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(Circulation Research. 1996;79:20-31.)
© 1996 American Heart Association, Inc.

Articles

Modulatory Effects of Arachidonic Acid on the Delayed Rectifier K⁺ Current in Rat Pulmonary Arterial Myocytes

Structural Aspects and Involvement of Protein Kinase C

Sergey V. Smirnov, Philip I. Aaronson

the Department of Pharmacology, United Medical and Dental Schools of Guy's and St Thomas's Hospitals, London, UK.

Correspondence to Dr S.V. Smirnov, Department of Pharmacology, United Medical and Dental Schools of Guy's and St Thomas's Hospitals, St Thomas's Campus, Lambeth Palace Rd, London SE1 7EH, UK. E-mail s.smirnov@umds.ac.uk.

The effect of arachidonic acid (AA) on the delayed rectifier K⁺ current (I_K) was evaluated in rat pulmonary myocytes by using the whole-cell patch-clamp technique. Externally applied AA (50 µmol/L) caused a membrane depolarization, averaging 16 mV in six cells. AA (1 to 50 µmol/L) caused a dual effect on I_K. First, AA accelerated the rate of I_K activation, increasing current amplitude at the beginning of voltage step. Second, AA caused a marked acceleration of current decay, thereby reducing I_K amplitude measured toward the end of the depolarizing steps. These effects were not prevented by indomethacin or nordihydroguaiaretic acid, blockers of cyclooxygenase and lipoxygenase, respectively. AA did not affect the voltage dependence of current activation or inactivation. The magnitude of the inhibitory effect on I_K was correlated with the number of double bonds but was independent of tail length in fatty acids containing between 14 and 22 carbons. Linoleic acid (18:2, cis-9,12) inhibited I_K much more than did its trans-stereoisomer, linolelaidic acid. Arachidonyl alcohol, which is uncharged, and arachidonyl coenzyme A, which does not `flip' across the cell membrane, were less effective than AA in inhibiting I_K; this effect of fatty acids may therefore require passage across the cell membrane. The enhancement of early I_K was mimicked by the protein kinase C (PKC) stimulator 1-oleoyl-2-acetyl-sn-glycerol (10 µmol/L), was suppressed by ATP removal from the pipette solution, and was blocked by PKC inhibitors chelerythrine (10 µmol/L) and staurosporine (100 nmol/L). This effect may therefore require PKC-dependent phosphorylation.

Key Words: vascular smooth muscle • pulmonary artery • K⁺ channel • arachidonic acid • protein kinase C

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