Non-specific effects of calcium entry antagonists in mast cells.

Calcium entry in non-excitable cells occurs through calcium-selective currents activated secondarily to store depletion and/or through non-selective cation channels (e.g., receptor- or second-messenger-activated channels). The driving force for calcium influx can be modified by chloride or potassium channels, which set the membrane potential of cells. Together, these conductances determine the extent of calcium entry. Mast cells are an excellent model system for studying calcium influx, because calcium-release-activated calcium currents (ICRAC), second-messenger-activated non-selective currents and chloride currents are present in these cells. Whole-cell patch-clamp recordings were used to test the effects of the commonly used calcium entry blockers econazole and SK&F 96365, as well as the antiallergic and anti-inflammatory drugs tenidap, ketotifen and cromolyn on these channels. All tested drugs blocked the three different channel types with a similar order of magnitude (IC50 values ranging from micromolar to millimolar). Hence, these drugs cannot be used to discriminate between different calcium entry mechanisms.