Permeabilization of transformed mouse fibroblasts by 3′‐O‐(4‐benzoyl)benzoyl adenosine 5′‐triphosphate and the desensitization of the process

Abstract

A photoreactive analogue of ATP, 3′‐O‐(4‐benzoyl)benzoyl adenosine 5′‐triphosphate (BzATP) altered the plasma membrane permeability of transformed 3T6 mouse fibroblasts to normally impermeant molecules as previously reported for ATP, but at lower concentrations. BzATP‐induced permeabilization was modulated by pH, temperature, and the ionic composition of the medium similar to the permeabilizing effects of ATP. Conditions known to enhance ATP‐induced permeabilization, such as treatment with the mitochondrial uncoupler carbonyl cyanide‐m‐chlorophenylhydrazone (CCCP) or the Ca²⁺‐calmodulin antagonist trifluoperazine also enhanced BzATP‐induced permeabilization. Conditions inhibitory to ATP‐induced permeabilization, including chloride replacement or treatment with furosemide or dithiothreitol (DTT), inhibited permeabilization induced by BzATP. The ionic strength of the medium modulated the responsiveness of the cells to ATP and BzATP; a decrease in the ionic strength below isotonicity increased the sensitivity of the cells to the nucleotides, whereas an increase in ionic strength above isotonicity inhibited permeabilization. Prolonged exposure to ATP under non‐permeabilizing conditions caused the cells to become insensitive to ATP and BzATP. The densensitization phenomenon provides support for the theory that the permeabilization process is mediated by a receptor for ATP.