Effects of beauvericin on the metabolic state and ionic homeostasis of ventricular myocytes of the guinea pig.

Beauvericin, a cyclic hexadepsipeptide with antibiotic properties, has been shown to reduce contraction force and to affect action potential parameters of guinea pig papillary muscles. Its potential to form cation-selective channels in mammalian membranes has been demonstrated. Patch clamp and fluorescence imaging techniques were used to investigate its effects in enzymatically isolated ventricular myocytes. Application of 10 microM beauvericin caused a large [Ca2+]i increase in Fura 2AM-loaded cardiomyocytes leading to cell shortening. The effect could be partially inhibited by ryanodine pretreatment and was largely dependent on external Ca2+ and blocked by 5 mM Ni2+. Beauvericin initiated a progressive increase in [Mg2+]i, the time course of which developed similarly upon increasing the external chemical gradient of Mg2+ 10-fold, to produce an ionophoric challenge. Monitoring of pH(i) with BCECF showed that beauvericin caused cytosolic acidification. Confocal microscopy revealed mitochondrial depolarization in TMRM-loaded cardiomyocytes, which resembled the effect of classical mitochondrial uncouplers. However, the NADH autofluorescence signal followed a biphasic pattern, in contrast to the NADH response to the uncouplers FCCP and the K+-ionophore valinomycin. These results suggest that beauvericin, possibly via its ionophoric properties, acts as an atypical mitochondrial uncoupler, greatly disturbs the physiological ionic balance and pH, challenges cellular metabolism, and causes ATP depletion.