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Is potassium conductance of cardiac Purkinje fibres controlled by [Ca2+]i?


ELEVATED extracellular Ca2+ concentration1, prolonged treatment with high doses of cardiac glycosides2, and metabolic inhibition3 shorten the action potential of cardiac muscle. In these conditions the intracellular free Ca2+ may be increased and an increase in intracellular Ca2+ could produce shortening of the action potential either by affecting the Ca2+ inward current or by increasing the potassium permeability4. The latter mechanism has been observed in red blood cells5 and in the neurones of some species6–8. Here I give the results of studying the effect of iontophoretically injected Ca2+ in cardiac Purkinje cells. Such injection led to membrane hyperpolarisation and considerable shortening of the action potential, suggesting that the level of intracellular free Ca2+ can affect the potassium permeability in cardiac muscle.

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ISENBERG, G. Is potassium conductance of cardiac Purkinje fibres controlled by [Ca2+]i?. Nature 253, 273–274 (1975).

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