The plasmodium of Physarum polycephalum reacts to various kinds of chemical substances and moves towards or away from them. Threshold concentration of recognition of chemicals was examined in terms of membrane potential and of the averaged motive force of tactic movement by using a double-chamber method, i.e., a single plasmodium was placed between two compartments through a narrow ditch, and differences in membrane potential and in pressure between two compartments were measured. Results are summarized as follows: (a) By increasing the concentration of various substances in one compartment, the membrane potential started to change at a certain threshold concentration, Cth, for each chemical. Chemotactic movement of the plasmodium took place at the same threshold concentration. These results held both for attractants (glucose, galactose, phosphates, pyrophosphates, ATP, c-AMP, etc.) and for repellents (various inorganic salts, sucrose, fructose, etc.). (b)The threshold concentration, Cth, for inorganic salts decreased remarkably with increase of the valences of cations, z, and was proportional to z -'6, i.e., the Shultze-Hardy rule known in the field of colloid chemistry was found to be applicable. (c) The plasmodium distinguished the species of monovalent cations in the following order: H(Li(K(Na(Rb(Cs(NH4. Plots of log Cth against the lyotropic number of anion fell on different straight lines for each monovalent cation species. (d) Plots of log Ct~ against the reciprocal of the absolute temperature followed different straight lines for different substances. The slopes of the lines were almost the same and gave a value of 12 kcal/mol for the enthalpy change. These results suggest that the recognition of chemical substances appears as the result of a structural change of the membrane at the threshold point, and that the change in membrane structure is transmitted simultaneously to the motile system of the plasmodium.
: The anemia frequently observed in lead poisoning is thought to result from the shortening of erythrocyte life span in combination with inhibition of hemoglobin synthesis.However, the exact mechanism by which lead shortens the life span of red blood cells (RBCs) remains unclear. In the present study, the effects of injected lead on electrophoretic mobility, membrane sialic acid content, deformability and survival of rat RBCs were investigated in order to clarify the relationships between them. As indices of lead exposure, RBC counts, hemoglobin (Hb) levels, hematocrits (Ht), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC) and blood lead (blood Pb) levels in the rats were also examined. Exposure to lead significantly decreased RBC counts, Hb levels, Ht, MCV and MCH. Similarly, exposure to lead significantly decreased the mobility, sialic acid content and deformability of rat RBCs. A shortening of erythrocyte survival time was also observed in the rats exposed to lead. It is speculated that decreases in membrane sialic acid content and deformability of RBCs induce a shortening of erythrocyte survival time in anemia caused by lead.
Interaction between salt and sugar receptions in plasmodium of Physarum polycephalum was studied by using double-chamber method. Effect of sugars on salt reception was evaluated by measuring membrane potential and the motive force of tactic movement of the slime mold, where salt concentration in one compartment was increased successively with a fixed sugar concentration. Results are summarized as follows: (1) The presence of D-glucose, D-mannose, D-maltose, or sucrose in medium led to increase of the threshold concentration Cth, for salts (chlorides and nitrates of Li, Na, K), whereas D-ribose decreased the threshold for salt reception. D-galactose showed no appreciable effect on Cth of every salt species examined. No change in Cth for salt reception was observed until concentration of sugars exceeded their respective thresholds. (2) Double logarithmic plots of Cth for salts against sugar concentration followed different straight lines for different cations, whose slopes being closely correlated with the effects of lyotropic number of anions in the absence of sugars. (3) Plots of log Cth against the reciprocal of the absolute temperature, 1/T, gave linear relations, and the slopes of the straight line became small with increase of sugar concentration above their respective thresholds. Experimental results obtained here suggest that the structure of water at the interface of cell membrane plays an indispensable role in the interaction between salt and sugar receptions.
Treatment of Klebsiella pneumoniae 109 with cefodizime, ceftazidime, cefbuperazone, cefotaxime or flomoxef at a sub-minimum inhibitory concentration (sub-MIC) (1/4 MIC) for 1 h altered its morphology. The bacteria treated with cefodizime at sub-MICs (1/8, 1/4 MIC) enhanced the chemiluminescencence (CL) of human polymorphonuclear leucocytes (PMNs), implying an increase in the production of active oxygen species in association with phagocytosis, whereas the cells treated with other cephalosporins at the same sub-MICs did not. Furthermore, a significant decrease in electrophoretic mobility was induced by the bacteria treated with cefodizime at sub-MICs (1/8, 1/4 MIC), but other cephalosporins neither increased nor decreased the electrophoretic mobility significantly. These findings suggested that cefodizime caused a morphological change, with a decrease in negative surface charge density of K. pneumoniae, more easily than ceftazidime, cefbuperazone, cefotaxime or flomoxef, followed by an increase in the phagocytic activity of PMNs.
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