Stimulation of Strontium Accumulation in Linoleate-Enriched Saccharomyces cerevisiae Is a Result of Reduced Sr 2+ Efflux

Abstract

ABSTRACT 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 ∼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 μM 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 following 18:2-enrichment, which is attributed to diminished Sr 2+ efflux activity in these cells.