Abstract
Background: Intracellular and extracellular magnesium (Mg2+) plays a important role to control the excitability in cardiac myocytes. Objective: To assess the effects of low magnesium diet on rat heart associated with action potentials (AP), ionic currents and expression of mRNA focusing on the K+ channels in cardiac myocytes. Methods and Result: Serum and intracellular Mg2+ concentrations were measured from normal (control) and the magnesium-deficient food feeded rats (hypomagnesium rat). ECG in hypomagnesium rat shows significantly shorter R-R intervals (control, 180.3 ± 6.1 ms vs hypomagnesium 146.8 ± 6.8 ms, p<0.05). Action potential duration (APD) in ventricular myocytes were recorded by intracellular microelectrode. APD90 in myocytes obtained from hypomagnesium rats were significantly prolonged (control, 101.2 ± 3.2 ms vs hypomagnesium, 314 ± 11.8 ms, p<0.05). Inward-rectifier K+ current (IK1) obtained by whole-cell patch clamp method indicates a decrease in IK1 density and it's conductance in myocytes from hypomagnesium rat. Expression of Kir2.1 mRNA was significantly downregulated by 38.5 ± 4.2% in myocytes derived from hypomagnesium rat, while expression of Kir2.2 mRNA was unchanged. Conclusion: These results suggest that intracellular and extracellular magnesium ion modifies the inward-rectifier K+ current, Kir2.1 in particular, by means of channel kinetics and expression. [J Physiol Sci. 2007;57 Suppl:S207]
