WIN 17317-3, a new high-affinity probe for voltage-gated sodium channels

The iminodihydroquinoline WIN 17317-3 was previously shown to inhibit selec tively the voltage-gated potassium channels, K(v)1.3 and K(v)1.4 [Hill, R. J., et al. (1995) Mel. Pharmacol. 48, 98-104; Nguyen, A., et al. (1996) Mel . Pharmacol. 50, 1672-1679]. Since these channels are found in brain, radio labeled WIN 17317-3 was synthesized to probe neuronal K(v)1 channels. In ra t brain synaptic membranes, [H-3]WIN 17317-3 binds reversibly and saturably to a single class of high-affinity sites (K-d 2.2 +/- 0.3 nM; B-max 5.4 +/ - 0.2 pmol/mg of protein). However, the interaction of [H-3]WIN 17317-3 wit h brain membranes is not sensitive to any of several well-characterized pot assium channel ligands. Rather, binding is modulated by numerous structural ly unrelated sodium channel effecters (e.g., channel toxins, local anesthet ics, antiarrhythmics, and cardiotonics). The potency and rank order of effe ctiveness of these agents in affecting [H-3]WIN 17317-3 binding is consiste nt with their known abilities to modify sodium channel activity. Autoradiog rams of rat brain sections indicate that the distribution of [H-3]WIN 17317 -3 binding sites is in excellent agreement with that of sodium channels. Fu rthermore, WIN 17317-3 inhibits sodium currents in CHO cells stably transfe cted with the rat brain IIA sodium channel with high affinity (K-i 9 nM), a s well as agonist-stimulated Na-22 uptake in this cell line. WIN 17317-3 in teracts similarly with skeletal muscle sodium channels but is a weaker inhi bitor of the cardiac sodium channel. Together, these results demonstrate th at WIN 17317-3 is a new, high-affinity, subtype-selective ligand for sodium channels and is a potent blocker of brain IIA sodium channels.