Abstract. An hypothesis considering mitochondria as intracellular power-transmitting protonic cables was tested in human fibroblasts where mitochondria are thin and long and in rat cardiomyocytes where they show cluster organization. Mitochondria in the cell were specifically stained with fluorescent-penetrating cation ethylrhodamine, which electrophoretically accumulates in the mitochondrial matrix.A 40-1xm-long mitochondrial filament of fibroblast was illuminated by a very narrow (~0.5 ~tm) laser beam to induce local damage of the mitochondrial membranes. Such a treatment was found to induce quenching of the ethylrhodamine fluorescence in the entire filament. According to the electron microscope examination, the laser-treated filament retained its continuity after the laser illumination. Other mitochondrial filaments (some of which were localized at a distance <10 ~tm from the laser-treated one) remained fluorescent. In a cell where mitochondrial filaments seemed to be united in a network, laser illumination of one filament resulted in fluorescence quenching in the whole network, whereas fluorescence of small mitochondria not connected with the network was unaffected.The illumination of cardiomyocyte was found to result in the fluorescence quenching not only in a laserilluminated mitochondrion but also in a large cluster of organeUes composed of many mitochondria. Electron microscopy showed that all the mitochondria in the cluster change from the orthodox to the condensed state. It was also found that mitochondria in the cluster are connected to one another with specific junctions. If a mitochondrion did not form junctions with a quenched cluster, its fluorescence was not decreased even when this mitochondrion was localized close to an illuminated one. The size of the mitochondrial cluster may be as long as 50 lam. The cluster is formed by branched chains of contacting mitochondria, which may be defined as Streptio mitochondriale. In the cardiomyocyte there are several mitochondrial clusters or, alternatively, the quenched cluster is a result of decomposition of a supercluster uniting all the mitochondria of the cell. Cluster organization of mitochondria could also be revealed when a single mitochondrion was punctured in situ with a microcapillary. The obtained data are in agreement with the idea that mitochondrial junctions are H ÷ permeable so that, within the cluster, A~ may be transmitted from one mitochondrion to another.The above results are consistent with the assumption that mitochondrial filaments or networks represent a united electrical system. (Possible functions of extended mitochondrial systems are discussed.) M EMBRANE structures containing energy-releasing and energy-consuming enzymes are defined as coupling membranes. If within one membrane there are a AIiH-generating respiratory chain and an H ÷-ATP synthase, respiration and phosphorylation can be coupled via A~H (19). It is obvious that both A~ and ApH constituents of AIiH, once they are formed across it, immediately spread along the membran...

The dynamics of mitotic chromosome and interphase chromatin recondensation in living PK cells during their adaptation to hypotonic medium was studied. The recondensation process was found to be slowed down by the modification of plasma membrane with low concentrations of glutaraldehyde, while osmotic reactions of glutaraldehyde-treated cells remain unchanged. The effect of glutaraldehyde can be rapidly reversed by the addition of Ca 2+ -ionophore A23187. Intracellular Ca 2+ measurements show that the adaptation to hypotonic shock is accompanied by restoration of free Ca concentration, whereas the delay of chromatin condensation in glutaraldehyde-treated cells is paralleled by the decrease of Ca level. The mechanisms implying the role of low concentration of Ca 2+ in chromatin compactization in vivo are discussed.