Activation of Calcium- and Voltage-gated Potassium Channels of Large Conductance by Leukotriene B4

Calcium/voltage-gated, large conductance potassium (BK) channels control numerous physiological processes, including myogenic tone. BK channel regulation by direct interaction between lipid and channel protein sites has received increasing attention. Leukotrienes (LTA4, LTB4, LTC4, LTD4, and LTE4) are inflammatory lipid mediators. We performed patch clamp studies in Xenopus oocytes that co-expressed BK channel-forming (cbv1) and accessory 1 subunits cloned from rat cerebral artery myocytes. Leukotrienes were applied at 0.1 nm-10 m to either leaflet of cell-free membranes at a wide range of [Ca2+](i) and voltages. Only LTB4 reversibly increased BK steady-state activity (EC50 = 1 nm; E-max reached at 10 nm), with physiological [Ca2+](i) and voltages favoring this activation. Homomeric cbv1 or cbv1-2 channels were LTB4-resistant. Computational modeling predicted that LTB4 docked onto the cholane steroid-sensing site in the BK 1 transmembrane domain 2 (TM2). Co-application of LTB4 and cholane steroid did not further increase LTB4-induced activation. LTB4 failed to activate 1 subunit-containing channels when 1 carried T169A, A176S, or K179I within the docking site. Co-application of LTB4 with LTA4, LTC4, LTD4, or LTE4 suppressed LTB4-induced activation. Inactive leukotrienes docked onto a portion of the site, probably preventing tight docking of LTB4. In summary, we document the ability of two endogenous lipids from different chemical families to share their site of action on a channel accessory subunit. Thus, cross-talk between leukotrienes and cholane steroids might converge on regulation of smooth muscle contractility via BK 1. Moreover, the identification of LTB4 as a highly potent ligand for BK channels is critical for the future development of 1-specific BK channel activators.