Contractile elements of Lemna trisulca L. glycerinated cell models during chloroplast translocations.

Electron microscopy of Lemna glycerinated cell models depicts contractile elements during chloroplast translocations. One contractile element, the thin ectoplasmic layer, is < or = 0.4 microm thick, pressed against plasma membrane-cell wall. Thin ectoplasmic layer contains numerous oriented filaments and some appear to be actin and myosin. Another contractile element is the outer chloroplast membrane which envelops each chloroplast and joins or fuses with the thin ectoplasmic layer. Chloroplast interconnections are formed between two or more chloroplasts by outer chloroplast membranes; they enhance chloroplast communications, translocations, and molecular exchanges.

Electrical resistivity of a tumor.

The resistivities of a Swarm murine basement membrane sarcoma and also surrounding tissue in BALB/c mice were determined. The circuit used allowed resistivity to be measured independently of the electrode geometry and capacitance. The tumor exhibited a resistivity of 310 +/- 52 omega X cm and the tissue 653 +/- 142 omega X cm.

Oriented thick and thin filaments in Amoeba proteus.

Actin and myosin filaments as a foundation of contractile systems are well established from ameba to man (3). Wolpert et al. (19) isolated by differential centrifugation from Amoeba proteus a motile fraction composed of filaments which moved upon the addition of ATP. Actin filaments are found in amebas (1, 12, 13) which react with vertebrate heavy meromyosin (HMM), forming arrowhead complexes as vertebrate actin (3, 9), and are prominent within the ectoplasmic tube where some of them are attached to the plasmalemma (1, 12). Thick and thin filaments possessing the morphological characteristics of myosin and actin have been obtained from isolated ameba cytoplasm (18, 19). In addition, there are filaments exhibiting ATPase activity in amebas which react with actin (12, 16, 17). However, giant ameba (Chaos-proteus) shapes are difficult to preserve, and the excellent contributions referred to above are limited by visible distortions occurring in the amebas (rounding up, pseudopods disappearing, and cellular organelles swelling) upon fixation. Achievement of normal ameboid shape in recent glycerination work (15) led us to attempt other electron microscope fixation techniques, resulting in a surprising preservation of A. proteus with a unique orientation of thick and thin filaments in the ectoplasmic region.

On electrical condution in living bone.

Despite the effectiveness of electrical currents in enhancing bone repair, there is little information in the literature on electrical parameters per se. Very little is known about the nature of the conduction mechanism or the current path between the electrodes. Without a better understanding it is difficult to establish meaningful hypotheses at the cellular level and to design relevant experimental protocols. In the present work, a first attempt is made at an in vivo delineation of the current-voltage relationship in the medullary area between two platinum electrodes embedded in the femur, by one of the techniques generally known to stimulate bone growth. At potential differences of less than 1 volt, a rather good ohmic dependence is observed, with an approximate specific resistance of 2 to 5 times 10-5 ohms/cm. At potentials higher than 1 volt, electrolytic processes appear to predominate and there is increasing non-linearity. Experimental techniques involving the adjustment of current through bone tissue assuming an ohmic dependence with little or no associated polarization effects are valid and certainly warrant further investigation.