TY - JOUR T1 - Bromoenol Lactone Inhibits Voltage-Gated Ca<sup>2+</sup> and Transient Receptor Potential Canonical Channels JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 329 LP - 340 DO - 10.1124/jpet.111.183673 VL - 339 IS - 2 AU - Saikat Chakraborty AU - Zachary C. Berwick AU - Paula J. Bartlett AU - Sanjay Kumar AU - Andrew P. Thomas AU - Michael Sturek AU - Johnathan D. Tune AU - Alexander G. Obukhov Y1 - 2011/11/01 UR - http://jpet.aspetjournals.org/content/339/2/329.abstract N2 - Circulating hormones stimulate the phospholipase Cβ (PLC)/Ca2+ influx pathway to regulate numerous cell functions, including vascular tone. It was proposed previously that Ca2+-independent phospholipase A2 (iPLA2)-dependent store-operated Ca2+ influx channels mediate hormone-induced contractions in isolated arteries, because bromoenol lactone (BEL), a potent irreversible inhibitor of iPLA2, inhibited such contractions. However, the effects of BEL on other channels implicated in mediating hormone-induced vessel contractions, specifically voltage-gated Ca2+ (CaV1.2) and transient receptor potential canonical (TRPC) channels, have not been defined clearly. Using isometric tension measurements, we found that thapsigargin-induced contractions were ∼34% of those evoked by phenylephrine or KCl. BEL completely inhibited not only thapsigargin- but also phenylephrine- and KCl-induced ring contractions, suggesting that CaV1.2 and receptor-operated TRPC channels also may be sensitive to BEL. Therefore, we investigated the effects of BEL on heterologously expressed CaV1.2 and TRPC channels in human embryonic kidney cells, a model system that allows probing of individual protein function without interference from other signaling elements of native cells. We found that low micromolar concentrations of BEL inhibited CaV1.2, TRPC5, TRPC6, and heteromeric TRPC1–TRPC5 channels in an iPLA2-independent manner. BEL also attenuated PLC activity, suggesting that the compound may inhibit TRPC channel activity in part by interfering with an initial PLC-dependent step required for TRPC channel activation. Conversely, BEL did not affect endogenous voltage-gated K+ channels in human embryonic kidney cells. Our findings support the hypothesis that iPLA2-dependent store-operated Ca2+ influx channels and iPLA2-independent hormone-operated TRPC channels can serve as smooth muscle depolarization triggers to activate CaV1.2 channels and to regulate vascular tone. ER -