Entrainment to external Ca2+ oscillation in ionophore-treated Physarum plasmodium.

To elucidate the mechanism of mutual interaction between intracellular chemical rhythms in the Physarum plasmodium, external Ca2+ oscillation was applied to the ionophore-treated plasmodial strand and its response was measured as tension oscillation. (i) Tension oscillation is entrained and phase locked to the externally applied Ca2+ oscillation. (ii) Two kinds of stable phase relationship, in-phasic and anti-phasic ones, are observed between them. (iii) Transition between the two stable phase relationships is also observed. These results suggest that intracellular rhythms with control tension generation are mutually entrained by means of cytosolic Ca2+ oscillation in the organism and that their interactions have two kinds of stable phase relationships.