Consequences of impeding in mitochondrial function in Physarum polycephalum. I. Reversible effects of anoxia, KCN, and influences of the Ca2+ ionophore A-23187.

5 mM KCN as well as anoxia have corresponding effects on Physarum plasmodia: Both induce a disintegration of the plasmalemma invaginations, an increase in cytoplasmic vacuoles, formation of a thick cortical actomyosin layer and an increase of cytoplasmic actomyosin fibrils. Both KCN treatment and anoxia cause a temporary increase in the level of the force oscillations and a reversible prolongation of the periods of the contraction-relaxation cycle of cytoplasmic actomyosin. The normal pattern of oscillation can be restored by the addition of 10 mM alpha-ketoglutarate +5 mM AMP to the solution containing 5 mM KCN. A combination of the Ca2+ ionophore A-23187 and KCN induces a strong contracture, whereas a combination of KCN, ionophore, alpha-ketoglutarate and AMP prevents this effect. The state of contracture is characterised by a pronounced increase in the Young's modulus and an increased fibrillogenesis of cytoplasmic actomyosin. The isometrically contracted state during the high force output represents a strict parallel arrangement of F-actin. The capability of alpha-ketoglutarate in combination with AMP to restore the normal pattern of oscillation as well as to inhibit contractures is interpreted as a stimulation of the alternate pathway of respiration. It is suggested that this stimulation leads to a restoration of cellular Ca2+-homeostasis originally disturbed by the impediment of cell respiration.