[Regulatory role of monoamine neurotransmitters in Saccharomyces cerevisiae cells].

Proliferation of Saccharomyces cerevisiae EPF cells on solid maltose-peptone-yeast extract (MPY) medium was stimulated by the addition of monoamine neurotransmitters. Dopamine turned out to be the most efficient among them: it caused approximately 8-fold growth stimulation at 1 microM concentration. The dopamine effect was partly mimicked by apomorphine, a dopamine receptor agonist. Serotonin and histamine produced less significant (1.5-2-fold) effects, and norepinephrine virtually failed to stimulate yeast culture growth. These data point to a specific, apparently receptor-dependent mode of action of the tested neurotransmitters on S. cerevisiae cells. Using high efficiency liquid chromatography, serotonin, catecholamines (dopamine and norepinephrine), catecholamines precursor dioxyphenylamine, and oxidized amine products (homovanilic acid, dihydrophenylacetic acid, and 5-hydroxyindolacetic acid) were established to be accumulated in yeast cells up to (sub)micromolar concentrations without their release into the culture fluid supernatant (CSF). The results obtained suggest that the tested amine neurotransmitters and related compounds do not serve as autoregulators in the yeast population. Nevertheless, they may be involved in the regulation of yeast population development by other ecosystem components.

[Effects of monoamine neuromediators on the growth-related variables of Escherichia coli K-12].

The monoamine neuromediators serotonin (5-HT), histamine, dopamine (DA), and norepinephrine (NE), added to an Escherichia coli K-12 strain MC 4100 culture upon inoculation, stimulate cell proliferation (determined from CFU formation) and biomass accumulation (monitored nephelometrically) during the late lag phase and the early exponential growth phase. These effects are less significant in the late exponential and stationary phase cultures. According to the concentration dependence of the stimulatory effects, the neuromediators can be classified into two groups: (i) the catecholamines DA and NE, whose effects increase almost linearly with increasing concentrations within the range of 0.1-100 microM, and (ii) histamine and 5-HT, which are characterized by bell-shaped concentration dependence curves with maxima at 0.1 (histamine) and 1 microM (5-HT). On an agar-containing medium, the growing E. coli population includes solitary cells and compact cell groups (microcolonies). In this system, both tested catecholamines exert a relatively weak stimulatory influence that manifests itself as an increase in the number of both solitary cells and cell groups, and occurs at concentrations of 10 microM and higher. In analogy to the culture grown on the liquid medium, 5-HT and histamine are distinguished by nonlinear concentration dependence curves: their effects peak at 0.1 microM (histamine) or 1 microM (5-HT); an increase in the neuromediator concentrations results in a decrease in effects that are enhanced by further increasing the concentrations to the submillimolar range. DA increases the percentage of solitary cells, whereas the other tested amines promote cell group formation. The results are interpreted in terms of specific (probably receptor-dependent) mechanisms of action of the neuromediators involved.