A role for heterocellular coupling and EETs in dilation of rat cremaster arteries

Objective: The authors probed endothelium-dependent dilation and endothelial cell Ca²⁺ 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 Ca²⁺ were monitored using confocal microscopy, and arterial ultrastructure was determined using electron microscopy. Results: Acetylcholine (ACh) stimulated elevations and oscillations in endothelial cell Ca²⁺, and concentration-dependently dilated arteries with myogenic tone. NO-independent dilation was blocked by 35 mM K⁺. Combined IK _Ca (1 μM 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 μM 17-ODYA or 10 μM MS-PPOH). 11,12-EET stimulated iberiotoxin-sensitive dilation, but did not affect endothelial cell Ca²⁺. 15 mM K⁺ evoked dilation sensitive to inhibition of K_IR (30 μM Ba²⁺) and Na⁺/K⁺ -ATPase (10 μM 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 Ca²⁺ 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.