The effect of potassium on the electrocardiogram: clinical and transmembrane correlations.

A KNOWLEDGE OF MOLECULAR BIOLOGY in health and disease has been a goal of the modern-day physician. Until recently , understanding of the electrocardio-gram has been based mostly on the sequence and duration of the myocardial activation process. The introduction of the Lmg-Gerard1 microcapillary electrode has permitted a study of the resting and action potential of an individual cell. Consequently , the bases for understanding of the elec-trocardiogram can be re-evaluated by studying the events occurring at the trans-membrane cellular level during depolariza-tion and repolarization. The interior of the resting cell in skeletal, nerve and cardiac tissue is negative with regard to the exterior. What are the factors responsible for the membrane resting potential (MRP) and the membrane action potential (MAP)? Based largely on the study of the squid giant axon, Hodg-kin5 demonstrated that polarization of the cell depends largely on the ionic concentrations of sodium and potassium inside and outside the cell. These lOfliC Concentrations produce an electromotive force which can be calculated and understood from the Nernst equation: E== ln [[ [ ] According to this equation, the potential is directly proportional to the gas constant R, absolute temperature T, and inversely proportional to the Faraday F and propor-*From the Division of Medicine, Cedars-Sinai Medical Center. tional to ln (natural log) times the ratio of the ionic concentration inside (i) and outside (o) the cell.