Aims: 

Hypokalemia is a common clinical condition, and is associated with increased risk of ventricular tachyarrhythmias and sudden cardiac death. Our aim was to study how low extra-cellular potassium affected Ca²⁺ transients, and to investigate whether this affected Ca²⁺ wave probability.

Methods: 

Rat cardiomyocytes were isolated, loaded with fluo-4, and field stimulated on 1, 2 and 4 Hz. Ca²⁺ transients were measured with fluorescensce microscopy. The stimulation was temporarily stopped for 30 seconds between each increase in stimulation frequency, and Ca2+ waves were observed. The protocol was performed with [K⁺]e=2.7 mM and [K⁺]e=5.0 mM.

Results: 

Upon switch in perfusion from basal (2.7 mM) to low extracellular potassium (5.0 mM), the Ca²⁺ transients increase through a biphasic response; a rapid decline (p< 0.05 compared to basal), followed by a slower increase in Ca²⁺ transients. A stable phase was reached after a few minutes, where the Ca²⁺ transients were increased compared with transients on basal potassium (p< 0.05). We also observed increased wave occurrence on low extracellular potassium compared with basal perfusion on all frequencies studied (p< 0.05).

Conclusion: 

Low extracellular potassium increases Ca²⁺ wave probability, and increases Ca²⁺ transients through a biphasic response. This might be an arrhythmogenic mechanism in hypokalemia.