title: Magnesium and the calcium paradox: the occurrence of "spasmodic contractions" during Ca2+-Mg2+ -free perfusion of isolated rat heart.
abstract: The effects of omission of Mg2+ during Ca2+-free perfusion (3 min) of either spontaneously beating and electrically stimulated rat hearts were studied. Ca2+-free perfusion per se induced cardiac arrest and coronary vasodilation, and increased intrinsic pulse rate of the heart. Upon reperfusion with Ca2+, cardiac function was lost and parallelled by a sudden and massive release of cellular constituents ("calcium paradox"). Mg2+-free perfusion evoked effects opposite from Ca2+-free, with exception of heart rate which was increased. During Ca2+-Mg2+-free perfusion the electrocardiogram became irregular within 30 s, and this effect was followed by transient "spasmodic contractions". The effects of normal reperfusion were indistinguishable from those observed after Ca2+-free perfusion in the presence of Mg2+. Addition of Mn2+ or La3+ to the Ca2+-Mg2+-free perfusion medium completely inhibited the induction of electrical irregularities and spasmodic contractions. The typical effects of Ca2+-Mg2+-free perfusion are discussed in terms of Mg-Ca and Mg-K interactions at the sarcolemmal surface. It was concluded that our results may contribute indirectly to an explanation of the protective effect of high Mg2+-concentrations during Ca2+-free as well as ischemic perfusion of mammalian hearts.
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D002304:Cardiac Pacing, Artificial; D003331:Coronary Vessels / Q000187:drug effects; D003864:Depression, Chemical; D004562:Electrocardiography; D006321:Heart / Q000187:drug effects; D006323:Heart Arrest / Q000139:chemically induced; D007473:Ion Channels / Q000502:physiology; D008274:Magnesium / Q000502:physiology*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D010477:Perfusion; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D007473:Ion Channels; D008274:Magnesium; D002118:Calcium