodes with the Corning K sensor yielded unreliable aiK measurements, likely due to cellular interference.
• Reproducible and reliable aiK measurements were achieved using a valinomycin cocktail K sensor.
• The mean aiK measured with the valinomycin cocktail was 104 ± 9 mmol/l (strict criteria) or 101 ± 8 mmol/l (all experiments).
• Nernst equation estimations of aiK were consistently higher by approximately 20 mmol/l compared to valinomycin measurements.

Conclusions:

• A valinomycin cocktail-based micro-electrode is the recommended method for accurate aiK measurement in ferret ventricular tissue.
• Standard K-sensors may be prone to interference in cardiac cells, leading to inaccurate aiK readings.
• The Nernst equation provides a less accurate estimation of aiK compared to direct measurement with optimized micro-electrodes.