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Magnesium affects excitation, conduction, and contraction of isolated mammalian cardiac muscle

Hall, Sarah K. and Fry, C. H. 1992. Magnesium affects excitation, conduction, and contraction of isolated mammalian cardiac muscle. American Journal of Physiology - Heart and Circulatory Physiology 263 (2) , H622-H633.

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An increase of extracellular Mg concentration, [Mg]o, reduced myocardial excitability and conduction without affecting the resting membrane potential or action potential configuration in ventricular myocytes and papillary muscles from a number of mammalian species. Although there was a small increase of specific membrane resistance and no change to intracellular resistivity, the threshold voltage was shifted to depolarized potentials. Thus loss of excitability can be explained by a shift of the activation of inward currents to depolarized potentials, and reduced conduction velocity is due solely to a diminution of local circuit currents. Mgo also was negatively inotropic, the magnitude of this effect being species dependent. Raised [Mg]o caused a small increase of intracellular [Mg] with a small decrease of intracellular [Na+], did not affect intracellular pH, and attenuated the intracellular Ca2+ transient associated with cell shortening in rat (but not rabbit) myocytes. An increase of [Mg]o reduced the magnitude of the voltage-dependent inward Ca2+ current, ICa, in rat and rabbit myocytes, and the activation curve of ICa was shifted to more depolarized potentials. A scheme to account for the negative inotropic effect of Mg is presented.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Biosciences
Subjects: Q Science > QP Physiology
Publisher: American Physiological Society
Last Modified: 04 Jun 2017 07:53

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