Abstract
CYCLOSTOME branchial hearts are known to contain large amounts of endogenous catecholamines1 and to be markedly insensitive to added adrenaline2,3. There is considerable evidence to suggest that the process whereby the sympathomimetic amines normally enhance the force of cardiac contraction involves the transformation of the enzyme phosphorylase from the b to the a form4,5. The lack of sensitivity of cyclostome hearts to added adrenaline or noradrenaline might therefore be due to the endogenous amines having already activated the conversion of the phosphorylase enzyme from the b to the a form so that even in the absence of any added adrenaline or noradrenaline the enzyme phosphorylase would exist mainly in the a form. This possibility was investigated using hearts isolated from freshly decapitated lampreys (Mordacia). After five minutes immersion in aerated (95 per cent O2 + 5 per cent CO2) modified Ringer solution6 at 22° C, under which conditions isolated hearts will beat spontaneously for many hours, the hearts were rapidly frozen and the phosphorylase activity determined as described previously7, using tissue dilutions of 1/150 (w/v) and rabbit liver glycogen (Nutritional Biochem. Lab.) which had been purified as described by Krebs et al.8. The reaction mixture was incubated at 25° C.
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NAYLER, W., HOWELLS, J. Phosphorylase a/b Ratio in the Lamprey Heart. Nature 207, 81 (1965). https://doi.org/10.1038/207081a0
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DOI: https://doi.org/10.1038/207081a0
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