The effect of extracellular Mg<sup>2+</sup> on action potential in guinea pig papillary muscles

Chang, Sung-Eun; Kim, Shang-Jin; Kang, Hyung-Sub; Kim, Jin-Shang

Korean Journal of Veterinary Research 2003;43(1):31-39.

The effect of extracellular Mg²⁺ on action potential in guinea pig papillary muscles

Sung-Eun Chang, Shang-Jin Kim, Hyung-Sub Kang, Jin-Shang Kim

Bio-Safety Research Institute, Chonbuk National University

기니픽 심장 유두근에서 magnesium이 활동전위에 미치는 영향

장성은, 김상진, 강형섭, 김진상

전북대학교 생체안전성연구소

Abstract

We have investigated the effect of extracellular $Mg^{2+}$ ($[Mg^2+]_o$) on action potential duration (APD) in guinea pig papillary muscles by using microelectrodes. Increasing $[Mg^2+]_o$ resulted in progressive negative inotropic effect, progressive ascending depolarization of membrane potential, and increase in intracellular $Mg^{2+}$ concentration. In addition, increase in $[Mg^2+]_o$ from 1.1 to 3, 6, 10, and 20 mM produced a reversible dose-dependent shortening of both APD at 30% ($APD_{30}$) and 90% repolarization ($APD_{90}$), especially showing a tendency towards more remarkable prominent shortening in $APD_{30}$ than $APD_{90}$. Cooling from 37 to 33 and $27^{circ}C$ diminished the $[Mg^2+]_o$-induced APD shortening. Increase in extracellular $Ca^{2+}$ concentration from 1.8 to 3.6 and 5.4 mM caused a significant depressed effect on the increasing $[Mg^2+]_o$-induced APD shortening. Furthermore, increase in $[Mg^2+]_o$ from 1.1 to 10 and 20 mM produced a significant depressed effect on the APD shortening induced by extracellular $Ca^{2+}$. Pretreatment of verapamil and imipramine significantly attenuated the increasing $[Mg^2+]_o$-induced APD shortening in both $APD_{30}$ and $APD_{90}$, whereas the $[Mg^2+]_o$-induced APD shortening was not affected by strophanthidin, glibenclamide and tetrabutylammonium. These findings suggest that the effects of $[Mg^2+]_o$ on APD are probably due to a decrease in ionic transport across plasma membrane. In conclusion, the present study indicates that $[Mg^2+]_o$ exerts antiarrhythmic activities by antagonistic actions on intracellular $Ca^{2+}$.

Key Words: magnesium, calcium, action potential duration, temperature, intracellular $Mg^{2+}$