The action on pigeon erythrocytes of the Ca2+ ionophore, A23187, can be nearly completely stopped within 30 s by treatment with a phosphatidylcholine dispersion at 39°C. A time-limited 45Ca2+ uptake pulse can be produced by treating cells sequentially with A23187 and lipid, and the time-course of expulsion of this 45Ca2+ uptake pulse can be easily determined.
