Extracellular ATP (0.6 mM) induces a marked decrease in the membrane potential, followed by an increase in cell membrane permeability in transformed mouse fibroblasts. The effects of the ATP analogs, p[CH2]ppA and p[NH]ppA (0.6 mM), on the membrane potential and permeability are much less pronounced. ATP at 0.05 mM has no effect by itself, but markedly increases the analog-induced membrane potential dissipation and permeability. The data suggest that ATP-induced membrane permeation is composed of two processes: One is common to ATP and its analogs and appears to be a receptormediated process. The second is unique for ATP, effective even at low concentration (0.05 mM), and might be mediated by cell surface enzymes, for which ATP, but not its analogs, serves as a substrate.
