Specific binding properties of ¹²⁵I-apamin in various structures of the rat central nervous system

The properties of ¹²⁵I-apamin binding with rat central nervous system slices were analysed in vitro using computerized densitometric autoradiography. Scatchard analysis performed for the data of binding experiments in rat brain and spinal cord demonstrates that apamin binds to a single class of non-interacting binding sites in all investigated structures. The dissociation constant values (K(D)) were similar in all investigated structures (31-38 pM). The maximal binding capacity (B(max)) was observed in the structures of limbic olfactory system (30 fmol/mg protein), the lowest in brain white matter (0.5 fmol/mg protein). It is concluded that the observed pattern of ¹²⁵I-apamin binding might represent the topography of a class of Ca²⁺ dependent K⁺ channels in the rat central nervous system.