Primary oscillator of contractional rhythm in the plasmodium of Physarum polycephalum: Role of mitochondria.

Abstract

Various inhibitors were microinjected into the cytoplasm of the plasmodium of Physarum polycephalum, and their effects were monitored by measurements of contractile activity, and the intracellular ATP and cytoplasm-ic Ca2+ concentrations. Fluoride and monoiodoacetate (glycolytic inhibitors) reduced the ATP by 50 %, but the contractional rhythm was unaffected. In contrast, azide and arsenate (respiratory inhibitors) and 2, 4-dinitrophenol (uncoupler) induced a transient decrease of 50 % in the ATP value and a 2-3-fold transient prolongation of the rhythm. A combined injection of glycolytic and respiratory inhibitors reduced the ATP to 10 % and led to complete ces-sation of the rhythm. P-chloromercuribenzoate (SH-blocking reagent) had similar effects as those of a respiratory inhibitor, but N-ethylmaleimide had no affect. Ruthenium red (inhibitor of mitochondrial Ca2+-uptake) did not affect the ATP value, but did bring about gradual prolongation of the rhythm accompanying an increase in the Ca2+ efflux into the cytoplasm.These results are evidence that the time-keeping of contractional rhythm inPhysarum plasmodium is related primarily to mitochondrial activity.