Effect of miconazole on the structure and function of plasma membrane of Candida albicans

Abstract

The primary mode of action of azoles is the inhibition of cytochrome P-450 dependent 14α-demethylase, a key enzyme in ergosterol biosynthesis in fungi. Our results demonstrated that Candida albicans cells grown in the presence of 10 µg ml⁻¹ of miconazole (miconazole-grown), do not possess ergosterol in their plasma membranes and this ergosterol depletion leads to a drastic change in membrane fluidity as shown by fluorescence polarization measurements and unsaturation index. There was an increase in membrane order in miconazole-grown cells and a reduced rate of uptake of amino acids. We also checked for membrane permeability changes in normal mid-log phase cells (normal-grown) in short incubations (10 min) with 10 µg ml⁻¹ miconazole (miconazole-incubated). Interestingly, the amino acid uptake rates except that Gly were not affected significantly in these cells. The results suggest that in the miconazole-incubated cells, the drug is not able to alter the level of ergosterol of inhibit ergosterol biosynthesis during 10 min incubation and therefore the interaction of the drug neither leads to significant disorganization of membrane components, nor affects permease activity, whereas in the miconazole-grown cells there is ergosterol depletion leading to accumulation of biosynthetic intermediates, resulting in membrane rearrangement thereby causing a major fluidity change. This fluidity change may explain the drastic reduction of amino acid transport in miconazole-grown cells. To investigate whether the reduction in amino acid transport was only due to change in membrane fluidity, as a consequence of absence of ergosterol, the PM-ATPase activity was checked in the miconazole-grown cells and was found to be unaffected, which suggests that changes in amino acid uptake were due to change in membrane fluidity.