Glycyrrhetinic acid derivatives block hyperpolarization concomitant with intercellular coupling along microvascular endothelial tubes

Cell‐to‐cell conduction of hyperpolarization through gap junctions along endothelial cells promotes smooth muscle cell hyperpolarization and vasodilation. Using intact endothelial tubes (width, ~60 μm; length, 700–2000 μm) isolated from mouse abdominal feed arteries and devoid of smooth muscle cells, we tested the hypothesis that purported gap junction blockers carbenoxolone (CBX, 100 μM) or β‐glycyrrhetinic acid (βGA, 30 μM) would inhibit conducted hyperpolarization. Dual simultaneous intracellular recording confirmed stability of membrane potential (V m ) at 2 sites separated by 500 μm (V m1 = −24±2, V m2 = −23 ± 1 mV; n=14). Injecting negative current (−0.5 to −5 nA) at Site 1 produced hyperpolarization at Site 2 (−3 to −30 mV). Calculated transfer resistance (TR = ΔV m at Site 2/current injected at Site 1) was 6.2 ± 0.6 MΩ (n=9). Either CBX or βGA eliminated ΔV m at Site 2 (TR=0; n=6, P<0.05); αGA (100 μM) had no effect (n=3). Remarkably, CBX or βGA also inhibited hyperpolarization to either 3 μM acetylcholine [from −39 ± 2 (control) to −3 ± 1 mV (treatment; n=18, P<0.05)] or to 1 μM NS309 [from −33 ± 4 to −1 ± 1 mV (n = 5, P<0.05)]. These findings illustrate that glycyrrhetinic acid derivatives purported to block gap junctions concomitantly block endothelial cell hyperpolarization. (Support: HL056786, HL041026, HL086483)