Intracellular and extracellular magnesium concentration-dependent alteration of electrical excitability in cardiac myocytes

Abstract

[Background] Regulation of intracellular and extracellular free magnesium (Mg²⁺) concentration is important to control the excitability in cardiac myocytes. [Objective] To assess the role of intracellular and extracellular Mg²⁺ imbalance in cardiac myocytes associated with membrane potentials and ionic currents derangement. [Methods and Results] Serum and intracellular Mg²⁺ concentrations were measured from normal (control) and the Mg²⁺ -deficient food feeded rats. The serum [Mg²⁺]e and intracellular Mg²⁺ concentrations [Mg²⁺]i were significantly decreased from 6.9 ± 0.3 mg/dl and 2.3 ± 0.2 mg/dl to 4.4 ± 0.2 mg/dl and 0.7 ± 0.1 mg/dl on Mg²⁺ -deficient diet on day 28, respectively. We obtained ECG signals by a radio transmitter from control and the Mg²⁺-deficient rats. Low [Mg²⁺]e significantly prolonged RR duration (control, 181 ± 17 ms versus low [Mg²⁺]e, 158 ± 18 ms, p < 0.05) in accordance with various types of cardiac arrhythmias such as supraventricular extrasystole, atrioventricular blocks and so on. Action potentials (AP) from rat ventricle myocytes were recorded by using intracellular microelectrode technique. AP durations (APD₉₀) in myocytes obtained from Mg²⁺ -deficient rats were significantly prolonged (control, 101.2 ± 3.2 ms versus low-Mg²⁺, 314.0 ± 11.8 ms, p < 0.01). [Conclusion] Decreases in intracellular and extracellular Mg²⁺ concentrations cooperatively contribute toward arrhythmogenecity presumably affecting intracellular Ca²⁺ concentrations. [J Physiol Sci. 2006;56 Suppl:S128]