title: Absence of calcium paradox in the cardiac ventricle of the Atlantic hagfish (Myxine glutinosa).
abstract: Spontaneously beating strips of the cardiac ventricle of the cyclostome Myxine glutinosa were characterized with respect to dependence on extracellular calcium for the cardiac contractility at 8 degrees C. The force developing (Tmax) was reduced by 20-50% when exposed to calcium-free medium (+/- 10(-3)M EDTA) for 15-60 min. Return to normal Myxine Ringer (4.5 mM Ca2+) resulted in 120-130% recovery to Tmax without change in resting tension. These experiments show that the heart of this primitive vertebrate, analogous to that of other poikilotherms, does not display the "Ca-paradox" phenomenon. Being relatively insensitive to changes in extracellular Ca2+ the Myxine myocardium differs from that in most poikilotherms in other respects, e.g. in the mechanisms regulating beat to beat changes in intracellular Ca2+.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004492:Edetic Acid / Q000494:pharmacology; D005399:Fishes / Q000378:metabolism*; D006196:Hagfishes / Q000378:metabolism*; D006321:Heart / Q000502:physiology; D006352:Heart Ventricles; D007473:Ion Channels / Q000378:metabolism*; D007552:Isotonic Solutions / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D000077331:Ringer's Solution
chemical_list: D007473:Ion Channels; D007552:Isotonic Solutions; D000077331:Ringer's Solution; D004492:Edetic Acid; D002118:Calcium