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.
