P. Stewart

Protoplasmic movement in slime mold plasmodia: The diffusion drag force hypothesis

Abstract Cinephotomicrographic analyses of the vigorous protoplasmic movements in slime mold plasmodia have demonstrated the following facts. Flow at any point reverses direction with an irregular periodicity. Reversals in flow direction spread upstream or downstream along channels of flow. Movements at two points only a few microns apart may be independent in direction and reversal timing. At least three structural states of protoplasm are consistent with viability; state I, liquid, flowing; state II, non-flowing, elastic, but showing same Brownian movement as I; state III, elastic and more rigid than II, showing no Brownian movement. These three states are rapidly interconvertible, but flow only occurs in state I plus state II. The movements cannot be explained in terms of contraction of a gel posterior to the flow. They require a motive force which is distributed through the plasmodium in a pattern similar to that of the movement itself. The diffusion drag-force model of Rashevsky supplies such a motive force, and is consistent with the above data, as well as with extensive results of Kamiya and co-workers.

Membrane formation during sclerotization of Physarum polycephalum plasmodia

Abstract In the plasmodial slime molds, during the transition from the vegetative or plasmodial stage to the dormant sclerotial stage, a large increase in protoplast surface membrane occurs. Electron micrographic evidence is presented to suggest that this new surface arises from the fusion of already existing vesicles. Evidence for a similar process is available in many other organisms. All of these data seem to support the general concept of interconvertibility of biological membranes.

Effects of x-irradiation on muscle membrane.

Abstract X-irradiation on frog muscle in the range from 50 to 10,000 r did not produce early changes in the content of sodium or potassium, the permeability of the muscle membrane, ion fluxes, resting and action potentials, membrane resistance or membrane capacitance. This dose range of irradiation did not alter the relationship between resting membrane potential and temperature, nor that between resting membrane potential and external potassium ion concentration. Furthermore, the mechanical responses of frog muscle, such as contraction time, relaxation half time, twitch tension, maximal tetanus tension and optimal stimulus frequency were also unchanged by irradiation of 50 to 10,000 r. The temperature dependence of each of these parameters was studied in detail. On the other hand, preliminary studies now in progress suggested that higher doses (50,000 and 100,000 r) increased significantly the permeability of the muscle membrane to potassium ions.

Radiation damage in muscle cell membranes and regulation of cell metabolism.

Abstract : The study is concerned with the effect of x-radiation upon those properties and function of muscle cells. The research program was additionally extended to the study of cell membrane behaviour under the presence of cesium and quaternary ammonium ions, as well as to chemical damage studies with enzyme upon the molecular membrane structure. Unfortunately it was not possible to accomplish the proposed idea of studying the effects of x-radiation on the membrane mechanisms related to the Ach, Ch interaction, as well as the comparison of the radiation changes and the enzymatic alteration on the muscle membrane. The comparison between, mechanical, electrochemical, biochemical and structural changes in frog muscles following x-irradiation have contributed fundamentally to a basic understanding of the effects of irradiation on membrane system and control mechanism. Basically, the contribution was again oriented to obtain a better understanding of the effects of ionizing radiation in the sequence of processes taking place in the membrane and responsible for regulating the membrane potential as well as the membrane organization and function. Changes in the membrane permeability, and processes of membrane potential regulation, as well as in the processes related to uncoupling of oxidation and phosphorilation, due to radiation were considered an important observation of cell damage. (Author)

Irradiation and cesium depolarization of muscle membrane

Abstract Cesium ions in the bathing fluid produce a depolarization of frog sartorius muscle fibers independent of the depolarization produced by irradiation. The “fractional depolarization” produced by X-rays is independent of external cesium concentration. However, the “fractional depolarization” is proportional to external sodium concentration and is therefore explained as the result of an increased sodium ion permeability. Cesium depolarization (20 mMCs) in non-irradiated fibers increases with decreasing sodium concentration with osmolarity maintained by choline chloride, indicating a specific sodium-choline-cesium interaction in the membrane. A simple concentration-cell potential explanation for the cesium effects is not yet adequate.

ION EFFECTS IN X-RAY DEPOLARIZATION OF MUSCLE MEMBRANE.

Abstract Irradiation of frog sartorius muscles with 100 Kr of X-rays results in a relative decrease in resting membrane potential which is dependent on external sodium concentration, but not on potassium concentration provided that the latter exceeds 1.0 mM. In zero potassium solutions, the potential decreases more, and continues to fall after irradiation. Neither irradiation nor stimulation alters the rate at which 45Ca is lost from previously loaded muscle fibers. These results are interpreted to mean that irradiation damage to the muscle cell membrane results in increased permeability to sodium, but not via the release of calcium ions. The sodium extrusion mechanisms are altered by irradiation so as to require an external potassium concentration above 1.0 mM to match the increase of Na influx. Permeability to potassium does not appear to be altered by irradiation.

Transient Effects of Low-Level Microwave Irradiation on Bioelectric Muscle Cell Properties and on Water Permeability and Its Distribution

Microwave radiation effects on passive and dynamic electrical properties and on cell water parameters were studied in muscle cells from muscles of the South American Frog Leptodactilus ocellatus. Microwave exposure of 10 mW/cm2 for a period of 120 minutes produced transient changes in specific membrane resistance Rm, the membrane capacitance Cm and the space constant λ. Those electrical parameters related to the excitation and propagation of the action potential, i.e., the rate constants kr and kK, the maximum rate of rise v+ and fall v-of the action potential, the limiting membrane conductances (gNa and gK), the peaks of sodium inward and potassium outward ionic currents, the net ionic charge accumulation per action potential and the propagation velocity of the action potential, were all transiently altered. The water membrane permeability and the fraction of osmotically available cell volume were also transiently altered.

Radiation Effects on Water Permeability and Distribution in Frog Muscle Cells

Radiation effects on cell water parameters were analyzed in 400 single muscle fibers from tibialis anticus muscles of the South American frog Leptodactylus occelatus. Cell volume was calculated from cell diameter measured photomicrographically at 10-second intervals. Water permeability,

RADIATION AS AN UNCOUPLING AGENT IN FROG MUSCLE.

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Protoplasmic streaming and the fine structure of slime mold plasmodia

, and osmotically effective cell water,