Endothelin-1 inhibits inward rectifier K+ channels in rabbit coronary arterial smooth muscle cells through protein kinase C

Abstract

We studied inward rectifier K+ (Kir) channels in smooth muscle cells isolated from rabbit coronary arteries. In cells from small-(<100 μm, SCASMC) and medium-diameter (100 ∼ 200 μm, MCASMC) coronary arteries, Kir currents were clearly identified (11.2 ± 0.6 and 4.2 ± 0.6 pA pF-1 at -140 mV in SCASMC and MCASMC, respectively) that were inhibited by Ba2+ (50 μM). By contrast, a very low Kir current density (1.6 ± 0.4 pA pF-1) was detected in cells from large-diameter coronary arteries (>200 μm, LCASMC). The presence of Kir2.1 protein was confirmed in SCASMC in a Western blot assay. Endothelin-1 (ET-1) inhibited Kir currents in a dose-dependent manner. The inhibition of Kir currents by ET-1 was abolished by pretreatment with the protein kinase C (PKC) inhibitor staurosporine (100 nM) or GF 109203X (1 μM). The PKC activators phorbol 12,13-dibutyrate (PDBu) and 1-oleoyl-2-acetyl-sn-glycerol (OAG) reduced Kir currents. The ETA-receptor inhibitor BQ-123 prevented the ET-1-induced inhibition of Kir currents. The amplitudes of the ATP-dependent K+ (KATP), Ca2+-activated K+ (BKCa), and voltage-dependent K+ (KV) currents, and effects of ET-1 on these channels did not differ between SCASMC and LCASMC. From these results, we conclude that Kir channels are expressed at a higher density in SCASMC than in larger arteries and that the Kir channel activity is negatively regulated by the stimulation of ETA-receptors via the PKC pathway. Copyright © 2005 by Lippincott Williams & Wilkins.