Recognition of the ‘calcium paradox’ and the effects of verapamil and gallopamil in human adenoidal mast cells

Human mast cells from adenoids show when resuspended in medium containing 10−3M CaCl2 after their temporary exposure to Ca2+-free saline for about 20 min an irreversible reduction of responsiveness to a variety of stimuli: The histamine release induced by concanavalin A or ionophore A 23187 is only 30–50% of the one obtained in cells which were kept in 10−3M Ca2+ throughout the experiment. This phenomenon called ‘calcium paradox’ can be almost entirely avoided if the cells are temporarily exposed to 10−4M Ca2+ instead of Ca2+-free saline. Number yields, average histamine contents of mast cells and the rate of the spontaneous histamine release are not affected by the transitory lack of Ca2+, nor is the histamine release enhancing effect of adenosine.