Amiodarone-mediated increase in intracellular free Ca²⁺ associated with cellular injury to human pulmonary artery endothelial cells

The cardiac antidysrrhythmic drug amiodarone can give rise to potentially fatal pulmonary toxicity in large numbers of patients. The effect of amiodarone on Ca²⁺ homeostasis and cell injury has been studied using human pulmonary artery endothelia (HPAE) cells in vitro. Amiodarone produced a concentration-dependent increase in intracellular free Ca²⁺ concentration ([Ca²⁺]_i) to micromolar levels that are similar to those seen with physiological stimuli that increase [Ca²⁺]_i. Unlike physiological stimuli, the rise in [Ca²⁺]_i produced by amiodarone developed slowly and was maintained over at least 30 min. Omitting Ca²⁺ from the external medium reversibly prevented the amiodarone-induced rise in [Ca²⁺]_i. Amiodarone treatment increased the apparent first order rate constants for ⁴⁵Ca²⁺ influx and efflux in intact HPAE cells. ⁴⁵Ca²⁺ accumulation into the endoplasmic reticulum of saponin-permeabilized HPAE cells was decreased by amiodarone treatment. The release of ⁴⁵Ca²⁺ from the endoplasmic stores by the putative intracellular second messengers inositol-1,4,5-trisphosphate, arachidonic acid, and Ca²⁺ was blocked by amiodarone treatment. The changes in Ca²⁺ homeostasis coincide with an increase in [³H]deoxyglucose release as a measure of early cell injury by amiodarone. It is concluded that amiodarone can produce an increase in [Ca²⁺]_i by an action on the plasma membrane that allows the influx of external Ca²⁺. This increase in [Ca²⁺]_i, together with other changes in Ca²⁺ homeostasis, may be responsible for the early cell injury associated with amiodarone toxicity.