Effects of caffeine and D2O on persistence and de novo generation of intrinsic oscillatory contraction automaticity in Physarum.

The present investigation was performed in an attempt to contribute to answering the question whether the plasmalemma of the plasmodial stage of Physarum represents the site of a trigger mechanism for the oscillating contraction activity of cytoplasmic actomyosin. The effects of the following substances on persistence of tensiometrically measured longitudinal and radial activities of Physarum veins and on de novo generation of activities in experimentally generated drops were studied: caffeine, theophylline, acetylcholinium chloride, procaine, physostigminium salicylate, iso-ompa, nifedipin, sodium nitroprusside, potassium thiocyanate, D2O; as well as the effects of ions such as La+++ and high outer concentrations of Na+ and K+. Some of the substances were applied simultaneously for comparison externally (by bathing solutions) and internally (by injection). The experimental data speak against the existence of electrogenic rhythmical Ca++, Na+ or K+ pumps across the plasmalemma which could have a triggering function for the oscillation. The contraction activities of the cytoplasmic actomyosin seem to represent a spontaneous endogeneous oscillation which can be modulated via the plasmalemma during chemotaxis.