[¹²⁵I]Tyr-bradykinin binding in primary rat brain cultures

Kinins bind to specific, high affinity recognition sites in rat brain cell culture. Studies in these cultures minimize non-specific binding and degradation of the ligand. Binding of [¹²⁵I]Tyr-bradykinin to intact cultured brain cells from neonatal rats was time- and pH-dependent. Scatchard analysis of saturation experiments yielded two affinity components with dissociation constant and maximum binding site concentration averaging 1 nM and 100 fmol/mg protein, and 16 M and 1000 fmol/mg protein, respectively. The binding sites were specific for kinins and kinin analogues, and the order of potency in competing for [¹²⁵I]Tyr-bradykinin binding was Lys-bradykinin > bradykinin > Tyr-bradykinin > Tyr-⁸-bradykinin ⋙ Des-Arg⁹-bradykinin. Monovalent and divalent cations inhibited kinin binding. Comparison of competition curves performed in glial-enriched vs neuron-enriched cultures suggested that the kinin binding sites resided primarily on neurons. These data enhance the existing evidence suggesting kinins as neurotransmitters or neuromodulators.