We report in this paper using measurement of intracellular free Ca2+ with fura-2, that flufenamic acid and several related blockers of the 25 pS Ca2+-activated nonselective cation channel cause release of Ca2+ from an intracellular store other than the endoplasmic reticulum, Possibly from mitochondria. A new compound, 4′-methyl-DPC, is found to be as effective in blocking non-selective cation channels as other flufenamate analogs but, like the parent compound, the non-selective cation channel blocker DPC, it does not cause release of Ca2+ from intracellular stores. DPC and 4′-methyl-DPC are thus the most suitable of the available blockers of non-selective cation channels for use in studies on the role of these channels in normal cell function.
