correolide and margatoxin

The aim of the study was to determine the potential for K(V)1 potassium channel blockers as inhibitors of human neoinitimal hyperplasia.. Blood vessels were obtained from patients or mice and studied in culture. Reverse transcriptase-polymerase chain reaction and immunocytochemistry were used to detect gene expression. Whole-cell patch-clamp, intracellular calcium measurement, cell migration assays, and organ culture were used to assess channel function. K(V)1.3 was unique among the K(V)1 channels in showing preserved and up-regulated expression when the vascular smooth muscle cells switched to the proliferating phenotype. There was strong expression in neointimal formations. Voltage-dependent potassium current in proliferating cells was sensitive to three different blockers of K(V)1.3 channels. Calcium entry was also inhibited. All three blockers reduced vascular smooth muscle cell migration and the effects were non-additive. One of the blockers (margatoxin) was highly potent, suppressing cell migration with an IC(50) of 85 pM. Two of the blockers were tested in organ-cultured human vein samples and both inhibited neointimal hyperplasia.. K(V)1.3 potassium channels are functional in proliferating mouse and human vascular smooth muscle cells and have positive effects on cell migration. Blockers of the channels may be useful as inhibitors of neointimal hyperplasia and other unwanted vascular remodelling events.

Topics: Animals; Aorta, Thoracic; Calcium; Cell Movement; Cell Proliferation; Cells, Cultured; Dose-Response Relationship, Drug; Ficusin; Humans; Hyperplasia; Immunohistochemistry; Kv1.3 Potassium Channel; Male; Membrane Potentials; Mice; Mice, Inbred C57BL; Muscle, Smooth, Vascular; Myocytes, Smooth Muscle; Organ Culture Techniques; Patch-Clamp Techniques; Potassium Channel Blockers; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Saphenous Vein; Scorpion Venoms; Time Factors; Triterpenes; Tunica Intima

Hypoxic fetoplacental vasoconstriction (HFPV), involving voltage-gated potassium (K(V)) channels, has been suggested in human placenta; the identity of these channels remains unclear. Using wire myography, chorionic plate blood vessels were exposed to isoform-specific K(V) channel blockers. Dose-response curves (thromboxane mimetic U46619; 0.1-2000 nM) pre- and post-addition of K(V) channel modulator were analysed. Arterial U46619-induced contraction increased with margatoxin and stromatoxin-1, whilst only correolide increased U46619-induced contraction in veins (P < 0.05 two-way ANOVA). Basal tone was unaffected in arteries or veins. These data implicate K(V)1.2 and/or K(V)2.1 and K(V)1.5 in the control of agonist-induced contraction of human placental arteries and veins respectively.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Analysis of Variance; Arteries; Dose-Response Relationship, Drug; Female; Humans; Placenta; Pregnancy; Scorpion Venoms; Shaker Superfamily of Potassium Channels; Triterpenes; Vasoconstriction; Veins

A novel nortriterpene, termed correolide, purified from the tree Spachea correae, inhibits Kv1.3, a Shaker-type delayed rectifier potassium channel present in human T lymphocytes. Correolide inhibits 86Rb+ efflux through Kv1.3 channels expressed in CHO cells (IC50 86 nM; Hill coefficient 1) and displays a defined structure-activity relationship. Potency in this assay increases with preincubation time and with time after channel opening. Correolide displays marked selectivity against numerous receptors and voltage- and 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 lower potency. C20-29-[3H]dihydrocorreolide (diTC) was prepared and shown to bind in a specific, saturable, and reversible fashion (Kd = 11 nM) to a single class of sites in membranes prepared from CHO/Kv1.3 cells. The molecular pharmacology and stoichiometry of this binding reaction suggest that one diTC site is present per Kv1.3 channel tetramer. This site is allosterically coupled to peptide and potassium binding sites in the pore of the channel. DiTC binding to human brain synaptic membranes identifies channels composed of other Kv1 family members. Correolide depolarizes human T cells to the same extent as peptidyl inhibitors of Kv1.3, suggesting that it is a candidate for development as an immunosuppressant. Correolide is the first potent, small molecule inhibitor of Kv1 series channels to be identified from a natural product source and will be useful as a probe for studying potassium channel structure and the physiological role of such channels in target tissues of interest.

Topics: Animals; Binding Sites; Cell Line; Charybdotoxin; CHO Cells; Cricetinae; Humans; Immunosuppressive Agents; Ion Channel Gating; Kv1.3 Potassium Channel; Membrane Potentials; Neurotoxins; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Voltage-Gated; Rubidium Radioisotopes; Scorpion Venoms; Synaptic Membranes; T-Lymphocytes; Triterpenes