CHARACTERISTICS OF SPECIFIC I-125 OMEGA-CONOTOXIN GVIA BINDING IN RAT WHOLE-BRAIN

Characteristics of specific I-125-omega-conotoxin (omega-CgTX) binding were systematically investigated in crude membranes from rat whole brain. Kd and Bmax Values for the binding were 49.7 pM and 181.5 fmol/mg of protein, respectively. The effects of various types of Ca channel antagonists on the binding were investigated. Dynorphin A (1-13), in particular, specifically inhibited I-125-omega-CgTX binding, but not that of [H-3](+)PN200-110. Spider venom from Plectreurys tristes did not specifically inhibit specific binding of I-125-omega-CgTX, because the venom also inhibited the binding of [H-3](+)PN200-110 to a similar degree. The amount of specific binding of I-125-omega-CgTX was less in the cerebellum than that in any other area of whole brain. The cross-linker disuccinimidyl suberate did not label with I-125-omega-CgTX and its binding sites in rat whole brain, although it did in chick whole brain, which was used as a positive control. These findings suggested that dynorphine A (1-13) was a selective blocker of omega-CgTX-sensitive Ca channels in crude membranes from rat whole brain and that omega-CgTX-sensitive Ca channels were mainly present a rat brain except cerebellum.