A Role for Heterocellular Coupling and EETs in Dilation of Rat Cremaster Arteries

Abstract

Objective: The authors probed endothelium-dependent dilation and endothelial cell Ca^{2 +} handling in myogenically active resistance arteries.

Methods: First-order arteries were removed from rat cremaster muscles, cannulated, and pressurized (75 mmHg). Vessel diameter and endothelial cell Ca^{2 +} were monitored using confocal microscopy, and arterial ultrastructure was determined using electron microscopy.

Results: Acetylcholine (ACh) stimulated elevations and oscillations in endothelial cell Ca^{2 +}, and concentration-dependently dilated arteries with myogenic tone. NO-independent dilation was blocked by 35 mM K⁺. Combined IK_Ca (1 μ M TRAM-34) and SK_Ca (100 nM apamin) blockade partially inhibited NO-independent relaxations, with residual relaxations sensitive to BK_Ca or cytochrome P-450 inhibition (100 nM iberiotoxin, and 20 μ M 17-ODYA or 10 μ M MS-PPOH). 11,12-EET stimulated iberiotoxin-sensitive dilation, but did not affect endothelial cell Ca^{2 +}. 15 mM K⁺ evoked dilation sensitive to inhibition of K_IR (30 μ M Ba^{2 +}) and Na⁺/K⁺-ATPase (10 μ M ouabain), whereas these blockers did not affect ACh-mediated dilations. Homo- and heterocellular gap junctions were identified in radial sections through arteries.

Conclusion:These data suggest that rises in endothelial cell Ca^{2 +} stimulate SK_Ca and IK_Ca channels, leading to hyperpolarization and dilation, likely due to electrical coupling. In addition, a component was unmasked following SK_Ca and IK_Ca blockade, attributable to activation of BK_Ca channels by cytochrome P-450 metabolites.

KEY WORDS:

• calcium
• Ca^{2 +}-activated K⁺ channel
• EDHF
• endothelial cell

This work was supported by British Heart Foundation, Wellcome Trust (UK), NIH (HL-51055), and NIH (GM-31278).