Binding of a spin label analogue of compound 48/80 to rat peritoneal mast cells: correlation of binding properties with surface topography.

A spin label analogue of compound 48/80 has been synthesized and its binding to purified rat peritoneal mast cells has been studied by electron spin resonance spectroscopy. The spin label analogue (SL-48/80) had almost identical biological activity to unlabeled compound 48/80. SL-48/80 was used to estimate the number of binding sites per cell on normal mast cells (7.25 X 10(10)), on mast cells deactivated by sodium azide and 2-deoxyglucose or by heating to 46 degrees for 30 min (1 X 10(10)) and cells from animals actively-sensitized to ovalbumin (5.2 X 10(10)). SL-48/80 was also shown to bind to isolated mast cell granules. Differences in the binding properties of mast cells after the different treatments are related to their surface topography as seen by scanning electron microscopy, and the contribution of the granules to the number of binding sites is discussed.