Kinetics of release of amino acids by Leishmania major

When Leishmania promastigotes are exposed to a sudden decrease in osmolality, they initially swell but subsequently undergo compensatory shrinkage by a regulatory volume decrease (RVD) response. The associated mechanism involves anionic amino acid channels (termed HAAC for hypotonic-activated amino acid anion channel) which allow neutral and acidic amino acids to be released from the cells. The HAAC(s) system(s) operates in a manner analogous to volume activated anion channels that mediate the efflux of small organic osmolytes in several mammalian cells. A large body of evidence suggests that the level of protein phosphorylation/dephosphorylation regulates the activity of several transporters that mediate the volume regulatory responses of a wide variety of cells. To ascertain whether a similar type of regulatory mechanism regulates the hypotonic-induced amino acid release in Leishmania parasites, Vieira et al. assessed the effect of a number of selected agonists and antagonists of protein kinases and phosphatases on the kinetics of amino acid release in response to a decrease in osmolality from isotonicity (300 mOsm) to 150 mOsm.