correolide and agitoxin-2

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

1. In this study we investigated the expression and function of the K(V)alpha1 subfamily of voltage-gated K(+) channels in terminal arterioles from rabbit cerebral circulation. 2. K(+) current was measured from smooth muscle cells within intact freshly isolated arteriolar fragments. Current activated on depolarisation positive of about -45 mV and a large fraction of this current was blocked by 3,4-diaminopyridine (3,4-DAP) or 4-aminopyridine (4-AP), inhibitors of K(V) channels. Expression of cRNA encoding K(V)1.6 in Xenopus oocytes also generated a 4-AP-sensitive K(+) current with a threshold for activation near -45 mV. 3. Immunofluorescence labelling revealed K(V)1.2 to be specifically localised to endothelial cells, and K(V)1.5 and K(V)1.6 to plasma membranes of smooth muscle cells. 4. K(V) channel current in arteriolar fragments was blocked by correolide (which is specific for the K(V)alpha1 family of K(V) channels) but was resistant to recombinant agitoxin-2 (rAgTX2; which inhibits K(V)1.6 but not K(V)1.5). Heterologously expressed K(V)2.1 was resistant to correolide, and K(V)1.6 was blocked by rAgTX2. 5. Arterioles that were mildly preconstricted and depolarised by 0.1-0.3 nM endothelin-1 constricted further in response to 3,4-DAP, 4-AP or correolide, but not to rAgTX2. 6. We suggest that K(V)alpha1 channels are expressed in smooth muscle cells of terminal arterioles, underlie a major part of the voltage-dependent K(+) current, and have a physiological function to oppose vasoconstriction. K(V)alpha1 complexes without K(V)1.5 appear to be uncommon.

Topics: 4-Aminopyridine; Amifampridine; Animals; Arterioles; Cell Membrane; Cerebrovascular Circulation; Delayed Rectifier Potassium Channels; Electric Conductivity; Endothelium, Vascular; Kv1.2 Potassium Channel; Kv1.5 Potassium Channel; Male; Muscle, Smooth, Vascular; Oocytes; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Voltage-Gated; Rabbits; Scorpion Venoms; Tissue Distribution; Triterpenes; Xenopus laevis

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