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  • Title: Absence of calcium paradox in the cardiac ventricle of the Atlantic hagfish (Myxine glutinosa).
    Author: Poupa O, Ask JA, Helle KB.
    Journal: Comp Biochem Physiol A Comp Physiol; 1984; 78(1):181-3. PubMed ID: 6146433.
    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+.
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