An analysis of calcium-magnesium antagonism in contractility and ionic balance in isolated trabecular muscle of rat ventricle

Publisher Website
Google Scholar
Abstract
The influence of elevated Mg (20 mM) on mechanical response, fibre electrolyte composition and Ca-exchange, as a function of external Ca concentration, has been studied in an isolated trabecular muscle column of rat ventricle. At [Ca]0 2.5 mM, cellular Mg-content increased in 20 mM [Mg]0 without effect on contractility or fibre content of other electrolytes. As [Ca]0 was reduced from 2.5 mM, 20 mM Mg caused progressive inhibition of contractile response of muscle to electrical stimulation. In both resting and stimulated trabeculae the intrafibre Mg-content rapidly increased and Ca-content fell in the initial 20 min incubation in reduced (1.5 or 0.75 mM) Ca, as the contractile response declined. Subsequent restoration of [Ca]0 to 2.5 mM restored contractile response in the presence of high Mg concentration. Exposure of trabeculae to high Mg also caused a significant decrease in 45-Ca exchange in a muscle calcium-pool exchanging witht1/2 7 min when [Ca]0 was 1.5 mM, but had no effect on Ca-exchange when [Ca]0 was 2.5 mM. The effect of high Mg on exchange of Ca indicated that displacement of a fraction of superficially-bound muscle Ca was responsible for the diminished contractile response in Mg-loaded trabeculae.