- 1Pentamidine, an antiprotozoal agent, has been traditionally known to cause QT prolongation and arrhythmias; however, its ionic mechanism has not been illustrated.
- 2In a stable HEK-293 cell line, we observed a concentration-dependent inhibition of the hERG current with an IC50 of 252 μM.
- 3In freshly isolated guinea-pig ventricular myocytes, pentamidine showed no effect on the L-type calcium current at concentrations up to 300 μM, with a slight prolongation of the action potential duration at this concentration.
- 4Since the effective concentrations of pentamidine on the hERG channel and APD were much higher than clinically relevant exposures (∼1 μM free or lower), we speculated that this drug might not prolong the QT interval through direct inhibition of IKr channel. We therefore incubated hERG-HEK cells in 1 and 10 μM pentamidine-containing media (supplemented with 10% serum) for 48 h, and examined the hERG current densities in the vehicle control and pentamidine-treated cells.
- 5In all, 36 and 85% reductions of the current densities were caused by 1- and 10-μM pentamidine treatment (P<0.001 vs control), respectively. A similar level of reduction of the hERG polypeptides and a reduced intensity of the hERG protein on the surface membrane in treated cells were observed by Western blot analysis and laser-scanning confocal microscopy, respectively.
- 6Taken together, our data imply that chronic administration of pentamidine at clinically relevant exposure reduces the membrane expression of the hERG channel, which may most likely be the major mechanism of QT prolongation and torsade de pointes reported in man.
British Journal of Pharmacology (2005) 145, 15–23. doi:10.1038/sj.bjp.0706140