Fungicidal activity of amiodarone is tightly coupled to calcium influx

The antiarrhythmic drug amiodarone has microbicidal activity against fungi, bacteria and protozoa. In Saccharomyces cerevisiae, amiodarone triggers an immediate burst of cytosolic Ca²⁺, followed by cell death markers. Ca²⁺ transients are a common response to many forms of environmental insults and toxic compounds, including osmotic and pH shock, endoplasmic reticulum stress, and high levels of mating pheromone. Downstream signaling events involving calmodulin, calcineurin and the transcription factor Crz1 are critical in mediating cell survival in response to stress. In this study we asked whether amiodarone induced Ca²⁺ influx was beneficial, toxic or a bystander effect unrelated to the fungicidal effect of the drug. We show that downregulation of Ca²⁺ channel activity in stationary phase cells correlates with increased resistance to amiodarone. In actively growing cells, extracellular Ca²⁺ modulated the size and shape of the Ca ²⁺ transient and directly influenced amiodarone toxicity. Paradoxically, protection was achieved both by removal of external Ca ²⁺ or by adding high levels of CaCl₂ (10 mM) to block the drug induced Ca²⁺ burst. Our results support a model in which the fungicidal activity of amiodarone is mediated by Ca²⁺ stress, and highlight the pathway of Ca²⁺ mediated cell death as a promising target for antifungal drug development.