Permeability of Dictyostelium discoideum towards Amino Acids and Inulin: a Possible Relationship between Initiation of Differentiation and Loss of 'Pool' Metabolites

Abstract

The permeability of Dictyostelium discoideum amoebae towards amino acids and inulin was studied under conditions suitable for development of aggregationcompetence and in thick cell suspensions. During the pre-aggregation period, the amoebae released large amounts of amino acids and nucleotides into the suspending medium. The uptake of glutamate and lysine by amoebae was passive, but inulin was taken up actively, probably by pinocytosis. Hence the simplest explanation for leakage of metabolites is that the amoebae have no active mechanism for retaining them. A possible relationship between initiation of differentiation and loss of pool metabolites is discussed.

Solute Uptake by Dictyostelium discoideum and its Inhibition

“…1) in agreement with the findings of Lee (1972). This labelling was inhibited completely by 0.1 mM-dinitrophenol and 1 mM-sodium azide.…”

“…In the experiments reported here, solute uptake rates were measured in suspensions of myxamoebae starved in sodium phosphate buffer, a system used in some previous studies on uptake in D. discoideum (Lee, 1972;North & Williams, 1978;Turner et al, 1979). Although this system is one in which uptake may not be of major physiological importance (the myxamoebae are not feeding at this stage), it has the advantage over the use of suspensions of growing cells in that it avoids complex media whose precise composition, including concentrations of factors which might influence uptake rates, could vary from one experiment to another.…”

Relationship Between the Axenic Phenotype and Sensitivity to -Aminocarboxylic Acids in Dictyostelium discoideum

“…A similar effect to that of sodium azide was observed with 0.1 mM-dinitrophenol. The effects of cycloheximide and dinitrophenol differed from those reported by Lee (1972) on lysine uptake by AX^ myxamoebae. However, our own observations indicate that the uptake of lysine is inhibited by cycloheximide, dinitrophenol and sodium azide (M. J.…”

“…The uptake of EACA by D. discoideum is unlike that observed with rabbit retina which can accumulate EACA at concentrations above that in the medium (Ehinger, 1976), but is similar to the uptake of other amino acids by D. discoideum (Lee, 1972;M. J.…”

The effect of AMP on the NAD-dependent glutamate dehydrogenase during activation and morphogenesis in the cellular slime moulds

“…D. discoideum is a free-living phagotrophic soil organism that feeds on bacteria and divides by binary fission. The cue to begin development in the asexual cycle is the depletion of its bacterial food source or amino acid starvation (Lee, 1972;Marin, 1976Marin, , 1977Darmon & Klein, 1978;Margolskee et al, 1980). Founder or initiator cells begin secreting cAMP in pulses (Sussman, 1956;Bonner, 1957;Ennis & Sussman, 1958) to which the surrounding amoebae are attracted.…”