The efficiency of staining with SiR-probes varies with the cell type and/or the organism. One main reason for the observation of weak staining is the activity of efflux pumps in the sample. The addition of a broad spectrum efflux pump inhibitor such as verapamil has generally a positive effect on the signal intensity.

Guidelines for using Verapamil

If the fluorescence signal of your samples is weak, it is recommended to repeat the staining in the presence of Verapamil.

Dissolve the content of the tube in 100 μl DMSO to prepare a 10 mM (1000x) stock solution.

Add the Verapamil DMSO stock solution to the staining solution to a final concentration of 10 μM and incubate cells or sample as instructed for the SiR-probe (please refer to the datasheet of the SiR probe for a detailed staining protocol).

Important note: Verapamil is not a Spirochrome product and is added free of charge to every order. The above conditions are a recommended starting point as the effect of verapamil may vary with the cell type or organism used. Small scale experiments with varying concentrations of Verapamil and SiR-probe should be carried out to optimize the staining efficiency of weakly stained samples. As an efflux pump inhibitor and calcium channel inhibitor, Verapamil can have side effects on live samples.