Identification and biochemical characterization of a novel nortriterpene inhibitor of the human lymphocyte voltage-gated potassium channel, Kv1.3

A novel nortriterpene, termed correolide, purified from the tree Spachea co rreae, inhibits Kv1.3, a Shaker-type delayed rectifier potassium channel pr esent in human T lymphocytes. Correolide inhibits Rb-86(+) efflux through K v1.3 channels expressed in CHO cells (IC50 86 nM; Hill coefficient 1) and d isplays a defined structure-activity relationship. Potency in this assay in creases with preincubation time and with time after channel opening. Correo lide displays marked selectivity against numerous receptors and voltage- an d ligand-gated ion channels. Although correolide is most potent as a Kv1.3 inhibitor, it blocks all other members of the Kv1 family with 4-14-fold low er potency. C20-29-[H-3]dihydrocorreolide (diTC) was prepared and shown to bind in a specific, saturable, and reversible fashion (K-d = 11 nM) to a si ngle class of sites in membranes prepared from CHO/Kv1.3 cells. The molecul ar pharmacology and stoichiometry of this binding reaction suggest that one diTC site is present per Kv1.3 channel tetramer. This site is allosterical ly coupled to peptide and potassium binding sites in the pore of the channe l. DiTC binding to human brain synaptic membranes identifies channels compo sed of other Kv1 family members. Correolide depolarizes human T cells to th e same extent as peptidyl inhibitors of Kv1.3, suggesting that it is a cand idate for development as an immunosuppressant. Correolide is the first pote nt, small molecule inhibitor of Kv1 series channels to be identified from a natural product source and will be useful as a probe for studying potassiu m channel structure and the physiological role of such channels in target t issues of interest.