Linoleic acid both enhances activation and blocks Kv1.5 and Kv2.1 channels by two separate mechanisms

Linoleic acid (LA) had twoeffects on human Kv1.5 and Kv2.1 channels expressed in Chinese hamsterovary cells: an increase in the speed of current activation process(EC₅₀ = 2.4 and 2.7 µM for Kv1.5 and Kv2.1,respectively) and current inhibition (IC₅₀ = 6.6 and7.4 for Kv1.5 and Kv2.1, respectively). LA affected the activationkinetics via two processes: a leftward shift in the instantaneousactivation curves and an increase in the rate of current rise. Currentinhibition by LA was time dependent but voltage independent. Hillslopes for plots of current inhibition (3.5 and 3.9 for Kv1.5 andKv2.1, respectively) vs. dose of LA suggested that cooperativity wasinvolved in the mechanism of current inhibition. A similar analysis ofthe effects of LA on current activation did not reveal cooperativeinteractions. The effects of LA were mediated from the external side ofthe channels, since addition of 10 µM LA to the patch pipettesolution was without effect. Additionally, the methyl ester of LA waseffective at enhancing peak current and promoting channel activationfor Kv1.5 and Kv2.1 without inducing significant current inhibition.