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20-HETE inotropic effects involve the activation of a nonselective cationic current in airway smooth muscle

Faculty of Medicine, Department of Physiology and Biophysics, University of Sherbrooke, Sherbrooke, Quebec, Canada J1H 5N4

Submitted 8 November 2002 ; accepted in final form 5 May 2003

20-Hydroxyeicosatetraenoic acid (20-HETE) controls several mechanisms such as vasoactivity, mitogenicity, and ion transport in various tissues. Our goal was to quantify the effects of 20-HETE on the electrophysiological properties of airway smooth muscle (ASM). Isometric tension measurements, performed on guinea pig ASM, showed that 20-HETE induced a dose-dependent inotropic effect with an EC₅₀ value of 1.5 µM. This inotropic response was insensitive to GF-109203X, a PKC inhibitor. The sustained contraction, requiring Ca²⁺ entry, was partially blocked by either 100 µM Gd³⁺ or 1 µM nifedipine, revealing the involvement of noncapacitative Ca²⁺ entry and L-type Ca²⁺ channels, respectively. Microelectrode measurements showed that 3 µM 20-HETE depolarized the membrane potential in guinea pig ASM by 13 ± 2mV(n = 7), as did 30 µM 1-oleoyl-2-acetyl-sn-glycerol. Depolarizing effects were also observed in the absence of epithelium. Patch-clamp recordings demonstrated that 1 µM 20-HETE activated a nonselective cationic inward current that may be supported by the activation of transient receptor potential channels. The presence of canonical transient receptor potential mRNA was confirmed by RT-PCR in guinea pig ASM cells.

20-hydroxyeicosatetraenoic acid; calcium; isometric tension; membrane potential; transient receptor potential; nonselective cationic current

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