Stimulation of strontium accumulation in linoleate-enriched Saccharomyces cerevisiae is a result of reduced Sr2+ efflux

The influence of modified plasma membrane fatty acid composition on cellular strontium accumulation in Saccharomyces cerevisiae was investigated. Growth of S. cerevisiae in the presence of 1 mM linoleate (18:2) (which results in 18:2 incorporation to approximately 70% of total cellular and plasma membrane fatty acids, with no effect on growth rate) yielded cells that accumulated Sr(2+) intracellularly at approximately twice the rate of S. cerevisiae grown without a fatty acid supplement. This effect was evident over a wide range of external Sr(2+) concentrations (25 micromolar to 5 mM) and increased with the extent of cellular 18:2 incorporation. Stimulation of Sr(2+) accumulation was not evident following enrichment of S. cerevisiae with either palmitoleate (16:1), linolenate (18:3) (n-3 and n-6 isomers), or eicosadienoate (20:2) (n-6 and n-9 isomers). Competition experiments revealed that Ca(2+)- and Mg(2+)-induced inhibition of Sr(2+) accumulation did not differ between unsupplemented and 18:2-supplemented cells. Treatment with trifluoperazine (TFP) (which can act as a calmodulin antagonist and Ca(2+)-ATPase inhibitor), at a low concentration that precluded nonspecific K(+) efflux, increased intracellular Sr(2+) accumulation by approximately 3.6- and 1.4-fold in unsupplemented and 18:2-supplemented cells, respectively. Thus, TFP abolished the enhanced Sr(2+) accumulation ability of 18:2-supplemented cells. Moreover, the rate of Sr(2+) release from Sr(2+)-loaded fatty acid-unsupplemented cells was found to be at least twice as great as that from Sr(2+)-loaded 18:2-enriched cells. The influence of enrichment with other fatty acids on Sr(2+) efflux was variable. The results reveal an enhanced Sr(2+) accumulation ability of S. cerevisiae 18:2-enrichment, which is attributed to diminished Sr(2+) efflux activity in these cells.