Arachidonic Acid Inhibits the Activity of the Cloned Renal K+ Channel, ROMK1. Macica, Carolyn M., Yinhai Yang, Steven C. Hebert, and Wen Hui Wang. Department of Pharmacology, New York Medical College, Valhalla, New York 10595 and Department of Medicine, Renal Division, Brigham & Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115
APStracts 3:0084F, 1996.
Arachidonic Acid (AA) has been shown to inhibit the activity of the low- conductance ATP-sensitive K + channel in the apical membrane of the cortical collecting duct (28). ROMK1, a K + channel derived from the rat renal outer medulla, shares many biophysical properties of the native low conductance K + channel, which is localized to the apical membranes of the cortical collecting duct and thick ascending limb. This study was designed to determine whether the ROMK + channel maintains the property of AA sensitivity of the native low- conductance K + channel. Experiments were conducted in xenopus oocytes injected with cRNA encoding the ROMK1 channel, using patch clamp techniques. We have confirmed previous reports that the cloned ROMK1 has similar channel kinetics, high open probability and inward slope conductance as the native low-conductance K + channel, respectively. Addition of 5 [mu]M AA to an inside-out patch resulted in reversible inhibition of channel activity at a concentration which was similar to the Ki for AA on the native K + channel (28). The effect of AA on channel activity was preserved in the presence of 10 [mu]M indomethacin, a cyclooxygenase inhibitor, 4 [mu]M cinnamyl-3,4- dihydroxy-cyanocinnamate, a lipoxygenase inhibitor, and 4[mu]M 17-octadecynoic acid, and inhibitor of cytochrome P450 monoxygenases thus indicating that the effect of AA was not mediated by metabolites of AA. The effect did not appear to be the result of changes in membrane fluidity since 5 [mu]M ETYA, an AA analog which is a potent modulator of membrane fluidity, had no effect. Furthermore, the addition of AA to the outside of the patch also had no effect on channel activity. These results indicate that, like the native low- conductance channel, AA is able to directly inhibit ROMK1 channel activity. 

Received 6 February 1996; accepted in final form 30 April 1996.
APS Manuscript Number F40-6.
Article publication pending Am. J. Physiol. (Renal, Fluid, Elect.Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 May 96