Binding of compound 48/80 by isolated rat mast cells in connection with histamine release

The binding of compound 48/80 in connection with histamine release from isolated rat mast cells was investigated by a two-step incubation procedure. After incubation of mast cells with known concentrations of compound 48/80, the supernatants were collected and subsequently exposed to fresh mast cells. The response in the second incubation step provided a measure of the amount of compound 48/80 remaining in the supernatants. At noncytotoxic concentrations of the releasing agent, binding capacities for compound 48/80 of up to 4 micrograms/10(5) mast cells (4% w/v) were observed. The binding of compound 48/80 was of high affinity, giving mast cell concentrations of the compound exceeding that in the incubation medium by four orders of magnitude. The binding occurred rapidly with a substantial proportion bound within the first minute. These findings indicate that quantitation of exocytotic events by means of basic dyes may be compromised by competition for granular binding sites by basic releasing agents.